Materiały źródłowe

• #1 How to Prevent Muscle Strains • Stronger by Science

  https://www.strongerbyscience.com/how-to-prevent-muscle-strains/

  A muscle strain occurs when the strain energy the muscle is forced to absorb exceeds the strength of the tissue. […] A muscle strain is an indirect, structural injury. They’re often referred to as pulled or tweaked muscles. […] Strain energy is the key determinant of injury. […] Although the cause of acute muscle strains is often complex and multifactorial, most strains in strength training do share several common features. […] The precise location of a tear is a function of the distribution of stress throughout the tissue, but it’s most likely to happen near the junction between the muscle and tendon, because the transitional tissue is a bit weaker than either the muscle or tendon. […] The muscles most susceptible to strain injury include the hamstrings, quadriceps, hip adductors, hip flexors, abdominals, calves, and biceps.

• #1 Musculoskeletal sprains and strains – Symptoms, diagnosis and treatment | BMJ Best Practice US

  https://bestpractice.bmj.com/topics/en-us/578

  Muscle injuries occur from either direct or indirect trauma. […] Predisposing factors include type of muscle architecture (i.e., pennate muscle, type II fast twitch muscle fibers, muscle-tendon units that span 2 joints), previous injury, and inadequate warm-up before exercise. […] Eccentric contraction (i.e., muscle contraction associated with forcible lengthening of the contracting muscle, such as when lowering a weight or pitching a ball) causes more frequent injury. […] In strains, an excessive tensile force subjected onto the muscle leads to the overstraining of the myofibers and consequently to a rupture near the musculotendinous junction. […] Muscle strains typically concern the superficial muscles working across 2 joints, such as the rectus femoris, semitendinosus, and gastrocnemius muscles. […] Muscle strain usually occurs in eccentric exercise. […] In eccentric exercise the contracting muscle is forcibly lengthened; in concentric exercise it shortens. […] While concentric contractions initiate movements, eccentric contractions slow or stop them (e.g., when lowering a weight).

• #1 Explorations in Hamstring Injury Concepts – Part II: Mechanism of Injury

  https://www.linkedin.com/pulse/explorations-hamstring-injury-concepts-part-ii-ryan

  Two specific injury mechanisms are most often associated with (but are not limited to) hamstring strains. The first and more common type results from high-speed running and often involves an injury to the LHBF (Erickson and Sherry, 2017). […] The second type which is worth noting, but will not be discussed in as great of detail is coined the excessive stretching or overstretching type. This injury typically involves the proximal free tendon of the semimembranosus (Erickson and Sherry, 2017). […] As it relates to the first type of injury, I’ve seen two incredibly well-done webinars that discuss in great detail how this MOI may occur. […] The first given by Bryan Heiderscheit discusses the belief that these injuries occur when the hamstrings are subjected to periods of peak eccentric force, as most often seen during the terminal swing phase of running.

• #1 The mechanism of hamstring injuries – a systematic review | BMC Musculoskeletal Disorders | Full Text

  https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/s12891-020-03658-8

  Injuries to the hamstring muscles are among the most common in sports and account for significant time loss. Despite being so common, the injury mechanism of hamstring injuries remains to be determined. […] All studies that reported the stretch-type injury mechanism concluded that injury occurs due to extensive hip flexion with a hyperextended knee. The vast majority of studies on injuries during running proposed that these injuries occur during the late swing phase of the running gait cycle. […] A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle. […] All the studies of stretch-type injuries concluded that injuries occur due to extensive hip flexion with simultaneous knee extension.

• #1 Cellular mechanism of eccentric-induced muscle injury and its relationship with sarcomere heterogeneity

  https://www.e-jer.org/journal/view.php?number=2013600137

  Activity-induced muscle injury and dysfunction have been identified as key components of musculoskeletal injuries. […] General features of eccentric-induced muscle injury are well documented and include disruption of intracellular muscle structure, prolonged muscle weakness and dysfunction, a delayed-onset muscle soreness, and inflammation. […] Possible mechanisms responsible for eccentric-induced muscle injury are activation impairment and structural disruption of the sarcomere. […] The first possible mechanism is a failure of Ca2+ release and up-take. […] Warren and associates proposed that impaired EC coupling plays a major role in eccentric-induced muscle injury. […] An alternative possible mechanism for eccentric-induced muscle dysfunction is based on the heterogeneity of sarcomere length and the length-tension relationship. […] The initial sequence of events underlying eccentric muscle dysfunction begins with the disruption of a sub-population of sarcomeres due to the heterogeneity of sarcomere length.

• #1 Cellular mechanism of eccentric-induced muscle injury and its relationship with sarcomere heterogeneity

  https://www.e-jer.org/journal/view.php?viewtype=pubreader&number=2013600137

  Activity-induced muscle injury and dysfunction have been identified as key components of musculoskeletal injuries. […] General features of eccentric-induced muscle injury are well documented and include disruption of intracellular muscle structure, prolonged muscle weakness and dysfunction, a delayed-onset muscle soreness, and inflammation. […] Possible mechanisms responsible for eccentric-induced muscle injury are activation impairment and structural disruption of the sarcomere. […] Therefore, the aim of this review is to focus attention particularly on the two main cellular mechanism of muscle cell injury following accustomed eccentric contraction. […] The first possible mechanism is a failure of Ca2+ release and up-take. […] The failure of EC coupling has been demonstrated after eccentric exercise, and it suggests that less calcium is released per action potential.

• #1 Pathophysiology of Skeletal Muscle Injury | Musculoskeletal Key

  https://musculoskeletalkey.com/pathophysiology-of-skeletal-muscle-injury/

  Factors related to an athletes risk of muscle injury include fatigue, conditioning, weakness, illness, age, gender, medications/drugs, and nutritional status. […] Underlying factors such as fatigue, weakness, and previous injury are often associated with muscle injury. […] Eccentric contraction is also often noted as a cause for muscle injury, and it has been suggested muscles that function primarily in an eccentric manner are at greater risk for injury. […] A second group of muscles noted to be at an increased risk of injury are those which function across two joints. […] The most commonly seen primary muscle injuries are muscle strains, which represent almost half of all athletic injuries. […] Contributing factors to strains are the magnitude of force applied, rate of force application, and the mechanical strength of the muscle unit being tested.

• #1

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8856841/

  Skeletal muscle healing follows a constant order, with no major changes depending on the cause (contusion, stretch or laceration). […] Three phases were identified in this process: destruction, repair, and remodeling. The last two phases (repair and remodeling) overlap and are closely related. […] Phase 1: destruction characterized by rupture and subsequent necrosis of myofibrils, by the formation of hematoma in the space formed between the ruptured muscle, and by the proliferation of inflammatory cells. […] Phase 2: repair and remodeling consists of the phagocytosis of the necrotic tissue, the regeneration of myofibrils, and the concomitant production of connective scar tissue, as well as vascular neoformation and neural growth. […] Phase 3: remodeling maturation period of regenerated myofibrils, contraction and reorganization of scar tissue, and recovery of muscle functional capacity.

• #1 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Since myofibrils are fusiform and very long, there is an imminent risk that the necrosis initiated at the site of the lesion extends throughout the length of the fiber. However, there is a specific structure, called a contraction band, which is a condensation of the cytoskeletal material that acts as an „antifire system”. […] Once the destruction phase decreases, the present repair of muscle injury begins with two simultaneous and competitive processes: the regeneration of the myofibril route and the formation of the scar connective tissue. A balanced progression of these processes is a prerequisite for optimal recovery of contractile muscle function. […] Although myofibrils are generally considered nonlytic, the regenerative capacity of skeletal muscle is guaranteed by an intrinsic mechanism that restores the injured contractile tract. During embryonic development, an undifferentiated cell reserve pool called satellite cells is stored below the basal lamina of each myofibril. In response to the lesion, these cells first proliferate, then differentiate into myofibrils, and finally join each other to form multinucleated myobribules.

