Hamstring Strains

So I thought I'd kick off my injury rehab reviews by looking at hamstring strains. With my work at Crystal Palace Football Club and in my Crossfit gym, I see a lot of these. In British football, hamstring injuries make up 12% of all injuries, with an average of 5 per club per season, resulting in 15 matches and 90 days missed (Hawkins et al, 2001). However, hamstring strains aren't just the reserve of football players - any activity involving sprinting is susceptible, and that includes Crossfit... 

The majority of hamstring injuries occur in the biceps femoris muscle, which is probably due to it's duel purpose of flexing the knee and extending the hip. Hamstring injuries usually occur when performing a maximal sprint, due to the fact that when maximally sprinting, the hamstrings are working eccentrically to decelerate the lower leg in the terminal swing phase, and then rapidly shortening concentrically to actively extend the hip. Heiderscheit (2005) identified the point at the end of the terminal phase, when the muscle is maximally activated and approaching peak length, as the most vulnerable to injury. 

According to Brunkner and Kahn, in their excellent Sports Medicine textbook, predisposing factors for hamstring strain can be divided into intrinsic and extrinsic factors. Intrinsic factors: (1) Increasing age, (2) Previous injury, (3) Poor flexibility, and (4) weak hamstrings. Extrinsic factors: (1) inadequate warm-ip, and (2) fatigue. Immediately we can see flexibility and muscle strength jump out at us straight away as two factors that we can have direct influence on through training and stretching. So, what does the literature say? 

Stretching

A survey conducted by Dadebo et al (2004) on professional football teams in the UK found that significantly more hamstring strains occured in those teams that did not stretch regularly, or that did not stretch adequately (holding stretches for longer than 20 seconds). Hartig et al (1999) also investigated the role of stretching in preventing hamstring strains: the authors split a group of soldiers into a control group following the usual military fitness regime, and an experimental group which had an additional stretching component. The intervention lasted 13 weeks. The stretching component involved 5 sets of 30 second stretches to both legs, daily. The study reported that, as expected, ROM increased for the stretching group, but, more importantly, there was a significantly lower incidence of hamstring strain in the stretching group compared to the control group (16.7% vs. 29.1%). 

In the acute phase of a hamstring strain, pain free ROM should be achieved as soon as possible. Malliarapolous et al (2004) studied the role of stretching in the rehabilitation of hamstring injuries in an eighty athlete cohort. The injured athletes were randomly assigned to the minimum stretching group (1 session a day), or the maximum stretching group (4 sessions a day). Each session consisted of a 30 second static hamstring stretch, repeated 4 times (therefore a total of 16 30 sec stretches on each leg for the intensive stretching group!). The results were again positive: the intensive stretching group had a significantly shorter time to regaining 'normal' ROM, and a significantly shorter period of time before returning to sport. 

These results have shown us that hamstring stretches are not only important for the rehabilitation of injuries, but also for avoiding hamstring injuries in the first place. But, if you're anything like me, you probably are interested in whether there are any strengthening exercises which can be employed as well. We don't just want to treat the problem - we want to cure it! 

Strengthening

In view of the probable mechanism of hamstring injuries (as previously discussed), it is likely that eccentric strength is particularly important in recovery and prevention of hamstring strains. Indeed, eccentric training has been shown to shift the point of peak torque development to a more lengthened position (Brocket, 2001), potentially protecting the muscle. A study by Askling et al (2003) examined the effects of pre-season eccentric strength training in Swedish elite soccer players. Thirty players were randomly placed into either a control group or an experimental group. Both groups continued with their usual training schedules, but the experimental group were given a supplemental programme of 16 hamstring eccentric strengthening sessions over a ten week period. 

These involved exercises such as Nordic Hamstring Exercises: http://www.youtube.com/watch?v=lH5Qwq3vdeA ... 

Interestingly, maximum running speed increased in the experimental group, compared to the control group. More importantly for this discussion, 10 out 0f 15 in the control group reported hamstring strains compared with only 3 of the 15 in the strengthening group. Clearly, a larger sample is needed before we can really state conclusively that eccentric strengthening is the way forward, but these results are clearly very impressive.

Strength imbalances between quadriceps muscle and hamstring muscles have also been implicated in the occurrence of hamstring strain. Brunkner and Kahn (2007) suggest that hamstring strength should be between 60% and 70% of maximal quadriceps strength. A study by Grouser et al (2002) assessed strength imbalances in 28 athletes with a history of 3 or more previous hamstring strains. After testing, 19 of these athletes were found to have significant quad-hamstring strength imbalance, and were given individualised strength programmes to correct these. After between 10 to 30 sessions (depending on the subject) 18 of the 19 had corrected their imbalance, and were allowed to return to sport. At a 12 month follow-up, none had sustained a clinically diagnosed hamstring strain. These results are tempered somewhat by the lack of the control group, but still provide a strong indication for the importance of balanced strength exercises.  Correct application of strengtheing exercises is, as always, vitally important. For example, in squats, encouraging athletes to 'sit-back-and-down', to feel the weight on their heels, and not allow their knees over their toes, we are encouraging them to engage this powerful posterior chain, of which the hamstrings make up an integral part. Otherwise athletes, and you see this in globo-gyms every single day, will sit to far forward in their squat, clean, etc, relying on their quadriceps for their strength and power. 

So there you have it. I believe the take home message for us is to encourage our clients and athletes to stretch, stretch, stretch, as well as to provide them with a well balanced strengthening exercise. Hamstring injuries can be frustrating due to their penchant for re-occurrence, so a full rehabilitation programme is always necessary to ensure that athlete is cured, and we're not just papering over the cracks until their next injury. 

Please contact me with your thoughts and views on this article either in the comments section, or on twitter: @declanhalpin ... Thanks!