Response to Ian Shrier

We agree with Ian Shrier that the finding of an effect of stretching on risk of muscle, ligament and tendon injuries should be interpreted with caution. That is why we wrote “The finding of an effect of stretching on muscle, ligament and tendon injury risk needs to be considered cautiously because muscle, ligament and tendon injury risk was a secondary outcome, and there was no evidence of an effect of stretching on the primary outcome of all-injury risk. If stretching had reduced the risk of muscle, ligament and tendon injuries without increasing the risk of other injuries, we would expect a reduction in all-injury risk.” Nonetheless, after a prolonged discussion of this issue we decided that the finding could not be totally dismissed. We believe that it was appropriate to report the observed effect on muscle, ligament and tendon injuries with an explicit acknowledgement of the uncertainty associated with this finding.

Regardless of whether one accepts the finding that stretching reduces risk of muscle, tendon and ligament injuries, the implications would appear to be the same. Even if the effect is real, it is quite small in absolute terms (even in this population, at quite a high risk of injury, only “one injury to muscle, ligament or tendon was prevented for every 20 people who stretched for 12 weeks”). For this reason the data from this study do not appear to provide support for the practice of stretching, at least in so far as the aim is to reduce injury risk. The stronger justification for stretching, though still a marginal one in our view, is provided by the clear evidence of a very small effect of stretching on soreness. For other outcomes, such as performance or range of motion our study did not provide any data.

It is not yet known whether stretching is best carried out before exercise, after exercise, or both before and after exercise. We were surprised, when planning this study, to learn that most Australian stretch before exercise but not after, and most Norwegians stretch after exercise but not before! It was for that reason we designed a trial in which participants stretched both before and after exercise. We do not agree with Ian Shrier’s suggestion to conduct an unplanned post-hoc comparison of the non-randomised subgroups that chose to stretch only before, only after, or both before and after exercise. Such an analysis would almost certainly be seriously confounded and would probably be uninterpretable; at any rate it hardly seems consistent with his disapproval of our much more disciplined pre-planned secondary comparison between randomised groups. The only truly satisfactory way to resolve the issue of whether it is better to stretch before or after exercise is to conduct a further randomised trial in which participants are randomised to those two conditions.

Conflict of Interest: None declared

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