• #1 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/

  During embryonic development, an undifferentiated cell reserve pool called satellite cells is stored below the basal lamina of each myofibril. In response to the lesion, these cells first proliferate, then differentiate into myofibrils, and finally join each other to form multinucleated myobribules. […] Over time, the formed scar decreases in size, leading the edges of the lesion to a greater grip with each other. […] However, it is not known whether the transection of the myofibrils from the opposite sides of the scar will definitely merge with each other or if it will form a septum of connective tissue between them. […] Immediately after the muscle injury, the interval formed between the rupture of muscle fibers is filled by hematoma. […] From the 1st day, inflammatory cells, including phagocytes, invade the hematoma and begin to organize the clot.

• #1

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8856841/

  Since myofibrils are fusiform and very long, there is an imminent risk that the necrosis initiated at the site of the lesion extends throughout the length of the fiber. However, there is a specific structure, called a contraction band, which is a condensation of the cytoskeletal material that acts as an „antifire system”. […] Once the destruction phase decreases, the present repair of muscle injury begins with two simultaneous and competitive processes: the regeneration of the myofibril route and the formation of the scar connective tissue. A balanced progression of these processes is a prerequisite for optimal recovery of contractile muscle function. […] Although myofibrils are generally considered nonlytic, the regenerative capacity of skeletal muscle is guaranteed by an intrinsic mechanism that restores the injured contractile tract. During embryonic development, an undifferentiated cell reserve pool called satellite cells is stored below the basal lamina of each myofibril. In response to the lesion, these cells first proliferate, then differentiate into myofibrils, and finally join each other to form multinucleated myobribules. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

• #1 MUSCLE INJURY – PHYSIOPATHOLOGY, DIAGNOSIS, TREATMENT AND CLINICAL PRESENTATION

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4799202/

  Phase 2: consists of repair and remodeling, with phagocytosis of the necrotic tissue, regeneration of the myofibrils and concomitant production of connective scar tissue, along with neoformation of vessels and neural growth. […] Phase 3: consists of remodeling, with maturation of the regenerated myofibrils, contraction and reorganization of the scar tissue and recovery of muscle functional capacity. […] Although the myofibrils are generically considered to be non-mitotic, the regenerative capacity of skeletal muscles is ensured by an intrinsic mechanism that restores the injured contractile apparatus. […] Immediately after the muscle injury, the gap formed by the tear in the muscle fibers is filled by a hematoma. […] The fibrin derived from blood and the fibronectin intercalate to form granulation tissue, which constitutes an initial frame for anchoring recruited fibroblasts to the site. […] One process that is vital for regenerating the injured muscle is the vascularization. Restoration of the vascular supply is the first sign of regeneration, and this is a prerequisite for subsequent morphological and functional recovery.

• #1 Understanding the 3 Phases of Muscle Healing – Athletico

  https://www.athletico.com/2017/03/27/understanding-the-3-phases-of-muscle-healing/

  During this important phase, a cell called a macrophage is introduced into the injured site. A macrophage eats and cleans away the dead tissue and dry blood caused by the injury. Once this is complete, another cell called a satellite cell is released into the injured area. Satellite cells transform into myoblast cells, which group together to create new muscle fibers. However, unlike a broken bone that is repaired by regenerating only new bone, an injured muscle is not replaced with only new muscle fibers. Another cell, called a fibroblast, also produces connective tissue at the injured site. It is a combination of connective tissue and muscle fibers that repair the injured muscle. In addition, new blood vessels and nerves generate during this phase. This repair phase commonly is peaking about two weeks after injury.

• #1 Azthena logo with the word Azthena

  https://www.news-medical.net/health/How-Do-Muscles-Repair-Themselves-After-Injury.aspx

  Muscle regeneration in response to injury typically initiates during the first week after injury, peaking at two weeks, and gradually slowing between three and four weeks. […] Resident muscle stem cells, also known as satellite cells, are located between the plasmalemma of myofiber on the basal lamina. These specialized cells possess a potential for muscle regeneration following injury. After muscles are injured, satellite cells become rapidly activated from a resting or quiescent state. […] In adult muscle cells, quiescent satellite cells express the box protein 7 (PAX7), on the activated cells upregulate myogenic regulatory factor MYOD and proliferate. When cells undergo differentiation into myocytes, most satellite cells downregulate PAX7 and maintain the expression of MYOD. This allows the cells to initiate the process of myogenesis via upregulating the protein myogenin.

• #1 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Approximately 10 days after the trauma, the maturation of the scar reaches a point in which it is no longer the most fragile site of the muscle injury. […] Although most skeletal muscle lesions heal without the formation of disabling fibrous scar tissue, fibroblast proliferation may be excessive, resulting in the formation of dense scar tissue within the muscle lesion. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

• #1 Muscle Strains: Causes, Symptoms, Treatment & Recovery

  https://my.clevelandclinic.org/health/diseases/22336-muscle-strains

  Muscle strains can be mild to severe. A grade 1 muscle strain only pulls and breaks a few fibers. But a grade 3 muscle strain tears all the way through. […] A muscle strain, or pulled muscle, is a tear in your muscle fibers. Its one of the most common soft tissue injuries. You can strain a muscle by pulling it too hard or using it too much, which weakens the fibers. […] When you strain a muscle, the strands of fiber are stretched beyond their limit and tear apart. […] Muscle strains happen when you tear the fibers of your muscle. This can happen suddenly or gradually. […] Common causes of muscle strains include: Acute injuries. Muscle strains are often sports injuries, caused by sudden sprinting, twisting or jumping. But accidental muscle strains are also common in everyday life. […] Healthcare providers also grade muscle strains by how severe they are.

• #1 Physical Therapy & Occupational Therapy in Chicago for Muscle Injury – Strains

  https://www.physiopartners.com/Injuries-Conditions/Muscle-Injury/Muscle-Injury-Issues/Muscle-Strains/a~8609/article.html

  Muscle strains occur when a muscle in your body is overstretched or overworked. […] A muscle strain can occur in any of your voluntary muscles (or tendons which attach to the muscle), but they are most common in the low back, the calves, the front and back of the thighs, the pectoral muscles, and the muscles of the neck and the shoulder. Muscle strains occur more often in muscles that cross two joints (such as the thigh or calf muscles) and often occur when the muscles are working eccentrically (working while under a stretch). […] A muscle strain can occur due to a one-time overstretching or overworking of a muscle (acute injury) or can occur from repetitive use of a muscle over time (overuse injury). […] All muscle strains include tearing of some muscle fibers: Grade I (mild): Very few muscle fibers have been injured.

• #1 Muscle Strains: Causes, Symptoms, Treatment & Recovery

  https://my.clevelandclinic.org/health/diseases/22336-muscle-strains

  If you have a severe muscle strain, your muscle has torn all the way through. A complete muscle tear (muscle rupture) might need surgery to repair it. […] Most people can recover from a pulled muscle at home. Only a severe, grade III tear might need surgery. […] If you only have a minor (grade I) muscle strain, it should heal within a few weeks. Moderate (grade II) muscle strains may take several weeks to months to heal completely. A severe (grade III) muscle strain can take four to six months to heal after surgery.

