Hamstring strains are one of the most common sporting injuries. Anyone involved in any type of running sport can attest to this. I’ve already seen multiple hamstring injuries at my local hockey club even though I’ve only being helping out for the past few weeks. According to the research hamstring injuries account for 6-29% of all sporting injuries (this value differs slightly depending on which paper you read) (Mendiguchia, 2011) (Woods, 2004). As you would expect there certainly is a wealth of information available on hamstring injuries, one quick search in PubMed (a research search engine) showed that ~2000 papers related to hamstring injuries have been published in the past 5 years alone. However, as I was perusing through some research I came across an interesting editorial piece published in the British Journal of Sports Medicine (BJSM) “Hamstring Strains: Are we heading in the right direction?” (Mendiguchia, 2011). This editorial piece shows that despite a wealth of information available about hamstring strains there has actually been noimprovement in hamstring injury and re-injury rates over the past 3 decades (Mendiguchia, 2011). So, despite everything we’ve learned over the past 30 years we are still seeing the same rates of hamstring injury as 1990. Why is this?
30 years is a long time, I wasn’t even born 30 years ago. The fact that there have been no improvements in reducing hamstring injury and re-injury rates is interesting, is something being overlooked? More on this later. First what typically happens when someone sustains a hamstring injury? Hopefully, that individual will begin some form of supervised rehabilitation program where they are progressing from stage to stage until they eventually meet specific return to play to play criteria and are allowed back onto the field. These programs are extremely thorough and designed according to the best evidence available, yet despite this we still see the same injury rates as 3 decades ago. Why? Could it be that individuals are not completing their rehabilitation correctly? (Faber, 2015) Or that athletes return to play before reaching the required criteria? (Menta 2016) Well the research suggests that both of these actually occur. Now to play devil’s advocate here it is known that there is a time lag of about 17 years from scientific discovery to implementation into health care (Morris, 2011). Which is why as health practitioners we are expected to keep up to date the current literature (many don’t). However, even at the elite sporting level with highly skilled practitioners (who we can expect to be reading the latest research) and dedicated athletes committed to their rehabilitation program, we still see high rates of re-injury for hamstring strains. In fact, most of the research is actually undertaken on elite athletes (Woods, 2004). So, with some liberties we can assume the lack of improvement is not due to the failure of implementation of current literature. So even in an idealistic situation where the current literature is being implemented and rehabilitation programs are being strictly adhered to, we are still seeing the same hamstring injury and re-injury rates as the past 3 decades. Once again why is this? Well in the article published in the BJSM by J. Mendiguchia (referred to here on as M and Co) (“Hamstring strain injuries: are we headed in the right direction?”) proposes that the reason for the lack of improvements over the past 3 decades is actually due to the current approach to research and the subsequent implemented rehabilitation programs (Mendiguchia, 2011).
M and Co go on to describe how the current approach to research is reductionist or unidirectional. In which researchers aim to find a direct link (or cause and effect) relationship between risk factors and injury rates (x causes y). For example, one such study evaluated hamstring tightness in pre-season athletes and then recorded the amount of hamstring strains the athletes received throughout the season (Bradley, 2007). This study showed that athletes with tighter hamstrings in pre-season were more likely to sustain a hamstring strain during the season (hamstring tightness (x) causes hamstring strain (y)) (Bradley, 2007). Then in theory, if we increase the athletes hamstring flexibility they will be much less likely to develop a strain. This research method has allowed researchers to identify numerous hamstring strain risk factors including: hamstring tightness, eccentric hamstring strength and even ankle sprains. Then researchers will specifically address these risk factors when designing up to date rehabilitation programs and return to play criteria. This happens in a similar fashion to a checklist, ensuring that the athlete has met all criteria reducing their risk of injury before returning back to play. Yet despite this (and yes, I hate to remind you again) we still have not seen a reduction in hamstring strain injury and re-injury rates in the past 3 decades. Clearly something is being overlooked.
