A Question

When I was sixteen I took Hapkido every day for two weeks with my brothers. It was a two week promotional offer which met our fiduciary capacity at the time. I still remember most of what I learned in those two weeks. My brothers and I were especially enthralled with a leg stretching machine they had at the dojo. We combined our resources and bought one later that year. Hundreds of hours later we were all limber as gymnasts. Limber that is in only one position, the position of the stretch machine, sitting with the legs abduction in a V.

Our training continued under the watchful eye of gravity and our video camera. After surviving flips off roofs and staged car vs. person collisions I managed to hurt myself. I jumped in the air and landed in the splits with more gusto and less stretching than usual. A sharp pain immediately arose below my gluteal fold. The orthopedic surgeon said I strained my hamstring. Having had a hamstring sprain I am now at higher risk of having another one.

Hamstring strains are the most prevalent soft tissue injury in sports and recreational activities that involve sprinting jumping and kicking¹. A muscle strain is defined muscle fiber damage resulting from  excessive stretch which disrupts the integrity of the vascular and connective tissue.  These injuries results in a loss of strength and performance, take up to a year to heal and have recurrence rates as high as 31%². Is there anything that can be done to prevent these injuries? More specifically, could eccentric strengthening exercise prevent both first-time and recurrent hamstring muscle strains?

Some Data

This topic was addressed by a systematic review of the literature published in 2008 in the North American Journal of Sports Physical Therapy and authored by OsitaHibbert et al. The review was updated in 2011 by Daniel Lorenz and Michael Reiman and published in the same journal.

An eccentric muscle contraction is one in which the muscle lengthens while contracting and a concentric is one in which the muscle shortens while contracting. While picking up a glass from the table the biceps produces a concentric contraction and an eccentric contraction while putting it down again.

The authors of the 2008 review found seven relevant articles three of which were randomized controlled trials and four were case series. All studied athletes most of which were soccer, rugby or track.

Of the randomized controlled trials one reported a reduction in hamstring strains in the eccentric group and two did not. Of the latter, one was plagued by poor adherence to the eccentric training program because of the intense muscle soreness it produced and the other used a very low-load eccentric intervention called leg swinging.

All the case series they reviewed reported a reduction in hamstring strain. These studies typically involved 8-12 soccer players with a history of hamstring strains doing eccentric training and subsequently not having a strain that year.  One of these cohort studies actually had about 200 subjects but the rest were not too impressive if you ask me.

My Interpretation

What is the proposed mechanism of action? Eccentric training results in a shift in the length-tension curve of muscle such that it is stronger at longer lengths. Muscle strain occurs when the stretch on a muscle exceeds its capacity. Thus being stronger at long length (when a muscle is stretched) sounds like a pretty logical way to prevent muscle strains.

What’s my verdict? The safe answer of course is that there is currently insufficient high quality evidence upon which to base a clinical decision. But that’s no fun now is it? I personally think eccentric hamstring training could prevent hamstring strain under the following conditions.

1) It is done with sufficient intensity and duration of training to produce an adaptation.

2) It is done intensely in the off-season to create an adaptation to the exercise that results in less soreness when it is done during the in-season. This is primarily so that people will stick to the program.

3) It is done at longer muscle lengths so the adaptations are more specific to the location where strains occur.

The Nordic Hamstring Exercise  is one of the more popular options. In this exercise you anchor your feet then slowly lower yourself down. My complaint with this exercise is that it is way too hard for most folks and it trains the hamstrings in a shortened position. I prefer the deadlift by Lorenz et al 2011.

References

1. Brooks JH, Fuller CW, Kemp SP, et al. Incidence, risk, and

prevention of hamstring muscle injuries in professional

rugby union. Am J Sports Med. 2006; 34:1297-1306.

1. Petersen J, Holmich P. Evidence based prevention of

hamstring injuries in sport. Br J Sports Med. 2005;

39:319-323.