Active Voice: Does Acute Static Stretch Compromise Muscle Force?
By Anthony D. Kay, Ph.D.

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

Anthony D. Kay, Ph.D., is a senior lecturer in the Department of Sport, Exercise & Life Sciences at The University of Northampton in the U.K. His research focus includes examining musculotendinous mechanics, neuromuscular activity and force production. See the Jan. 2012 issue of ACSM's Medicine & Science in Sports & Exercise^® (MSSE) for a related research review he co-authored, titled “The Effect of Acute Static Stretch on Maximal Muscle Performance: A Systematic Review.”

Static stretching is a common physical activity conducted by athletic, recreational and clinical populations, employed primarily for the short-term benefits of increased flexibility and decreased muscle tension. It often induces feelings of exercise readiness and is thought to reduce the risk of muscle strain injury. However, over the past decade, a growing body of research has reported that muscular force can be compromised after acute stretching, which may negatively influence exercise performance. Position statements and exercise prescription guidelines from governing bodies including ACSM have continued to reflect this interpretation. However, before changing exercise recommendations, I believe it is our role as researchers to objectively, critically and systematically evaluate the literature, and to ask: do we really know whether stretching is or is not detrimental to muscular performance, and should we recommend or oppose its use?

As an active researcher in this area, I have read numerous articles that have reported significant losses in muscular force following acute static stretch. As such, the previous question appears to have been readily answered: stretching does appear to reduce muscle performance. So why the debate? Many articles have also reported no significant reductions in force. So we must ask the question: why are there equivocal findings reported? Does the duration of stretch influence reductions in force, and is it dependent on the individual, the muscle group stretched, the contraction mode or activity performed? Finding answers to these questions will allow us to give specific, evidence-based exercise prescription, which ultimately should be one of our primary aims.

Our recent systematic review on this topic in MSSE addressed several of these questions. After examining the data from more than 100 articles, we found a clear dose-response effect where the longer the total stretch duration, the greater the likelihood and magnitude of force losses regardless of contraction mode, muscle group or the activity performed. This is unsurprising, as dose-response relationships are common in many forms of exercise. However, the most relevant finding was that no significant or meaningful reductions were reported when the total duration of stretch was less than 30 seconds. Furthermore, the chance and magnitude of any effect with stretching lasting 30-45 seconds was small. Given that current practice in both normal and athletic populations is to stretch a muscle for about 15-20 seconds, this much publicized and controversial issue appears to have minimal, if any, practical relevance in the applied setting.

So what stance should governing bodies adopt, and what should our physical activity prescription be for stretching protocols? I believe it should be evidence-based. Short-duration stretching has not been shown to compromise muscle performance. Nonetheless, there is also little evidence that it has a beneficial influence, so why do we continue to advocate the use of pre-exercise stretching? The rationale for its use is clearly not muscular performance enhancement but injury prevention and/or perception of exercise readiness. The injury prevention contention is not without controversy itself; a review by McHugh & Cosgrave in 2010 concluded that stretching does not reduce the risk of chronic injury but can reduce acute muscle strain injury risk, and although the authors suggest the need for further research to clarify this point, it is clear that acute pre-exercise static stretching can be safely recommended.