Abstract & Commentary
Synopsis: This study concludes that delayed eccentric exercise is an important component of a rehabilitation protocol designed to avoid recurrent hamstring strains. Low eccentric-concentric hamstrings to quadriceps strength ratios are indicative of a predisposition toward hamstring reinjury.
Source: Croisier JL, et al. Am J Sports Med. 2002;30(2): 199-203.
Although recurrent hamstring strains are a major problem in sports medicine, we have seen few advances in recent years in returning athletes to injury-free sports participation. Hamstring strains are among the most common athlete injuries and the incidence of recurrence is high. How common are they? A multi-year study in Norway and Iceland found that hamstring strains were the most common injury in male soccer (13-17% of all injuries). Ankle sprains, knee sprains, and groin strains were all less common. How problematic are these injuries? One only need to follow the story of Ken Griffey, Jr., in major league baseball, which turned the national spotlight on recurrent hamstring injury and the devastating effects of this injury on playing time. Recurrent hamstring strains are an important sports medicine dilemma.
Using isokinetic testing, Croisier and colleagues studied 26 male athletes including soccer (14), track and field (7), and martial arts (5) athletes with a history of recurrent hamstring muscle strains. Those athletes with low hamstring-to-quadriceps strength ratios were treated with 10-30 visits, 3 times a week, with a customized rehabilitation protocol that focused on isokinetic training to address their strength deficit. The isokinetic training used eccentric/concentric modes or both, and hamstring to quadriceps strength ratios were tested at 30°/second eccentric mode and 240°/second concentric mode. Maximal concentric training was performed from the beginning of the training protocol; eccentric training was progressive in the initial phase and built up to maximal effort contractions. Eccentric training was performed to full extension. Following this program, none of the athletes developed hamstring strains or symptoms in the ensuing 12 months of full sports participation.
Croisier et al’s first hypothesis was that delayed eccentric exercise is an important component of a rehabilitation protocol designed to avoid recurrent hamstring strains. The second hypothesis was that one could use hamstring to quadriceps strength ratios to predict hamstring strain recurrence. Croisier et al presented some evidence supporting the first, but not the second hypothesis.
Comment by Timothy E. Hewett, PhD
Croisier et al suggest that muscle imbalances underlie recurrent hamstring strains. They do not hypothesize whether the imbalances exist prior to injury and predispose the athlete to the initial injury, or the suggested imbalances result from injury. The review of the literature was very sparse due to the dearth of literature in this area of study. Croisier et al concluded from the literature that recurrent strains result from inadequate rehabilitation following the injury.
Croisier et al did not present the rehabilitation protocol in sufficient detail to allow a physical therapist’s clinical implementation. They used an individually customized rehabilitation protocol, which is a problem with the study. It is difficult to draw conclusions from testing a rehabilitation protocol that is not consistent across all study subjects. Another problem is that they use their findings to draw conclusions about the ability of the hamstring to quadriceps strength ratios to predict hamstring strain recurrence. They did not adequately test this hypothesis.
Although there are several problems with the study design and the conclusions drawn from this study, it is a good starting point for us to more critically examine this important problem in sports medicine. I would wonder why they used such slow training speeds? Sports activities occur at much higher speeds which can exceed 500°/second. Is the next step to screen athletes for low hamstring to quadriceps ratios preseason and train those with deficits?
There are new data from Norway that agree with the findings presented in this paper. At the most recent meeting of the American College of Sports Medicine,1 Raold Bahr presented data that demonstrated that eccentric hamstring training using a modified Russian/Nordic hamstrings exercise significantly reduced the occurrence of hamstring strains in the Norwegian National Men’s Soccer team over several seasons. In summary, it appears that eccentric hamstring training may decrease the recurrence of hamstring muscle strains. However, the jury is still out on whether hamstring to quadriceps strength ratios can be used to predict those who will develop problems.
Dr. Hewett, Director and Assistant Professor, The Sports Medicine Biodynamics Center, University of Cincinnati College of Medicine, Cincinnati, OH, is Associate Editor of Sports Medicine Reports.
Reference
1. Bahr R. The 49th Annual Meeting of The American College of Sports Medicine. May 28-June 1, 2002, St. Louis, Missouri.
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