Or at least unbeneficial. A comprehensive study out of Croatia complements other evidence that stretching your muscles before exercise results in less strength, power, and performance than if you hadn’t stretched.
The numbers, especially for competitive athletes, are sobering. According to their calculations, static stretching reduces strength in the stretched muscles by almost 5.5 percent, with the impact increasing in people who hold individual stretches for 90 seconds or more. While the effect is reduced somewhat when people’s stretches last less than 45 seconds, stretched muscles are, in general, substantially less strong.
They also are less powerful, with power being a measure of the muscle’s ability to produce force during contractions, according to Goran Markovic, a professor of kinesiology at the University of Zagreb and the study’s senior author. In Dr. Markovic and his colleagues’ re-analysis of past data, they determined that muscle power generally falls by about 2 percent after stretching.
And as a result, they found, explosive muscular performance also drops off significantly, by as much as 2.8 percent. That means that someone trying to burst from the starting blocks, blast out a ballistic first tennis serve, clean and jerk a laden barbell, block a basketball shot, or even tick off a fleet opening mile in a marathon will be ill served by stretching first. Their performance after warming up with stretching is likely to be worse than if they hadn’t warmed up at all.