That is the question. Researchers at Florida State University may have an answer.
Ten trained male runners participated in the study. On separate occasions, they ran for one hour on a treadmill, beginning with 30 minutes at a moderate pace and ending with a 30-minute performance test wherein the runners were instructed to cover as much distance as possible. The runners performed 16 minutes of static stretch for the major muscle groups of the lower body before one of the runs and just sat around for 16 minutes before the other.
The results? When the runners didn’t stretch they ran farther and burned fewer calories in the process. Stretching reduced efficiency! Turns out, runners’ legs are like shock absorbers; stiffer ones work better, helping the body recapture energy with each foot fall.
Stretching may slow me down by 3.4%, but I don’t plan on giving it up anytime soon. For me it’s not a matter of maximum efficiency (I don’t mind burning the extra calories). It’s a matter of injury prevention.
Updated December 2, 2009: See also this New York Times article on a study at Nebraska Wesleyan University with similar results: tighter muscles performed more efficiently than loose ones. (Via Kathy, on dailymile)