• #1 Physical Therapy & Occupational Therapy in Chicago for Muscle Injury – Strains

  https://www.physiopartners.com/Injuries-Conditions/Muscle-Injury/Muscle-Injury-Issues/Muscle-Strains/a~8609/article.html

  Grade II (moderate): A large category including all strains between a grade I and grade III. […] Grade III (severe): All fibers of the muscle are completely torn. […] The initial aim of treatment for acute muscle strains at PhysioPartners is to decrease the pain as well as any secondary inflammation in the area. […] Some initial inflammation is actually required to start the healing process, but a large inflammatory response can also lead to secondary inflammation and secondary cell injury, which affects tissues that were not directly related to the initial insult. […] Once the initial pain and inflammation has calmed down, your Physical Therapist Occupational Therapist will focus on improving the flexibility and strength of the involved muscle. […] Eccentric exercises are ones that put load through your muscle as it is lengthening.

• #1 Musculoskeletal sprains and strains – Symptoms, diagnosis and treatment | BMJ Best Practice

  https://bestpractice.bmj.com/topics/en-gb/578

  Muscle injuries occur from either direct or indirect trauma. […] Predisposing factors include type of muscle architecture (i.e., pennate muscle, type II fast twitch muscle fibres, muscle-tendon units that span 2 joints), previous injury, and inadequate warm-up before exercise. […] Eccentric contraction (i.e., muscle contraction associated with forcible lengthening of the contracting muscle, such as when lowering a weight or pitching a ball) causes more frequent injury. […] In strains, an excessive tensile force subjected onto the muscle leads to the overstraining of the myofibres and consequently to a rupture near the musculotendinous junction. […] Muscle strains typically concern the superficial muscles working across 2 joints, such as the rectus femoris, semitendinosus, and gastrocnemius muscles. […] Muscle strain usually occurs in eccentric exercise. In eccentric exercise the contracting muscle is forcibly lengthened; in concentric exercise it shortens. While concentric contractions initiate movements, eccentric contractions slow or stop them (e.g., when lowering a weight).

• #1 Acute muscle injuries, what are they and how to manage them

  https://www.ibphysio.com.au/acute-muscle-injuries/

  Acute muscle injuries or strains and tears are one of the most common injuries seen in sport. The mechanism of injury usually involves a sudden acceleration or deceleration force during which the muscle fibers fail to cope with load demands of the task. […] Inadequate warm up, decreased joint range, muscle tightness, fatigue, previous injury, muscle imbalance, technique and spinal problems can all predispose the muscle to injury. […] Muscle injuries are classified into 3 grades. These grades help to direct the rehabilitation program and predict the healing time of the injury. […] Muscles heal through 3 phases. […] During the initial phase of an acute muscle injury, pain, bleeding and swelling are at their worst. […] During this stage, the body starts to lay down new tissue into the area of damage, including regeneration of new muscle fibers and production of connective scar tissue.

• #1

  https://journals.lww.com/cjsportsmed/fulltext/2023/05000/mechanisms_of_hamstring_injury_in_professional.3.aspx

  The injuries may combine biomechanical characteristics from both sprinting and stretching-type mechanisms. […] Therefore, in our opinion also, mixed-type injury mechanisms can occur in hamstring injuries. […] In addition to sprinting and stretching, we described the mixed-type injury mechanism, which included typical patterns from both of these mechanisms. […] Most cases (93%) involved knee flexion 45 degrees, and in 6 of the cases, we found the fully extended knee. […] Hip and trunk flexion were also typical biomechanical factors associated with hamstring injury. […] The stretch-type injuries usually occur during a side or sagittal split movement, high kick, or stretching. […] In our sample, of the 5 stretch-type injuries (36% of all injuries), 2 affected SM, 2 were proximal avulsions (BF + ST), and 1 affected distal BF.

• #1 Quadriceps injury | Radiology Reference Article | Radiopaedia.org

  https://radiopaedia.org/articles/quadriceps-injury?lang=us

  Quadriceps injuries are common injuries in athletes and the quadriceps muscle is often affected by muscle strains in situations requiring explosive movements as seen in certain sports 1-3. […] The injury mechanism varies with the type of injury. Muscle contusions and crush injuries are caused by direct trauma 3. Proximal tendon tears or tendon avulsion injuries, myotendinous and myofascial strain injuries are usually caused by eccentric loading mechanisms. Quadriceps tendinosis is a typical overuse injury and quadriceps tendon rupture can be caused by both eccentric loading or direct impact 3,4. […] Most quadriceps tendon strain injuries concern the rectus femoris muscle. It crosses two joints, features fast-twitching (type II) fibers and complex musculotendinous anatomy and undergoes forceful eccentric contraction during sprinting, jumping and kicking 2,3.

• #1 Medial Gastrocnemius Strain: Practice Essentials, Epidemiology, Functional Anatomy

  https://emedicine.medscape.com/article/91687-overview

  A medial calf injury is a musculotendinous disruption of varying degrees in the medial head of the gastrocnemius muscle that results from an acute, forceful push-off with the foot. […] One mechanism that occurs is on the back leg during a lunging shot, in which the knee is extended while the foot is dorsiflexed. This action puts maximal tension on the gastrocnemius muscle as the lengthened muscle is contracted at the „push off,” resulting in a medial calf injury. […] The medial calf injury usually occurs when an eccentric force is applied to the gastrocnemius muscle, which usually happens when the knee is extended, the ankle is dorsiflexed, and the gastrocnemius attempts to contract in the already lengthened state. […] As indicated in the Practice Essentials section, medial calf injuries occur more commonly in the middle-aged recreational athlete.

• #1 Physical Therapy & Occupational Therapy in Chicago for Muscle Injury – Strains

  https://www.physiopartners.com/Injuries-Conditions/Muscle-Injury/Muscle-Injury-Issues/Muscle-Strains/a~8609/article.html

  These types of exercises are necessary as part of your rehabilitation program in order to prepare the strained muscle for the return to normal everyday activity and sport. […] The most common complication with a muscle strain is a re-injury which most often results from returning to activity too soon before the tear is healed. […] In more severe strains, hematomas (blood clots) can develop as a complication within the healing muscle. […] Another complication of severe muscle strains can be a compartment syndrome. […] A severe muscle strain may also result in a much less common, but serious, complication call rhabdomyolysis. […] Muscle strains involve a tear to the fibers of a muscle and vary in healing time depending on how severe the strain is.

• #1 A Novel Muscle Atrophy Mechanism: Myocyte Degeneration Due to Intracellular Iron Deprivation

  https://www.mdpi.com/2073-4409/11/18/2853

  Muscle atrophy is defined as the progressive degeneration or shrinkage of myocytes and is triggered by factors such as aging, cancer, injury, inflammation, and immobilization. […] Although the detrimental effects of iron overload or iron deficiency on muscle function have been studied, the molecular mechanism of iron-dependent muscle atrophy has not been elucidated. […] Our study revealed that the lower iron concentration in injured muscle was associated with the upregulation of ferroportin, an iron exporter that transports iron out of cells. […] Iron deprivation caused myocyte loss and a marked depletion of mitochondrial membrane potential leading to muscle atrophy, together with increased levels of myostatin, the upstream regulator of atrogin1 and muscle RING-finger protein-1 (MuRF1).

• #1

  https://journal.aspetar.com/en/archive/volume-2-issue-3/definition-of-acute-muscle-injury-what-have-we-learnt

  The musculotendinous junction, the weakest link within the muscle tendon unit, is the most vulnerable site in indirect strain injuries. When muscle tension increases suddenly, as it occurs in eccentric contractions, the damage is in the area beneath the epimysium and the site of muscle attachment to the periosteum. […] Disruptions in the fibres cause biochemical changes both from direct injury to the fibres and from the inflammatory reaction. […] Released in response to an insult, serum creatine kinase and lactate dehydrogenase enzyme levels are indirect markers of muscle damage after eccentric exercise. Inflammatory reactions also occur. Acute inflammation protects, localises and removes injurious agents from the body and promotes healing and repair. […] The acute phase of inflammation lasts up to 3 to 4 days after the initial insult. Proliferation of fibroblasts, increased collagen production and degradation of mature collagen weaken the tissue.