Current Effect cause for Injury vs New conceptual model for injury. Image taken from (Mendiguchia, 2011)
M and Co propose that this unidirectional, cause and effect approach to research fails to address the complex multifactorial relationship of injuries (Mendiguchia, 2011). Going back to our previous paper where we identified that hamstring tightness is a predictor of hamstring strain. This paper looks at hamstring tightness in isolation. It does not assess whether the athlete has any of the other risk factors for hamstring strains (previous ankle injury, eccentric hamstring strength, quadricep to hamstring ratio). Further to this it does not address why the individual’s hamstrings are tight. Could it be that the athlete had an intense hamstring work out the day before testing and had tighter hamstrings that day? Or does the athlete may have weak hip extensors causing the hamstrings to be overworked leading to the tightness? Or does the athlete have a particular running style that predisposes their hamstrings to be overworked? This paper and many others often don’t address causative factors instead just focus on the issue (hamstring tightness). M and Co state that injuries are often not caused by independent risk factors acting in isolation, instead injuries are caused by the interaction and interplay of multiple risk factors (Mendiguchia, 2011).
M and Co propose that the reason we have not seen a reduction in hamstring injury rates is because these risk factors are not being assessed in conjunction with each other, instead in isolation, like a checklist (their interactions are not assessed) (Mendiguchia, 2011). Also, the way many of these tests are performed in an artificial environment and do not reflect how the injury would actually occur. For example, hamstring tightness is typically evaluated with the patient lying on their back, their entire straight leg is lifted off the table until the patient reports tightness. However, hamstring strains typically occur in terminal stance phase of gait where the muscle is under stretch but in a very different environment from the one tested clinically.
Clearly, there is a disconnect between clinical testing and real-world injury mechanisms and this may play a part in the previously stated lack of improvement. The clinical tests often times don’t correlate to the functional task or injury mechanism. This in itself though is difficult to test and or isolate. The reason researchers have to test in an artificial environment is largely due to the scientific method. For a research paper to be accepted it has to adhere to certain standards of reliability and validity. With increasing the complexity of testing parameters (more functional testing), you introduce greater variables that may have an effect on testing parameters. And if you have more variables that could have potentially had an effect on the research data, the harder it is do make a direct correlation between two variables (less reliable and valid), which is the purpose of research. Thus, typically testing occurs in an artificial environment. This is why Mand Co propose that the lack of improvement in hamstring strains is due to the wayin which research is conducted as opposed to what research is being conducted (Mendiguchia, 2011). The current research methodology has worked wonders over the past several decades, however as discussed it is not perfect. Perhaps more research into the way we conduct research is needed?
The lack of improvement over the past 3 decades in hamstring injury rates is quite troubling, though the exact reason is still up for clinical debate. M and Co proposes one possible cause, however until research is done into this we won’t know for sure. Regardless if you have hamstring issues, ensure that you are seeing a practitioner who takes you through a thorough rehabilitation program that is unique to you. And if you have suffered multiple (or recurrent) hamstring injuries but you keep performing the same rehabilitation program, something may be getting missed. And perhaps as M and Co suggest you may require a more thorough integrated assessment to get to the cause of your problem.
Thanks for reading.
Mendiguchia, J., Alentorn-Geli, E., & Brughelli, M. (2011). Hamstring strain injuries: are we heading in the right direction?. British journal of sports medicine, bjsports81695. Available from: http://bjsm.bmj.com/content/46/2/81.long
Woods, C., Hawkins, R. D., Maltby, S., Hulse, M., Thomas, A., & Hodson, A. (2004). The Football Association Medical Research Programme: an audit of injuries in professional football—analysis of hamstring injuries. British journal of sports medicine, 38(1), 36-41. Available from: http://bjsm.bmj.com/content/38/1/36
Morris, Z. S., Wooding, S., & Grant, J. (2011). The answer is 17 years, what is the question: understanding time lags in translational research. Journal of the Royal Society of Medicine, 104(12), 510-520. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3241518/
Menta, R., & D’Angelo, K. (2016). Challenges surrounding return-to-play (RTP) for the sports clinician: a case highlighting the need for a thorough three-step RTP model. The Journal of the Canadian Chiropractic Association, 60(4), 311. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5178014/
Faber, M., Andersen, M. H., Sevel, C., Thorborg, K., Bandholm, T., & Rathleff, M. (2015). The majority are not performing home-exercises correctly two weeks after their initial instruction—an assessor-blinded study. PeerJ, 3, e1102. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4517955/
Bradley, P. S., & Portas, M. D. (2007). The relationship between preseason range of motion and muscle strain injury in elite soccer players. Journal of Strength and Conditioning Research, 21(4), 1155. Available from: https://www.ncbi.nlm.nih.gov/pubmed/18076233