Evidence-based Sports Medicine

Does stretching help prevent injuries?Long-term effectsAlthough the immediate effects of a single stretching sessionproduce a decrease in visco-elasticity and an increase in stretchtolerance, the effect of stretching over 3–4 weeks appears to affectonly stretch tolerance with no change in visco-elasticity. 21,29 In thiscase, a second explanation for the increased stretch tolerance besidesan analgesic effect is possible; regular stretching may induce musclehypertrophy.Animal research has shown that muscles that are stretched for24 hours per day for several days will actually increase in crosssectional area (or decrease in cross sectional area less than if castedwithout stretch) even though they are not contracting. 30–32 This isknown as stretch induced hypertrophy. These studies all usedcast immobilisation 30,32 or weights to continuously stretch the muscle24 hours/day over 3–30 days. 31 This is of course very different fromhuman stretching programmes that involve stretching for only30–60 sec/day for any particular muscle group. Still, if the shorterduration human stretches are continued over months, there remainsthe possibility that some hypertrophy will occur.If stretch induced hypertrophy does occur, it should be associatedwith an increase in stiffness because of the increased muscle crosssectional area. For example, the stiffness of an elastic band doubles ifyou double the cross sectional of an elastic band by folding it uponitself, even though the elastic itself has not changed. Therefore, athicker muscle should also be stiffer. However, the stiffness of humanmuscles does not change over time with stretching. 21,29 Therefore, ifstretch induced hypertrophy is occurring in this situation, then theremust be associated changes in the visco-elastic properties of theindividual muscle fibers to explain the lack of increase in wholemuscle visco-elasticity. Much more research is needed to answer thesequestions.Does stretching immediately before exerciseprevent injury?MethodsThe Medline database was searched for all clinical articles relatedto stretching and injury using the strategy outlined in Table 7.1. Alltitles were scanned and the abstracts of any potentially relevantarticles were retrieved for review. All studies that used stretching as anintervention, included a comparison group, and had some form of101