The Long and Short of Hamstring Muscle Injury and RecoveryAnyone who has injured the hamstring muscle is more likely to injure it again compared to others without injury. Athletes have the highest number of hamstring injuries. Soccer and track and field athletes miss more playing time because of hamstring strains than other athletes. These sports involve sprinting and sudden bursts of speed.
Researchers in Australia set out to study the link between damage to the muscle fibers and actual muscle tear in hamstring injuries. Do tiny tears in the muscles lead to a muscle strain with continued use of the muscle? The hope is to find ways of preventing such injuries.
Twenty-seven athletes were included in this study. Two groups were formed: one group without a previous history of hamstring injury, and a second group with an old hamstring injury on one side only. Some of the previously injured athletes had re-injured the same side more than once.
Each athlete was tested for hamstring strength. The angle at which the muscle was strongest in flexion and extension was recorded. For the injured athletes, the injured leg was compared to the uninjured leg. Researchers found that the previously injured muscles reached their peak sooner than uninjured muscles. This means the injured muscles worked best at a shorter length than uninjured muscles.
Strength differences between the hamstrings and quadriceps muscles didn't predict hamstring strain. In this study, type of sport didn't seem to make a difference, either. It all boiled down to the optimum length of the muscle. After injury, this length is shorter. Since muscles with shorter optimum angles are at greater risk of injury, repeat strains and tears are common.
The authors explain that, when a muscle gets stretched beyond its optimum length, small tears are likely. When the athlete uses the muscle to slow down or brake motion it's called an eccentric contraction. Repeated eccentric contractions cause more damage, and the size of the tear gets larger.
The authors suggest including eccentric exercise during rehab as soon as the athlete is pain-free after the injury. This will shift the optimum angle from shorter to longer, so injury is less likely.
Camilla L. Brockett, et al. Predicting Hamstring Strain Injury in Elite Athletes. In Medicine & Science in Sports & Medicine. March 2004. Vol. 36. No. 3. Pp. 379-387.
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