One of the most important muscle groups in running is the hamstring. They are active at various stages in the gait cycle, work in both knee flexion and hip extension.
Tendon lesions are a major problem in sports. They are difficult to treat as treatment may take months. Tendon injury is common due to low metabolism, blood and nutrient supply. Tendons respond to mechanical stresses by adapting its metabolism, structural and mechanical properties.
Eccentric contraction occurs when the muscle tendon unit lengthens while a load or stress is applied producing the so called negative work. More force can be generated on tendon using eccentric contraction than in concentric or isometric contractions.
Eccentric exercises have proved to be successful in the treatment of tendinopathy, especially in Achilles and patellar tendons. Although the site of the lesion affects its outcome. It can be done with as much forces as tolerated without increasing pain. It enhances collagen production and alignment, blood flow and activates mechanoreceptors leading to increase muscle tendon unit thus improve ROM.
Eccentric exercises are based on 3 principles:
1-Length: It increases the resting length of muscle tendon unit which decreases strain occurring during joint movement.
2-Load: Increasing load on tendon increases tensile strength of the tendon.
3-Speed: increasing the speed will increase forces on the tendon.
Example: Achilles tendon program in which the patient stands on a step with hind foot off the edge then the patient lowers his heel downward both bilateral and on one leg.
Another example is the squats for patellar tendon on the ground and on a wedge on both legs or on single leg with and without knee flexion.