• #1

  https://he05.tci-thaijo.org/index.php/CMJ/article/view/249

  Eccentric contraction exercise causes more muscle injury and damage than concentric exercise. The mechanism of muscle damage is divided into primary and secondary damages. One of the importance sources of secondary damage is derived from reactive oxygen species (ROS), which an increase of ROS results in the destruction of muscle tissue. […] Antioxidant has been illustrated as molecules that control the adverse effect from ROS-induced muscle damage. An improved antioxidant level is believed to be a beneficial aspect against oxidative stress which develops from adaptation through exercise training. […] Besides, the responsiveness of free radicals and antioxidants to eccentric exercise also depends on the intensity and duration of exercise.

• #1 Should You Stretch A Muscle Strain? — Physio Network

  https://www.physio-network.com/blog/stretch-muscle-strain/

  Muscle tears occur when the force applied to the tissue generates greater stress or strain than the tissue can withstand. This damages the myofibrils (muscle fibers) as a result of rapid eccentric (lengthening) contractions, often during acceleration or deceleration movements. […] To stretch a muscle strain would appear to repeat the mechanism of injury and increase the potential to further damage an already weakened area. Therefore, by acknowledging that strains occur through loading muscle fibers beyond their capacity, it allows us to determine that immediately stretching/loading again would likely be disadvantageous. […] Irrespective of classification, all muscle strains go through this process. It is the speed at which this occurs which will change depending on the severity of injury.

• #1 Sports-related lower limb muscle injuries: pattern recognition approach and MRI review | Insights into Imaging | Full Text

  https://insightsimaging.springeropen.com/articles/10.1186/s13244-020-00912-4

  The optimal timing of MRI following lower limb muscle injury has not been defined and has been mainly based on expert opinions. […] Connective tissue involvement is related to prolonged return to sport, particularly if it is a central or proximal tendon (free tendon) or near the tendon origin, and especially if there is retraction or loss of tension.

• #2 Should You Stretch A Muscle Strain? — Physio Network

  https://www.physio-network.com/blog/stretch-muscle-strain/

  Muscle tears occur when the force applied to the tissue generates greater stress or strain than the tissue can withstand. This damages the myofibrils (muscle fibers) as a result of rapid eccentric (lengthening) contractions, often during acceleration or deceleration movements. […] To stretch a muscle strain would appear to repeat the mechanism of injury and increase the potential to further damage an already weakened area. Therefore, by acknowledging that strains occur through loading muscle fibers beyond their capacity, it allows us to determine that immediately stretching/loading again would likely be disadvantageous. […] Irrespective of classification, all muscle strains go through this process. It is the speed at which this occurs which will change depending on the severity of injury.

• #2 The mechanism of hamstring injuries – a systematic review | BMC Musculoskeletal Disorders | Full Text

  https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/s12891-020-03658-8

  Injuries to the hamstring muscles are among the most common in sports and account for significant time loss. Despite being so common, the injury mechanism of hamstring injuries remains to be determined. […] All studies that reported the stretch-type injury mechanism concluded that injury occurs due to extensive hip flexion with a hyperextended knee. The vast majority of studies on injuries during running proposed that these injuries occur during the late swing phase of the running gait cycle. […] A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle. […] All the studies of stretch-type injuries concluded that injuries occur due to extensive hip flexion with simultaneous knee extension.

• #2

  https://journals.lww.com/cjsportsmed/fulltext/2023/05000/mechanisms_of_hamstring_injury_in_professional.3.aspx

  To describe the injury mechanisms and magnetic resonance imaging (MRI) findings in acute hamstring injuries of male soccer players using a systematic video analysis. […] Two different hamstring injury mechanisms have been previously described in the literature: stretching-type and sprinting-type. […] The stretching-type hamstring injury has been shown to most commonly affect the proximal tendon of the semimembranosus (SM) or biceps femoris (BF). […] By contrast, the sprinting-type hamstring injury most often affects the long head of the BF, whereas the most severe avulsions of BF, SM, and/or semitendinosus (ST) usually occur as a result of a rapid forceful hip flexion with the ipsilateral knee in extension. […] However, in certain cases, the hamstring injury mechanisms are not so easily classifiable, as the injury inciting actions may involve different movements that make hamstrings susceptible to injury.

• #2 Cellular mechanism of eccentric-induced muscle injury and its relationship with sarcomere heterogeneity

  https://www.e-jer.org/journal/view.php?viewtype=pubreader&number=2013600137

  Activity-induced muscle injury and dysfunction have been identified as key components of musculoskeletal injuries. […] General features of eccentric-induced muscle injury are well documented and include disruption of intracellular muscle structure, prolonged muscle weakness and dysfunction, a delayed-onset muscle soreness, and inflammation. […] Possible mechanisms responsible for eccentric-induced muscle injury are activation impairment and structural disruption of the sarcomere. […] Therefore, the aim of this review is to focus attention particularly on the two main cellular mechanism of muscle cell injury following accustomed eccentric contraction. […] The first possible mechanism is a failure of Ca2+ release and up-take. […] The failure of EC coupling has been demonstrated after eccentric exercise, and it suggests that less calcium is released per action potential.

• #2 Cellular mechanism of eccentric-induced muscle injury and its relationship with sarcomere heterogeneity

  https://www.e-jer.org/journal/view.php?viewtype=pubreader&number=2013600137

  The possible failure sites in the EC coupling pathway are, the sarcolemma, the t-tubule, the DHPR, the linkage between the DHPR and the RyR, the RyR, and the SR. […] An alternative possible mechanism for eccentric-induced muscle dysfunction is based on the heterogeneity of sarcomere length and the length-tension relationship. […] The popping sarcomere hypothesis assumes the presence of irregular sarcomere lengths. […] The initial sequence of events underlying eccentric muscle dysfunction begins with the disruption of a sub-population of sarcomeres due to the heterogeneity of sarcomere length. […] All of this produces an increase in intracellular Ca2+ levels which triggers proteolysis associated and fiber breakdown.

• #2 Pathophysiology of Skeletal Muscle Injury | Musculoskeletal Key

  https://musculoskeletalkey.com/pathophysiology-of-skeletal-muscle-injury/

  Factors related to an athletes risk of muscle injury include fatigue, conditioning, weakness, illness, age, gender, medications/drugs, and nutritional status. […] Underlying factors such as fatigue, weakness, and previous injury are often associated with muscle injury. […] Eccentric contraction is also often noted as a cause for muscle injury, and it has been suggested muscles that function primarily in an eccentric manner are at greater risk for injury. […] A second group of muscles noted to be at an increased risk of injury are those which function across two joints. […] The most commonly seen primary muscle injuries are muscle strains, which represent almost half of all athletic injuries. […] Contributing factors to strains are the magnitude of force applied, rate of force application, and the mechanical strength of the muscle unit being tested.

• #2 Acute muscle injuries, what are they and how to manage them

  https://www.ibphysio.com.au/acute-muscle-injuries/

  Acute muscle injuries or strains and tears are one of the most common injuries seen in sport. The mechanism of injury usually involves a sudden acceleration or deceleration force during which the muscle fibers fail to cope with load demands of the task. […] Inadequate warm up, decreased joint range, muscle tightness, fatigue, previous injury, muscle imbalance, technique and spinal problems can all predispose the muscle to injury. […] Muscle injuries are classified into 3 grades. These grades help to direct the rehabilitation program and predict the healing time of the injury. […] Muscles heal through 3 phases. […] During the initial phase of an acute muscle injury, pain, bleeding and swelling are at their worst. […] During this stage, the body starts to lay down new tissue into the area of damage, including regeneration of new muscle fibers and production of connective scar tissue.

