Two recently published meta-analyses on the effects of pre-exercise stretching have received media attention.[1,2] In general, these studies arrived at the same conclusions as previous reviews: pre-exercise stretching reduces tests of performance (e.g. strength, power). This effect is minimal with stretches of very short durations and increases the longer the stretch is held. Although I have promoted similar conclusions in the past, clinicians should understand when it is appropriate to generalize these results to their patients and athletes, and when it is not.
First, the results refer to pre-exercise stretching. Stretching regularly over weeks to months increases tests of performance. The current results should not be applied to yoga or other forms of regular stretching.
Second, the studies measured tests of performance, not performance. Stretching before karate may allow one to kick higher. If stretching allows an athlete to hit the opponent in the head where this would not be possible without stretching, then stretching improves performance because hitting the opponent with a decreased force is better than not hitting the opponent at all!
Third, the original studies were conducted in healthy individuals. The effects of stretching in injured patients remain to be determined. Although stretching weakens healthy muscle, stretching also acts as an analgesic. Because pain from injured tissue causes muscle inhibition, reducing pain through stretching may or may not increase strength in this context.
Fourth, with regards to injury risk (not covered by these meta-analyses), other reviews have suggested that pre-exercise stretching does not reduce overall injury risk. Some authors have suggested pre-exercise stretching may reduce tendon injuries. However, if tendon injuries are reduced but total injuries remain the same, there must be an increase in other types of injuries (e.g. increased falls through decreased proprioception). In addition, similar to performance tests, some evidence suggests regular stretching might be beneficial even though pre-exercise stretching is not.
Fifth, research on the effect of stretching in injury rehabilitation is scarce. When stretching was compared to strengthening for rehabilitation, the strengthening group does much better.[8,9] To my knowledge, the potential benefit of adding stretching to strengthening in rehabilitation has not been evaluated.
Finally, different authors define the recently introduced term “dynamic stretching” differently. Generally, it refers to slow movements through a normal range of motion. Such activity does not increase range of motion [10,11] and should be considered as a method to increase muscle metabolic activity and temperature rather than a “stretch” per se. Therefore, the comparison group for such studies should be other forms of muscle activity and not types of stretching.
In summary, I agree with the authors’ conclusions. Future research should focus on areas that remain underdeveloped, including the effect of pre-exercise stretching for high impact sports and when a patient is injured, as well as the effects of regular stretching (after exercise, outside periods of exercise) on injury.
For a detailed look at stretching turn to Chapter 15, Principles of rehabilitation, in Clinical Sports Medicine.