2. Muscle injuries

3. Muscle injury is the most common musculoskeletal complaint in the athlete. Common muscle injuries include muscle strains, delayed muscle soreness, contusions, and cramps. Muscle injury results in 15%–50% of all injuries sustained in sports. More than 90% of these frequent injuries are contusions and strains, whereas laceration is considered the least frequent

4. The injury occurs when selected muscles restrict range of motion of the joint they cross and a significant amount of tension is placed on that muscle ■ Clinically, muscle injury (strain/contusion) is classified depending on the level of damage generated: mild when the loss of strength and movement is minimal or nonexistent, moderate with inability to contract severe for absolute loss of function.

5. PHYSICAL REHABILITATION OF THE INJURED ATHLETE

7. Mechanism of Injury ■ Although a concentric muscle contraction alone is insufficient to create muscle strain injury, the force per fiber is higher in the relatively few muscle fibers needed during eccentric muscular contraction. The combination of passive stretch of the muscle past its resting length, eccentric loads, and the subsequent concentric contraction is required to injure the muscle This overextension and tension development can then disrupt the myofibers near the myotendinous junction (26). ■ Cellular disruption results in the hydrolysis of structural proteins and inflammation that further damages the muscle tissue

8. Factors that contribute to muscle strain injury—inadequate flexibility, inadequate strength or endurance, dyssynergistic muscle contraction, insufficient warm-up, or inadequate rehabilitation from previous injury

9. The most frequent muscle strain injuries occur to muscles that cross two joints, muscles such as the gastrocnemius, hamstring complex, gracilis, and rectus femoris

10. Disruption of fibers occurs near the myotendinous junction, not necessarily at the junction itself, The disruption usually occurs a short distance from the tendon, ranging from 0.1 mm to several millimeters. The response to injury at the myotendinous junction is limited to the area of injury and is usually extremely focal in nature.

12. After injury the healing process sets up two competitive events, the regeneration of muscle fibers and the production of fibrous scar tissue (repair) During this process three phases are present: destruction repair (regeneration) remodeling.

14. SCIENTIFIC_FOUNDATIONS_AND_PRINCIPLES

16. Delayed Muscle Soreness ■ Delayed muscle soreness is defined as skeletal muscle pain 24–72 hours after unaccustomed physical activity. The pain lasts approximately 5–7 days and can range from mild soreness to severe discomfort. Loss of both muscle strength and joint range of motion, tenderness, and elevated muscle enzymes are also present.

17. Reduced range of motion and elevated levels of creatine kinase are common 1–2 days after the strenuous exercise; however, peak creatine kinase levels have not been shown to be correlated with the temporal aspects of pain or degree of tissue injury

18. Delayed muscle soreness occurs most commonly in fast type muscle fibers when performing eccentric activity and is related to both the intensity and duration of activity

19. No permanent muscle injury occurs, and complete recovery is seen within 14 days. The adaptation to the unaccustomed exercise (i.e., less soreness with successive bouts of the exercise) is rapid.

20. Delayed muscle soreness diminishes with repetition of exercise; Light activity and stretching preserve range of motion for reasons that remain unclear. There is still continued muscle tissue damage with repetitive exercise, but to a progressively lesser extent. Perceptual discomfort associated with this tissue damage, however, is greatly diminished.

21. Muscle Contusion Injury ■ Muscle contusions are common injuries in collision and contact sports. These soft tissue injuries are frequently caused by impact with a blunt, non penetrating object. In most cases, contusions involve the lower extremity muscle groups such as the quadriceps, gastrocnemius, or anterior muscles of the Leg.

22. The initial clinical presentation includes pain, swelling, loss of joint range of motion, and the possibility of a palpable muscle defect. This can be followed by persistent swelling and warmth, a firm mass, and continued loss of motion.