• #2 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Skeletal muscle healing follows a constant order, with no major changes depending on the cause (contusion, stretch or laceration). […] Three phases were identified in this process: destruction, repair, and remodeling. The last two phases (repair and remodeling) overlap and are closely related. […] Phase 1: destruction – characterized by rupture and subsequent necrosis of myofibrils, by the formation of hematoma in the space formed between the ruptured muscle, and by the proliferation of inflammatory cells. […] Phase 2: repair and remodeling – consists of the phagocytosis of the necrotic tissue, the regeneration of myofibrils, and the concomitant production of connective scar tissue, as well as vascular neoformation and neural growth. […] Phase 3: remodeling – maturation period of regenerated myofibrils, contraction and reorganization of scar tissue, and recovery of muscle functional capacity.

• #2 MUSCLE INJURY – PHYSIOPATHOLOGY, DIAGNOSIS, TREATMENT AND CLINICAL PRESENTATION

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4799202/

  Muscle injuries can be caused by bruising, spraining or laceration. […] The tensile force exerted on a muscle may lead to excessive stretching of the muscle fibers and consequently a tear close to the muscle-tendon junction. Muscle sprains are typically observed in the superficial muscles that work by traversing two joints, such as the rectus femoris, semitendinosus and gastrocnemius muscles. […] Healing of skeletal muscles follows a constant order, without significant changes according to the cause (bruising, spraining or laceration). […] Three phases have been identified in this process: destruction, repair and remodeling. The last two of these phases (repair and remodeling) overlap and are closely interrelated. […] Phase 1: consists of destruction and is characterized by tearing and subsequent necrosis of myofibrils, formation of a hematoma in the space created in the torn muscle and proliferation of inflammatory cells.

• #2 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/

  Since myofibrils are fusiform and very long, there is an imminent risk that the necrosis initiated at the site of the lesion extends throughout the length of the fiber. […] However, there is a specific structure, called a contraction band, which is a condensation of the cytoskeletal material that acts as an „antifire system”. […] Once the destruction phase decreases, the present repair of muscle injury begins with two simultaneous and competitive processes: the regeneration of the myofibril route and the formation of the scar connective tissue. A balanced progression of these processes is a prerequisite for optimal recovery of contractile muscle function. […] Although myofibrils are generally considered nonlytic, the regenerative capacity of skeletal muscle is guaranteed by an intrinsic mechanism that restores the injured contractile tract.

• #2 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Over time, the formed scar decreases in size, leading the edges of the lesion to a greater grip with each other. However, it is not known whether the transection of the myofibrils from the opposite sides of the scar will definitely merge with each other or if it will form a septum of connective tissue between them. […] Immediately after the muscle injury, the interval formed between the rupture of muscle fibers is filled by hematoma. From the 1st day, inflammatory cells, including phagocytes, invade the hematoma and begin to organize the clot. […] Blood-derived fibrin and fibronectin intersperse to form granulation tissue, an initial frame and anchoring of the site for the recruited fibroblasts. More importantly, this new formed fabric provides the property of initial tension to resist the contractions applied against it.

• #2 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Since myofibrils are fusiform and very long, there is an imminent risk that the necrosis initiated at the site of the lesion extends throughout the length of the fiber. However, there is a specific structure, called a contraction band, which is a condensation of the cytoskeletal material that acts as an „antifire system”. […] Once the destruction phase decreases, the present repair of muscle injury begins with two simultaneous and competitive processes: the regeneration of the myofibril route and the formation of the scar connective tissue. A balanced progression of these processes is a prerequisite for optimal recovery of contractile muscle function. […] Although myofibrils are generally considered nonlytic, the regenerative capacity of skeletal muscle is guaranteed by an intrinsic mechanism that restores the injured contractile tract. During embryonic development, an undifferentiated cell reserve pool called satellite cells is stored below the basal lamina of each myofibril. In response to the lesion, these cells first proliferate, then differentiate into myofibrils, and finally join each other to form multinucleated myobribules.

• #2 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/

  Blood-derived fibrin and fibronectin intersperse to form granulation tissue, an initial frame and anchoring of the site for the recruited fibroblasts. […] More importantly, this new formed fabric provides the property of initial tension to resist the contractions applied against it. […] Approximately 10 days after the trauma, the maturation of the scar reaches a point in which it is no longer the most fragile site of the muscle injury. […] Although most skeletal muscle lesions heal without the formation of disabling fibrous scar tissue, fibroblast proliferation may be excessive, resulting in the formation of dense scar tissue within the muscle lesion. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

• #2 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Approximately 10 days after the trauma, the maturation of the scar reaches a point in which it is no longer the most fragile site of the muscle injury. […] Although most skeletal muscle lesions heal without the formation of disabling fibrous scar tissue, fibroblast proliferation may be excessive, resulting in the formation of dense scar tissue within the muscle lesion. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

• #2 Azthena logo with the word Azthena

  https://www.news-medical.net/health/How-Do-Muscles-Repair-Themselves-After-Injury.aspx

  Muscle regeneration in response to injury typically initiates during the first week after injury, peaking at two weeks, and gradually slowing between three and four weeks. […] Resident muscle stem cells, also known as satellite cells, are located between the plasmalemma of myofiber on the basal lamina. These specialized cells possess a potential for muscle regeneration following injury. After muscles are injured, satellite cells become rapidly activated from a resting or quiescent state. […] In adult muscle cells, quiescent satellite cells express the box protein 7 (PAX7), on the activated cells upregulate myogenic regulatory factor MYOD and proliferate. When cells undergo differentiation into myocytes, most satellite cells downregulate PAX7 and maintain the expression of MYOD. This allows the cells to initiate the process of myogenesis via upregulating the protein myogenin.

• #2 Azthena logo with the word Azthena

  https://www.news-medical.net/health/How-Do-Muscles-Repair-Themselves-After-Injury.aspx

  More recently than this, researchers have discovered a previously unidentified repair mechanism that is triggered after muscle injury. Researchers demonstrated a repair process that is independent of muscle stem cells (cell-autonomous) after using mouse models. […] This finding challenges the skeletal muscle and homeostasis and regeneration dogma which is widely assumed to be mediated by satellite cells. The work opposes this stem cell-centric view, demonstrating that muscle integrity is also maintained through an alternative myofibre autonomous repair mechanism. At the heart of this mechanism is a nuclear migration for local delivery of messenger RNA is required for the production of protein and repair of damaged sarcomeres.

• #2

  https://journal.aspetar.com/en/archive/volume-2-issue-3/definition-of-acute-muscle-injury-what-have-we-learnt

  When the inflammatory phase subsides, repair is started and continues for 2 to 3 weeks. […] The final stage of healing is maturation and remodelling of collagen, occurring from 2 to 3 weeks after the insult, until patients are pain-free. […] The overall goal is to assist and respect the body with its natural healing processes. Therefore, the athletic trainer must not return the athlete to activity too soon. […] When collagen is formed, it must be appropriately stressed in the normal lines of tension. […] This stage presents at about 2 to 3 weeks after injury and is characterised by the absence of inflammation. […] The severity of the muscular and musculotendinous injuries is classified according to a 3-grade classification system from MRI and US. […] Clinical assessment, site of injury and pathophysiology can all provide prognostic information regarding rehabilitation and recovery time after an acute muscle strain injury.

