William Garrett

Acute hamstring muscle strains occurring in ten college athletes were evaluated using computed tomography to identify the location and characteristics of these common injuries. Acute muscle strains appeared as areas of hypodensity within the muscle 1-2 d following injury. This suggests that inflammation and edema are the major component of injury, not bleeding as commonly assumed. Injuries were seen most commonly in the proximal and lateral portions of the hamstring muscle group, particularly in the biceps femoris.

Most muscle stretching studies have focused on defining the biomechanical properties of isolated elements of the muscle-tendon unit or on comparing different stretching techniques. We developed an experimental model that was designed to evaluate clinically relevant biomechanical stretching properties in an entire muscle-tendon unit. Our objectives were to characterize the viscoelastic behavior of the muscle-tendon unit and to consider the clinical applications of these viscoelastic properties. Rabbit extensor digitorum longus and tibialis anterior muscle-tendon units were evaluated using methods designed to simulate widely used stretching techniques. Additionally, the effects of varying stretch rates and of reflex influences were evaluated. We found that muscle-tendon units respond viscoelastically to tensile loads. Reflex activity did not influence the biomechanical characteristics of the muscle-tendon unit in this model. Experimental techniques simulating cyclic stretching and static stretching resulted in sustained muscle-tendon unit elongations, suggesting that greater flexibility can result if these techniques are used in the clinical setting. With repetitive stretching, we found that after four stretches there was little alteration of the muscle-tendon unit, implying that a minimum number of stretches will lead to most of the elongation in repetitive stretching. Also, greater peak tensions and greater energy absorptions occurred at faster stretch rates, suggesting that the risk of injury in a stretching regimen may be related to the stretch rate, and not to the actual technique. All of these clinically important considerations can be related to the viscoelastic characteristics of the muscle-tendon unit.

Musculotendinous injuries are responsible for a significant proportion of injuries incurred by athletes. Many of these injuries are preventable. Importantly, musculotendinous injuries have a high incidence of recurrence. Thus, muscle injury prevention is advocated by coaches and trainers. Yet, most of the recommendations for muscle injury prevention are attempted by athletes and taught by coaches without supporting scientific evidence. This paper reviews the mechanics of muscular injury, associated and predisposing factors, and methods of prevention with a review of the supporting research and rationale for these methods with an emphasis on warm-up, stretching and strengthening. Muscles that are capable of producing a greater force, a faster contraction speed and subjected to a greater stretch are more likely to become injured. Many factors have been associated with muscular injury. From current research, some conclusions and recommendations for muscle injury prevention can be made. Overall and muscular conditioning and nutrition are important. Proper training and balanced strengthening are key factors in prevention of musculotendinous injuries as well. Warm-up and stretching are essential to preventing muscle injuries by increasing the elasticity of muscles and smoothing muscular contractions. Improper or excessive stretching and warming up can, however, predispose to muscle injury. Much research is still needed in this important aspect of sports medicine.

This study investigates the biomechanical failure properties of five architecturally different skeletal muscles and examines the role muscle structure plays in the passive extension characteristics of musculotendinous units. The muscles used in this study fall into four morphologic categories: fusiform, unipennate, bipennate, and multipennate. Each muscle was pulled to failure at three different rates of strain (1, 10, and 100 cm/min). Specimens of fusiform, unipennate, and bipennate muscles were pulled from their proximal as well as distal attachments. The relationship of elongation to failure of the entire musculotendinous unit to resting muscle fiber length was examined to determine the effect of angle of pennation and fiber length on the failure properties. Our results demonstrate that all four muscle types tested show injury and rupture at the musculotendinous junction whether pulled from proximal or distal attachment, regardless of muscle structure and rate of strain. There was a statistically significant difference (P less than 0.005) in the degree of elongation to failure relative to resting muscle fiber length, with a tendency to greater elongation relative to fiber length for muscles with more pennate structure (tibialis anterior, 72.7% +/- 1.0%; extensor digitorum longus, 113.1% +/- 3.5%; rectus femoris, 225.5% +/- 3.7% elongation in percent resting fiber length).