LAS VEGAS - September 17, 2008 - Contrary to the prevailing idea that stretching enhances athletic performance, a new study by UNLV kinesiology researchers found that certain stretching may actually reduce performance by decreasing leg power.
The study, which appears in the September 2008 issue of the Journal of Strength and Conditioning Research, investigated how two typical stretching techniques for the hamstrings and quadriceps muscles in the legs affected measures of strength and power in a group of male and female athletes.
Specifically, participants were asked to perform a vertical jump and seated knee flex on three occasions after a typical duration of basic static (holding) and ballistic (bouncing) stretches, or no stretching at all. While little or no difference was found in vertical jump and leg torque, power measures for the stretching groups were significantly reduced.
"Athletes typically include static stretching as a part of the warm-up, but the evidence is clear that this practice will decrease performance in sports that require explosive movements," said UNLV kinesiology professor and study co-author Bill Holcomb, who directs the university's Sports Injury Research Center. "Developing flexibility is important for reducing sports injury, but the time to stretch is after, not before, performance."
Holcomb suggests that coaches limit stretch duration as a part of the warm up in most sports and refrain from pre-activity stretching altogether for sports that are reliant on maximum power. Instead, athletes should perform a whole-body warm-up activity followed by sport specific, or dynamic, stretching.
Power, calculated using a force-measuring device during the vertical jump testing, decreased between 2.4 and 3.4 percent after ballistic and static stretching. Vertical jump is commonly used in research as a predictor of power because the process of jumping requires a person to effectively generate force with their legs at rapid speed. Also, the hamstrings and quadriceps both function as major muscles used in jumping.
While the percentage of the power decrease may not warrant a change in warm up routine for recreational athletes, it is quite significant for competitive athletes participating in activities requiring maximum power, such as track and field and football, for example.
Participating in the study with Holcomb were UNLV Department of Kinesiology and Nutrition professors Mack Rubley and Mark Guadagnoli, and graduate kinesiology student Michelle Samuel. The study appeared in the September 2008 issue of the Journal of Strength and Conditioning Research and can be found online at: http://www.nsca-jscr.org.