On average, the runners ran 3.4 percent farther in the non-stretching performance test than they ran in the post-stretching performance test. Yet while they ran farther after not stretching, they burned 5 percent fewer calories, indicating that pre-run static stretching sabotaged running performance by reducing running economy. These results were published in the Journal of Strength and Conditioning Research.
Why would a static stretching warm-up make you run less efficiently? The authors of previous studies have speculated that static stretching warm-ups temporarily reduce musculoskeletal stiffness. While the word “stiffness” generally has negative associations with respect to athletic performance, a certain type of stiffness is beneficial to running performance. When you run, your legs function as springs that repeatedly bouncing off the ground, capturing “free” energy (i.e. energy that the body does not have to generate for itself) from each impact and using it to for forward thrust. Just as a loose mechanical spring (think of a worn automobile shock absorber) is less effective than a stiffer one, a less stiff leg (resulting from laxity at key muscle-tendon junctions) bounces less effectively off the ground during running. Consequently, the leg captures less “free” energy from the round and running economy is reduced.