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The evidence is starting to pile up against static stretching (where you hold a stretch as opposed to moving, “dynamic” stretches) before workouts. Studies in the past have found that it negatively affects strength and power, specifically for short, sprinting efforts.
But in a study published in the June 2014 issue of PLOS One, researchers from the University of São Paulo in Brazil looked into its effect on the pacing strategy of distance runners. The study took 11 recreational long-distance runners, who underwent lab tests and 3K time trials on an outdoor 400-meter track (with and without stretching beforehand) over a span of three weeks. The researchers had the participants perform seven different lower-body stretches, each done three times and held for 30 seconds.
The study showed that static stretching before a run did not affect performance (the overall time differences weren’t significant); however, it resulted in slower acceleration as well as higher perceived efforts for the first 800 meters—the runners started out slower yet felt like they were working harder after stretching. In addition, researchers found a 9.2 percent decrease in drop-jump height (a way to measure explosive power) after stretching—researchers concluded that static stretching resulted in “a reduced capacity of the skeletal muscle to produce explosive force.”
While the study only included recreational (not highly trained) runners, and their total time spent stretching added up to about 20 minutes (not very realistic), and it suggests that total run performance wasn’t affected, it still poses the question: Why do static stretching before a run if it makes you start slower and feel like you’re working harder? Instead, save that stretching time for post-run, when it’s been shown to be the most beneficial—decreasing soreness and preventing injury.