• #2 Overview of Sprains and Other Soft-Tissue Injuries – Injuries; Poisoning – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/injuries-poisoning/sprains-and-other-soft-tissue-injuries/overview-of-sprains-and-other-soft-tissue-injuries

  Tears in ligaments or muscles may be graded as 1st degree: Minimal (fibers are stretched but intact, or only a few fibers are torn) […] 2nd degree: Partial (some to almost all fibers are torn) […] 3rd degree: Complete (all fibers are torn). […] Tendon tears can be partial or complete. With complete tears, the motion produced by the detached muscle is usually lost. Partial tears can result from a single traumatic event (eg, penetrating trauma) or repeated stress (chronically, causing tendinopathy). Motion is often intact, but partial tears may progress to complete tears, particularly when significant or repetitive force is applied. […] Many partial tears in ligaments, tendons, or muscles heal spontaneously. Complete tears often require surgery to restore anatomy and function. Prognosis and treatment vary greatly depending on the location and severity of the injury.

• #2 Sprains and Strains Meaning, Causes, First Aid, Treatment

  https://www.medicinenet.com/sprained_ankle/article.htm

  Strains are described by the severity of damage in three grades: Grade 1 strain usually causes stretching of a few of the muscle fibers. Grade 2 strain has more significant damage, and some muscle fibers are damaged or torn. Grade 3 strain is a complete rupture of the muscle. […] Usually, the mechanism of injury involves placing the muscle-tendon unit or the ligament under excessive stretching, causing damage to the muscle, tendon, or ligament fibers.

• #2 Physical therapy in our clinic for Muscle Injury – Strains

  https://www.rmts.clinic/Injuries-Conditions/Muscle-Injury/Muscle-Injury-Issues/Muscle-Strains/a~8609/article.html

  Muscle strains occur when a muscle in your body is overstretched or overworked. […] A muscle strain can occur in any of your voluntary muscles (or tendons which attach to the muscle), but they are most common in the low back, the calves, the front and back of the thighs, the pectoral muscles, and the muscles of the neck and the shoulder. Muscle strains occur more often in muscles that cross two joints (such as the thigh or calf muscles) and often occur when the muscles are working eccentrically (working while under a stretch). […] A muscle strain can occur due to a one-time overstretching or overworking of a muscle (acute injury) or can occur from repetitive use of a muscle over time (overuse injury). […] There are several classification systems developed and in use regarding muscle strains but the most commonly used system includes three grades. All muscle strains include tearing of some muscle fibers: Grade I (mild): Very few muscle fibers have been injured. […] Grade II (moderate): A large category including all strains between a grade I and grade III. […] Grade III (severe): All fibers of the muscle are completely torn.

• #2

  https://www.smjrscorp.com/blog/torn-muscle-vs-pulled-muscle-what-s-the-difference

  Muscle strains, specifically, occur when the muscle fibers are overstretched or torn, commonly classified as mild, moderate, or severe based on the extent of the damage. […] Torn muscles are classified into three grades: Grade I represents mild tears with minimal fiber damage, Grade II denotes moderate tears with partial disruption, and Grade III signifies severe tears that result in a complete rupture and significant loss of function. […] A pulled muscle, or muscle strain, occurs when muscle fibers are overstretched or partially torn, often due to sudden movements or excessive stress. […] Understanding the differences between torn muscles and strained muscles is crucial for effective injury management. […] Torn muscles involve a partial or complete rupture of muscle fibers, which are classified into three grades (Grade I, II, and III). In contrast, strained muscles typically represent mild to moderate overstretching without complete tearing. […] Torn muscles often lead to significant loss of function and strength, while strained muscles usually allow for some mobility, albeit with discomfort and movement limitations.

• #2 Physical therapy in our clinic for Muscle Injury – Strains

  https://www.rmts.clinic/Injuries-Conditions/Muscle-Injury/Muscle-Injury-Issues/Muscle-Strains/a~8609/article.html

  Several symptoms can indicate that you have incurred a muscle strain but the symptoms you feel will depend on the grade of strain you have incurred: sudden onset of pain, or pain/soreness that comes on the next day related to a specific event; pain on touching the injured area; mild, moderate, or severely limited range of movement, or an extreme abnormal range of motion; decreased strength in the injured muscle; bruising or discoloration in the area or at a distal location to the strain; swelling; a „knotted up” feeling; a local divot or bump in the affected area due to the torn muscle fibers; muscle spasm in the area; stiffness in the area. […] Your physical therapist at Rocky Mountain Therapy Services will ask a number of questions to determine if you have strained your muscle and to determine how severe the damage is. […] After a thorough history and physical examination your physical therapist will determine the grade of your muscle strain.

• #2 Physical Therapy & Occupational Therapy in Chicago for Muscle Injury – Strains

  https://www.physiopartners.com/Injuries-Conditions/Muscle-Injury/Muscle-Injury-Issues/Muscle-Strains/a~8609/article.html

  Grade II (moderate): A large category including all strains between a grade I and grade III. […] Grade III (severe): All fibers of the muscle are completely torn. […] The initial aim of treatment for acute muscle strains at PhysioPartners is to decrease the pain as well as any secondary inflammation in the area. […] Some initial inflammation is actually required to start the healing process, but a large inflammatory response can also lead to secondary inflammation and secondary cell injury, which affects tissues that were not directly related to the initial insult. […] Once the initial pain and inflammation has calmed down, your Physical Therapist Occupational Therapist will focus on improving the flexibility and strength of the involved muscle. […] Eccentric exercises are ones that put load through your muscle as it is lengthening.

• #2 Hamstring Muscle Injuries – OrthoInfo – AAOS

  https://orthoinfo.aaos.org/en/diseases–conditions/hamstring-muscle-injuries/

  Like strains, hamstring tendon avulsions are also caused by large, sudden loads. […] Muscle tightness. Tight muscles are vulnerable to strain. Athletes should follow a year-round program of daily stretching exercises. […] Muscle imbalance. When one muscle group is much stronger than its opposing muscle group, the imbalance can lead to a strain. This frequently happens with the hamstring muscles. […] Hamstring strains occur more often in adolescents because bones and muscles do not grow at the same rate. During a growth spurt, a child’s bones may grow faster than the muscles. The growing bone pulls the muscle tight. A sudden jump, stretch, or impact can tear the muscle away from its connection to the bone. […] Treatment of hamstring strains depends on the type of injury you have, its severity, and your own needs and expectations.

• #2 Musculoskeletal sprains and strains – Symptoms, diagnosis and treatment | BMJ Best Practice US

  https://bestpractice.bmj.com/topics/en-us/578

  Muscle injuries occur from either direct or indirect trauma. […] Predisposing factors include type of muscle architecture (i.e., pennate muscle, type II fast twitch muscle fibers, muscle-tendon units that span 2 joints), previous injury, and inadequate warm-up before exercise. […] Eccentric contraction (i.e., muscle contraction associated with forcible lengthening of the contracting muscle, such as when lowering a weight or pitching a ball) causes more frequent injury. […] In strains, an excessive tensile force subjected onto the muscle leads to the overstraining of the myofibers and consequently to a rupture near the musculotendinous junction. […] Muscle strains typically concern the superficial muscles working across 2 joints, such as the rectus femoris, semitendinosus, and gastrocnemius muscles. […] Muscle strain usually occurs in eccentric exercise. […] In eccentric exercise the contracting muscle is forcibly lengthened; in concentric exercise it shortens. […] While concentric contractions initiate movements, eccentric contractions slow or stop them (e.g., when lowering a weight).

• #2 How to Prevent Muscle Strains • Stronger by Science

  https://www.strongerbyscience.com/how-to-prevent-muscle-strains/

  If you have a complete muscle tear, you’ll know it. A telltale sign of a complete tear is an audible pop, along with a tearing sensation. […] The strongest predictor of injury is history of previous muscle injury. […] Fatigue, both of the muscle as well as the central nervous system, also plays an important role in strain injury. […] Because muscle strain injuries often occur at the musculotendinous junction, tendon strength is another key determinant of injury risk.

