One of the justifications for stretching is that it improves flexibility. This study says that the less flexible a runner is the better is his running economy.
Sit-and-Reach Flexibility and Running Economy of Men and Women Collegiate Distance Runners.
Flexibility has been controversially suggested as one of the biomechanical factors contributing to the variability observed in running economy among distance runners. The purpose of this investigation was to determine the magnitude of the relationship between sit-and-reach flexibility and running economy in men and women. Eight collegiate distance runners (4 men and 4 women) served as subjects for this correlational study (age = 19.9 +/- 1.25 years; &OV0312;o2max = 63.2 +/- 3.4 ml.kg.min). Each subject's flexibility was measured using the standard sit-and-reach test, and running economy was recorded during an incremental maximal treadmill test at both absolute (men = 241.2 m.min; women = 198.32 m.min) and relative (10-km pace) velocities. Statistical analyses indicated a significant relationship between sit-and-reach scores and running economy at an absolute velocity, as well as a significant sex difference in sit-and-reach scores. The significant relationship demonstrates that the less flexible distance runners tended to be more economical, possibly as a result of the energy-efficient function of the elastic components in the muscles and tendons during the stretch-shortening cycle.