23. PHYSICAL REHABILITATION OF THE INJURED ATHLETE

24. Reparative Response ■ The process of muscle contusion healing is similar to the general process of muscle healing, involving a combina tion of the formation of scar tissue by fibroblasts and the regeneration of normal muscle by migrating myoblasts. There appears to be less scar formation from a contusion than with a muscle strain injury

25. RICE principle is usually the fi rst treatment option for the athlete immediately after the injury. Brief immobilization ( 5 days) leads to faster healing without further tissue damage, whereas prolonged immobilization results in muscle atrophy and delayed muscle activity. In addition, early mobilization results in increased tensile stiffness of contused muscle and more rapid resolution of the contusion injury

26. Muscle Cramps ■ Muscle cramps affect both athletes and non athletes. The gastrocnemius, hamstrings, and quadriceps muscles are most commonly involved, but cramping can involve nearly any muscle group. Cramps begin with the muscle in a shortened position.

27. The development of muscle cramps usually starts with a twitching of the muscle due to skeletal muscle fatigue (“cramp-prone state”), followed by spasmodic spontaneous contractions and pain.

28. Passive stretching is the most reliable immediate treatment to alleviate the cramped muscle group. Fluids and sodium replacement are still considered, but their use is controversial, and the effect is equivocal

29. Muscle Laceration ■ Muscle laceration is seen more often in trauma than sports. When a muscle is completely lacerated, 50% of its strength and 80% of its ability to shorten can be expected to be lost ■ In a murine model, immediate suturing of the fascia of the lacerated muscle has been shown to favor healing and to suppress the formation of deep scars, whereas with immobilization, the regeneration time of the injured muscle was longer and the scar was considerably larger.

30. When the remodeling phase is complete, the damaged tissue has often not achieved the same tensile strength as uninjured tissue. Luckily, the limitation in tensile strength does not typically affect function. The three phases of tissue healing overlap and represent a continuum of soft tissue healing.

31.  Treatment Reduced activity is key in the treatment of muscle strain injuries.  This helps control inflammation and prevents further tissue damage.  The RICE principle (rest, ice, compression, and elevation) should be implemented immediately after skeletal muscle injury.  Immobilization can diminish pain, reduce inflammation, and allow torn muscle ends to reaproximate.

32. PREVENTION Important factors for preventing muscle strains include maintaining flexibility and proper conditioning, which is achieved through stretching and strengthening, respectively.

33. the viscoelastic property of muscle is affected by warmth and can contribute greatly to changes in muscle length. Therefore, warm-up should facilitate stretching and thus prepare the muscle- tendon units for exercise

34. fatigue may also play a role in injury, so proper training and conditioning are important for prevention of injuries. Unfortunately, in our experience prevention is more helpful in those who have not had a previous injury. It appears that once injured, individuals remain at a higher risk for reinjury than their not previously injured cohort.

35. Immobilization and aging effects on muscle

36. Immobilization Immobilization results in large and rapid changes in size, strength, and functional capacity of skeletal muscle. Hespel et al. showed that 14 days of immobilization resulted in a ∼ 11% decrease in whole muscle size, accompanied by an 8% to 11% decrease in the area individual muscle fiber types As size and strength are closely coupled, it is logical to assume that decrements in muscle size produce falls in muscle strength. It has been shown that just 9 days of immobilization decreased isometric strength by 13%, while 14 days may decrease strength by 22%. Strength decreases following immobilization appear to be speed specific, as strength at slower angular velocities falls more than at faster velocities.

38. With aging, the cross-sectional area of muscle declines and the number of muscle fibers decreases by about 39% by age 80. Type I muscle fibers are not affected much by aging, but type II fibers demonstrate a reduction in cross-sectional area of 26% from age 20 to 80, Aging thus leads to Smaller muscle mass, a higher proportion of type I fibers, and less strength secondary to denervation of type II fibers.

39. Changes in skeletal muscle from aging seem to be secondary to the decline in demands on muscle and lack of physical activity, and thus can be minimized or even reversed with adequate training.

40. All of these changes translate into an increase in collagen and connective tissue content in relation to actin-myosin complexes and force-generating capacity. Greater possibility exists of muscle stiffness and a loss of flexibility with less strength and subsequent decrease in physical function.