• #2 Explorations in Hamstring Injury Concepts – Part II: Mechanism of Injury

  https://www.linkedin.com/pulse/explorations-hamstring-injury-concepts-part-ii-ryan

  The second, given by Sam Blanchard in his talk on using research in hamstring rehab, discusses the theory that these types of injuries occur in either the stride or stance phase, more specifically during the amortization phase wherein the hamstring muscle switches from eccentric to concentric contraction. […] Regardless of the differences in either frame of thinking, each requires an inherent understanding of high-speed running. […] When analyzing forces that our hamstrings are subjected to during each of these phases, it has been determined that peak forces between the two phases are similar (Chumanov et al., 2007). However, in the period of terminal swing, or the last portion of the swing phase shortly before our heel touches the ground and begins the stance phase, we most often see these types of high-speed running injuries even though forces are similar.

• #2

  https://journals.lww.com/cjsportsmed/fulltext/2023/05000/mechanisms_of_hamstring_injury_in_professional.3.aspx

  All of the stretch-related injuries occurred during a rapid change of movement involving hip flexion and knee extension. […] The 6 mixed-type injuries involved high-speed running or acceleration combined with stretch-related movement (lunging, landing, or kicking), and the injury locations varied widely: 2 proximal BFs, proximal 2 tendon avulsions (BF + ST), mid-thigh SM, distal BF, and distal ST. […] Rapid movements involving both sprinting and stretching can be very difficult to identify based on only real-time eye witness or athlete’s own recollection. […] If the injury moment is captured on video, the video analysis with slow motion and video stoppage enables specific and detailed assessment of injury mechanism. […] In summary, video analysis is a helpful tool for a physician in understanding injury mechanisms and their relation to types of hamstring injury.

• #2 Thigh strain

  https://fittoplay.org/body-parts/hamstring/thigh-strain/

  A thigh (quadriceps) strain is a very common sports injury. Thigh strains are common in sports such as football, and there are more players sidelined due to this injury, compared to strains in the hamstrings or groin. Some factors might potentially increase the risk of injury: Muscle weakness or a difference in the strength of the quadriceps in relation to the hamstrings. In football, thigh strains often occur when the player is slowing down (decelerating) after a sprint, either because they are taking too small or too large steps. This injury can also occur when an athlete sprints, jumps, or kicks. Type 2 injuries have a longer rehabilitation period and a poorer prognosis, compared to type 1 injuries. A common sign of a distal strain injury is an acute pain in the affected area during activities that require powerful contractions of the muscle. If the strain is severe enough, the muscle may be torn completely in two. Total ruptures recover well without surgery and there are usually no long-term complications. Anti-inflammatory medications (NSAIDs), such as Voltaren and Neurofen, are not recommended as they can hinder the body’s natural healing processes. Re-injury is not uncommon. It is, therefore, important that the athlete continues with rehabilitation exercises long after they have returned to the sport. This will minimise the risk of re-injury.

• #2 Medial Gastrocnemius Strain: Practice Essentials, Epidemiology, Functional Anatomy

  https://emedicine.medscape.com/article/91687-overview

  The cold and unstretched muscles that recreational athletes often use to compete with are very likely to rupture when challenged compared with conditioned and stretched muscles. […] The athlete with recurrent calf strains is likely to have healed with fibrotic scar tissue, which absorbs forces differently and is thus more likely to result in rupture when the muscle is challenged.

• #2 Overview of Sprains and Other Soft-Tissue Injuries – Injuries; Poisoning – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/injuries-poisoning/sprains-and-other-soft-tissue-injuries/overview-of-sprains-and-other-soft-tissue-injuries

  Serious complications of sprains, strains, and tendon injuries are unusual but may cause permanent limb dysfunction. […] Compartment syndrome threatens limb viability (possibly requiring amputation) and survival. […] Various ligament injuries, particularly 3rd-degree sprains, can lead to joint instability. Instability can be disabling and increases the risk of osteoarthritis. […] Injuries that result in joint instability predispose to repeated joint stresses that can damage joint cartilage and result in osteoarthritis. […] Many 3rd-degree sprains and tendon tears require surgical repair.

• #2 A Novel Muscle Atrophy Mechanism: Myocyte Degeneration Due to Intracellular Iron Deprivation

  https://www.mdpi.com/2073-4409/11/18/2853

  Myostatin expression under iron deficiency was mediated by an orphan nuclear receptor, dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome (DAX1). […] We examined the correlation between muscle atrophy and myocyte iron concentration by comparing iron levels in torn (injured) muscle and intact (control) muscle. […] These results indicate that decreased iron levels due to muscle injury are associated with the upregulation of ferroportin expression in myocytes. […] Taken together, these results suggest that muscle injury-induced hypoxic conditions regulate ferroportin expression through direct activation of HIF1α, and increased ferroportin expression leads to iron reduction in myocytes by exportation of intracellular iron. […] Iron deficiency is a substantial factor in mitochondrial membrane potential and myocyte population reduction.

• #2 UPDATE Delayed Onset Muscle Soreness (DOMS) – Muscle Biomechanics, Pathophysiology and Therapeutic Approaches

  https://www.germanjournalsportsmedicine.com/archive/archive-2024/issue-5/update-delayed-onset-muscle-soreness-doms-muscle-biomechanics-pathophysiology-and-therapeutic-approaches/

  A protein degradation, autophagia and local inflammation reactions are elicited by the damage mechanism. […] The pathophysiology of DOMS underlines the decisive influence of mechanical stress as the primary elicitor of this injury entity. […] The central target of prevention of DOMS is to prevent or alleviate the onset of the initial damage, known as Exercise Induced Muscle Damage (EIMD).

• #2 Should You Stretch A Muscle Strain? — Physio Network

  https://www.physio-network.com/blog/stretch-muscle-strain/

  It is important to note that one single eccentric contraction, with enough rapid strain, can be enough to cause a mechanically-induced muscle tear, independent of other factors. Despite these purely mechanical instances, the large majority of muscle strains are multifactorial in nature. Identifying and addressing underlying risk factors is imperative if we are to successfully rehabilitate and prevent muscle strains effectively.

• #2 Diagnostics and classification of muscle injuries in sports – SEMS-journal

  https://sems-journal.ch/990

  The grade and size of direct muscle injuries depend on the intensity, the velocity and the state of contraction at the time of contact, and can occur at almost any localization of the muscle. […] In general, direct muscle injuries are of lesser degree than indirect muscle injuries, since there is no loss of continuity of the muscle fibers, and therefore the mean lay-off time is expected between 2-3 weeks. […] Longer time to recovery is found in indirect muscle injuries, greater deficit in range of motion, pain while walking 24-72 hours after the injury, time to first consultation 1 week with a delay of active rehabilitation, proximal tendon involvement, shorter distance to the ischial tuberosity and the antero-inferior iliac spine. […] Re-injuries most frequently occur early after return to sport, and at the same localization with a greater extent. […] There is no classification system for muscle injuries in literature that comprehends all major factors describing the severity and especially the estimated time-loss until return to sport.

• #3 Diagnostics and classification of muscle injuries in sports – SEMS-journal

  https://sems-journal.ch/990

  Muscle injuries occur in up to 40% of all professional football players per season and are responsible for up to one third of all musculoskeletal injuries recorded during international football tournaments and Summer Olympic Games. […] Most frequently, muscle injuries occur due to a sudden eccentric overload such as while sprinting, kicking, or due to an abrupt and forceful slippage, causing the indirect muscle injury. […] Indirect muscle injuries are mainly found in muscles that bridge two joints (such as the rectus femoris of the quadriceps muscle, the medial gastrocnemius muscle or the hamstring muscle group) containing mainly fast-twitch type 2 fibers, which have greater contraction velocity and greater capacity to change length, however less capacity to withstand tension. […] Ideally, a classification system permits to make a precise diagnosis and a prognosis for time-loss with the objective to allow to tailor an adequate treatment plan and finally to reduce the rate of reoccurrence injuries that have been described in up to 13% of the cases.

