Hamstring injuries are common in athletes who run sprints. Because of this, a lot of research has been done to attempt to establish why this is. Theories abound including flexibility, running technique, hamstring strength, and eccentric hamstring strength all being the major theories. There has not been a lot of research effectively establishing a link between flexibility and hamstring injuries. Running technique is difficult to quantify and agree on an ideal model, so this one is also difficult. So the majority of the research looks at strength.
Zvijac et al, in the August issue of the American Journal of Sports Medicine, look at the ration of hamstrings-to-quadriceps strength measured in the National Football League players who attend the combine and injuries suffered during the season. The authors followed 960 players. At the NFL combine, the athletes were tested on a Cybex dynamometer to establish their isokinetic strength at 3 reps and 15 reps for both the quadriceps and the hamstrings.
Of the 960 players, 21% suffered a hamstring injury during the season. Defensive backs, followed by wide receivers, followed by running backs suffered the highest prevalence of injuries and accounted for 67% of the hamstring injuries.
When looking at the differences between the injured leg and the uninjured leg, the authors did not find any differences between the two. For example, the injured leg had a hamstring-to-quadriceps ration of .66, the uninjured side had a ratio of 0.67. In addition, the hamstring-to-quadriceps ratios are identical for the injured players and the uninjured players. The authors concluded that the isokinetic strength data that was gathered at the combine is not useful in predicting hamstring injuries suffered during the season.
Now, one big flaw with this study is that an athlete’s hamstring strength in February may not be their hamstring strength in September through January when the injuries are actually occurring (keep in mind, this study looked at in-season injuries). This strength level can increase, decrease, remain the same, or fluctuate constantly. Test results four months before the season do not allow us to establish a relationship between the two variables.
Another interesting thought that the authors bring up is that the strength testing looks at concentric strength. Their point (and I agree) is that concentric strength may not be what is important when it comes to these injuries. Many of these injuries occur as the lower leg is uncoupling and being driven down to the ground, i.e. during a strong eccentric contraction of the hamstrings. It’s very possible that eccentric strength measures are going to be more important, and more predictive, or hamstring injuries. Just by looking at what is going on during sprinting, it would not hurt to work on strengthening the hamstrings while they are lengthened (i.e. Romanian deadlifts, good mornings, back raises, that sort of thing).
Zvijac, J.E., Toriscelli, T.A., Merrick, S., and Kiebzak, G.M. (2013). Isokinetic concentric quadriceps and hamstring strength variables from the NFL scouting combine are not predictive of hamstring injury in first-year professional football players. American Journal of Sports Medicine, 41: 1511-1518.