Stretching Before and After Exercise: Effect on Muscle Soreness and Injury Risk

Reference: Herbert RD, Gabriel M. Effects of stretching before and after exercise on muscle soreness and risk of injury: systematic review. BMJ. 2002;325:468.Clinical Question: Among physically active individuals, does stretching before and after exercise affect muscle soreness and risk of injury?Data Sources: Studies were identified by searching MEDLINE (1966–February 2000), EMBASE (1988–February 2000), CINAHL (1982–1999), SPORT Discus (1949–1999), and PEDro (to February 2000). I searched the reference lists of identified studies manually until no further studies were identified. The search terms stretch, exercise, warm-up, and cool down were used in all databases except MEDLINE. In MEDLINE, an optimized OVID search strategy was used. This strategy included the terms searched in the other databases as well as terms such as flexibility, athletic injuries, sports, soreness, and muscle.Study Selection: The search was limited to English-language articles obtained from the electronic searches and the subsequent manual searches. This review included randomized or quasirandomized investigations that studied the effects of any stretching technique, before or after exercise, on delayed-onset muscle soreness, risk of injury, or athletic performance. Studies were included only if stretching occurred immediately before or after exercising.Data Extraction: Data extraction and assessment of study quality were well described. The principal outcome measures were measurements of muscle soreness and indices of injury risk. Results from the soreness studies were pooled by converting the numeric scores to percentages of the maximum possible score. These data were then reported as millimeters on a 100-mm visual analogue scale. Results of comparable studies were pooled using a fixed-effects model meta-analysis. Survival analysis using a Cox regression model was calculated on the time-to-event (injury) data.Main Results: The total number of articles identified using the search criteria was not provided; however, 5 studies on stretching and muscle soreness met inclusion and exclusion criteria. All of the studies meeting the criteria employed static stretching. One group reported the findings from 2 experiments, resulting in 6 studies meeting the inclusion and exclusion criteria. For the risk of injury, 2 studies, both investigating lower extremity injury risk in army recruits undergoing 12 weeks of basic training, met inclusion and exclusion criteria. On the basis of the PEDro scale, the methodologic quality of the studies included in the review was moderate (range, 2–7 of 10), with a mean of 4.1. For the studies on muscle soreness, 3 groups evaluated postexercise stretching, whereas 2 evaluated preexercise stretching. The participant characteristics from the 5 studies were noted to be reasonably homogeneous. Subjects in all studies were healthy young adults between the ages of 18 and 40 years (inclusive). For all studies but one, total stretching time per session ranged from 300 to 600 seconds. The exception was one study in which total stretching time was 80 seconds. Data from 77 subjects were pooled for the meta-analysis of muscle soreness outcomes at 24, 48, and 72 hours after exercising. At 24 hours postexercise, the pooled mean effect of stretching after exercise was −0.9 mm (on a 100-mm scale; negative values favor stretching), with a 95% confidence interval (CI) of −4.4 to 2.6 mm. At 48 hours, the pooled mean effect was 0.3 mm (95% CI = −4.0 to 4.5 mm), whereas at 72 hours, the pooled mean effect was −1.6 mm (95% CI = −5.9 to 2.6 mm). In each of these analyses, the results were not statistically significant in favor of either stretching or not stretching. For the studies on risk of lower extremity injury, the authors provided time-to-event (injury) data from 2630 subjects (65 military trainee platoons). These data were then combined and resulted in the allocation of 1284 subjects to stretching groups and 1346 subjects to control groups. The survival analysis identified a pooled estimate of the all-injuries hazard ratio of 0.95 (ie, a 5% decrease in injury risk; 95% CI = 0.78 to 1.16), which was not statistically significant.Conclusions: The data on stretching and muscle soreness indicate that, on average, individuals will observe a reduction in soreness of less than 2 mm on a 100-mm scale during the 72 hours after exercise. With respect to risk of injury, the combined risk reduction of 5% indicates that the stretching protocols used in these studies do not meaningfully reduce lower extremity injury risk of army recruits undergoing military training.