Lately I have been seeing more and more hamstring strains as football season is underway. This brought me back to some of my old literature reviews from residency and my own personal research. Interestingly enough, many of the hamstring studies are poorly designed and have conflicting evidence. However, this review did a nice job breaking down some of the strengths and flaws of these studies. Additionally, the authors gave their opinions on some of the findings which I found especially useful. Below are some of the highlights....
- "In humans, MRI has shown evidence of scar tissue for up to 1 year after an athlete’s return to sport. The presence of scar tissue can alter muscle transmission pathway, decrease tendon/aponeurosis complex compliance, and consequently lead to a modification of deformation patterns in the muscle tissue adjacent to the fibrous scar."
- "However, the evaluation methods used to measure hamstring flexibility have been criticized for their static approach and inability to differentiate from lumbopelvic flexibility, which in turn has not been shown to be related to injury rates.
- "During running, the psoas of the contralateral leg had a greater influence on hamstring length than the hamstring itself."
- "The fact that most studies assess isokinetic strength during single joint movements may be one of the reasons for the current controversy since the hamstrings’ moment arms at the hip are nearly twice the length of those at the knee during the end of swing phase running."
- "However, a recent Cochrane Systematic Review conducted by Goldman and Jones has concluded that there is insufficient evidence to state that the protocols of eccentric training have the capacity to reduce hamstring injuries."
- "We believe that one major limitation may be the generalized use of the Nordic hamstring exercise, which works the knee flexors eccentrically but with the hip in a fixed position. During any movement, such as the swing phase of a sprint, the hip is not fixed but instead moves and works in coordination with the rest of the segments of the body."
- "There are many hypotheses that associate hamstring injuries with lumbopelvic stability."
Architecture of Hamstring Muscle:
- "It's been reported that hamstring injuries related to sprint actions affected mainly the proximal part of the biceps femoris, whereas overstretching injuries mainly involved the free proximal portion of the semimembranosus muscle."
- "It is well accepted that the prevalence of biceps femoris injury is much higher than the medial hamstrings."
- "Neural tension has not been shown to be a risk factor24 but it may indirectly have an affect through decreased ROM."