In Swimming, the human body must develop enough propulsive force to counterbalance the active drag of water. Various methods have been applied to ascertain this active drag, but they invariably necessitated cumbersome devices. The purpose of this study is to determine the active drag by use of self-developed transportable towing device that could be used in any swimming pool, and to evaluate training effects of a swimmer by the active drag index.
　Twenty-seven competitive swimmers (18 males and 9 females) volunteered to participate in this study. Subjects were towed with this device for a. distance of 20 meters at speeds higher than those of their free swimming speed. Thus the towing force was measured both in the gliding position and the crawl stroke movement. The active darg in the crawl stroke movement regressed as an exponential function of velocity.
　Their active drags were found to increase exponentially as the swimming velocity increase. The mean drag coefficient (k) was 3.554 ± 1.166, and mean exponent (n) was 2.07 ± 0.387. There were significant relationships between the drag coefficient and the girth of upper arm, the percentage body fat.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE