Hamstring strains are a very common injury that can sideline an athlete or put your typical fitness enthusiast out of commission for several weeks. In fact, hamstring strains make up 12-15% of all injuries in professional sports. In this article, I will discuss the pathophysiology of a hamstring strain, mechanism of injury and risk factors, and discuss rehabilitation techniques.
When a hamstring strain occurs, there is a rupture of the musculotendinous junction causing a tear. Once torn, a hematoma forms between the ruptured muscle fibers causing the formation of scar tissue. Initially, performing passive hip range of motion through its pain-free range is recommended. However, absolutely do not stretch an acute hamstring strain; any added stress can reverse healing and slow the recovery process. Lastly, as the recovery enters its final stages, the muscle fibers will begin to regenerate at the muscle-tendon junction. Advanced physical therapy is the quickest and safest way to complete this recovery.
Hamstring strains are separated into three different categories. A grade 1 strain is a mild injury that causes minor tearing of the musculotendinous unit and minor loss of strength. A grade 2 injury causes a moderate strain with a partial tear of the muscle-tendon until leading to a significant loss of strength that will result in functional limitations. A grade 3 hamstring strain is categorized as a complete rupture of the unit and is associated with severe functional disability.
The primary cause for a hamstring strain is a high-velocity eccentric contraction during body hip flexion and knee extension occurring simultaneously. Sprinting greatly mimics this body position and is the primary activity that leads to a hamstring strain. The major factors that can increase hamstring strain occurrences are a lack of flexibility, improper warm up, muscle imbalance between the quadriceps and hamstrings, and having a previous hamstring strain that was not properly rehabilitated. Those who have had a previous hamstring strain are at twice the risk of re-injury with 1/3 of hamstring injuries recurring in the first year.
When rehabilitating a hamstring strain, it is vital to avoid immobilization and start isometric contractions to maintain fiber alignment and facilitate myoblast regeneration. You can start isometric contractions on the same day of the injury, but avoid the temptation to stretch the injured hamstring until the muscle fibers have healed.
By day three, submaximal isotonics such as simple flexing and extending of the knee can limit scar formation without accidentally reinjuring muscle fibers. By days 10-14, you can start low-level eccentrics to prevent atrophy during fiber regeneration.
As the hamstring strain continues to heal, it’s vital to progress your exercise program with a variety of lengthened state eccentric exercises. Lengthened state eccentric exercises have been found to be most effective in strengthening the hamstring and effective in reducing the risk of reinjury.