• #3 Hamstring Muscle Injuries – OrthoInfo – AAOS

  https://orthoinfo.aaos.org/en/diseases–conditions/hamstring-muscle-injuries/

  Like strains, hamstring tendon avulsions are also caused by large, sudden loads. […] Muscle tightness. Tight muscles are vulnerable to strain. Athletes should follow a year-round program of daily stretching exercises. […] Muscle imbalance. When one muscle group is much stronger than its opposing muscle group, the imbalance can lead to a strain. This frequently happens with the hamstring muscles. […] Hamstring strains occur more often in adolescents because bones and muscles do not grow at the same rate. During a growth spurt, a child’s bones may grow faster than the muscles. The growing bone pulls the muscle tight. A sudden jump, stretch, or impact can tear the muscle away from its connection to the bone. […] Treatment of hamstring strains depends on the type of injury you have, its severity, and your own needs and expectations.

• #3 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Skeletal muscle healing follows a constant order, with no major changes depending on the cause (contusion, stretch or laceration). […] Three phases were identified in this process: destruction, repair, and remodeling. The last two phases (repair and remodeling) overlap and are closely related. […] Phase 1: destruction – characterized by rupture and subsequent necrosis of myofibrils, by the formation of hematoma in the space formed between the ruptured muscle, and by the proliferation of inflammatory cells. […] Phase 2: repair and remodeling – consists of the phagocytosis of the necrotic tissue, the regeneration of myofibrils, and the concomitant production of connective scar tissue, as well as vascular neoformation and neural growth. […] Phase 3: remodeling – maturation period of regenerated myofibrils, contraction and reorganization of scar tissue, and recovery of muscle functional capacity.

• #3 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/

  Blood-derived fibrin and fibronectin intersperse to form granulation tissue, an initial frame and anchoring of the site for the recruited fibroblasts. […] More importantly, this new formed fabric provides the property of initial tension to resist the contractions applied against it. […] Approximately 10 days after the trauma, the maturation of the scar reaches a point in which it is no longer the most fragile site of the muscle injury. […] Although most skeletal muscle lesions heal without the formation of disabling fibrous scar tissue, fibroblast proliferation may be excessive, resulting in the formation of dense scar tissue within the muscle lesion. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

• #3 Overview of Sprains and Other Soft-Tissue Injuries – Injuries; Poisoning – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/injuries-poisoning/sprains-and-other-soft-tissue-injuries/overview-of-sprains-and-other-soft-tissue-injuries

  Serious complications of sprains, strains, and tendon injuries are unusual but may cause permanent limb dysfunction. […] Compartment syndrome threatens limb viability (possibly requiring amputation) and survival. […] Various ligament injuries, particularly 3rd-degree sprains, can lead to joint instability. Instability can be disabling and increases the risk of osteoarthritis. […] Injuries that result in joint instability predispose to repeated joint stresses that can damage joint cartilage and result in osteoarthritis. […] Many 3rd-degree sprains and tendon tears require surgical repair.

• #3 How to Prevent Muscle Strains • Stronger by Science

  https://www.strongerbyscience.com/how-to-prevent-muscle-strains/

  A muscle strain occurs when the strain energy the muscle is forced to absorb exceeds the strength of the tissue. […] A muscle strain is an indirect, structural injury. They’re often referred to as pulled or tweaked muscles. […] Strain energy is the key determinant of injury. […] Although the cause of acute muscle strains is often complex and multifactorial, most strains in strength training do share several common features. […] The precise location of a tear is a function of the distribution of stress throughout the tissue, but it’s most likely to happen near the junction between the muscle and tendon, because the transitional tissue is a bit weaker than either the muscle or tendon. […] The muscles most susceptible to strain injury include the hamstrings, quadriceps, hip adductors, hip flexors, abdominals, calves, and biceps.

• #3

  https://journals.lww.com/cjsportsmed/fulltext/2023/05000/mechanisms_of_hamstring_injury_in_professional.3.aspx

  Hamstring injury mechanisms typically involve hip flexion, knee extension, and trunk flexion. […] Single-tendon hamstring injuries (mostly BF) are typical in soccer and mainly occur due to high-speed movements involving high eccentric load of the hamstring muscles. […] Mixed-type injury mechanisms also occur, which include patterns from both sprinting-type and stretching-type injury mechanisms.

• #3 A Novel Muscle Atrophy Mechanism: Myocyte Degeneration Due to Intracellular Iron Deprivation

  https://www.mdpi.com/2073-4409/11/18/2853

  Myostatin, as an upstream regulator of atrogin1 and MuRF1, is a substantial target molecule for muscle atrophy caused by iron deprivation in myocytes. […] Our study demonstrated that muscle injury-induced hypoxic conditions lead to significant ferroportin expression, causing iron deficiency in myocytes. […] Intracellular iron deficiency induces decreased skeletal muscle mitochondrial quantity and function, resulting in impaired oxidative substrate metabolism and muscle loss. […] We also demonstrated for the first time that the nuclear receptor DAX1 is a regulator of myostatin expression in iron-deficient myocytes.

• #3

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8856841/

  Since myofibrils are fusiform and very long, there is an imminent risk that the necrosis initiated at the site of the lesion extends throughout the length of the fiber. However, there is a specific structure, called a contraction band, which is a condensation of the cytoskeletal material that acts as an „antifire system”. […] Once the destruction phase decreases, the present repair of muscle injury begins with two simultaneous and competitive processes: the regeneration of the myofibril route and the formation of the scar connective tissue. A balanced progression of these processes is a prerequisite for optimal recovery of contractile muscle function. […] Although myofibrils are generally considered nonlytic, the regenerative capacity of skeletal muscle is guaranteed by an intrinsic mechanism that restores the injured contractile tract. During embryonic development, an undifferentiated cell reserve pool called satellite cells is stored below the basal lamina of each myofibril. In response to the lesion, these cells first proliferate, then differentiate into myofibrils, and finally join each other to form multinucleated myobribules. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

• #4 Overview of Sprains and Other Soft-Tissue Injuries – Injuries; Poisoning – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/injuries-poisoning/sprains-and-other-soft-tissue-injuries/overview-of-sprains-and-other-soft-tissue-injuries

  Serious complications of sprains, strains, and tendon injuries are unusual but may cause permanent limb dysfunction. […] Compartment syndrome threatens limb viability (possibly requiring amputation) and survival. […] Various ligament injuries, particularly 3rd-degree sprains, can lead to joint instability. Instability can be disabling and increases the risk of osteoarthritis. […] Injuries that result in joint instability predispose to repeated joint stresses that can damage joint cartilage and result in osteoarthritis. […] Many 3rd-degree sprains and tendon tears require surgical repair.

• #4 SciELO Brazil – Muscle Injury: Pathophysiology, Diagnosis, and Treatment Muscle Injury: Pathophysiology, Diagnosis, and Treatment

  https://www.scielo.br/j/rbort/a/6DfKjzHq3RWrQxGGF57L4kv/?lang=en

  Approximately 10 days after the trauma, the maturation of the scar reaches a point in which it is no longer the most fragile site of the muscle injury. […] Although most skeletal muscle lesions heal without the formation of disabling fibrous scar tissue, fibroblast proliferation may be excessive, resulting in the formation of dense scar tissue within the muscle lesion. […] A vital process for the regeneration of the injured muscle is the area of vascularization. Restoration of vascular supply is the first sign of regeneration and is a prerequisite for subsequent morphological and functional recoveries.

Zobacz więcej