A Biomechanical Basis in the Human Movement With Great Force and Power : Effects of the Preliminary Force on Fast Isometric Force Development

Abstract

In the performance of a human movement that requires great force and power, exertion of a large amount of force from throughout the main phase is necessary. From the viewpoint of neuromuscular function, this means that guick force development, maintenance of the great force and prompt force release will be necessary to obtain good performance in the human which involve explosive movements activities. In the present study, the effects of the preliminary force on fast development of the isometric force were investigated in elbow flexion. Nineteen male varsity track and field athletes were instructed to exert their maximum force as fast as possible from preliminary force of 0, 20, 50 and 80 percent of maximum force. Sampling interval of force was 2/511 sec. and the force was stored in a digital wave memory device which later was printed out. The exponential equation described by Yoshimoto, et al. was used to evaluate the obtained force-time relationship. Some results and a suggestion were summarzied as follows: 1)The force-time relationship of elbow flexion could be fitted to the equation, F = Fo + (Fm-Fo) {1 - e^<λ(t-B)>}, where F: force (kg), Fo: preliminary force (kg), Fm: maximum force (kg), λ: inverse of characteristic time of force development (1/sec.), B : dead time (sec.), t: time (sec.), e: natural logarithmic base. 2)As the preliminary force increased, the slow developing portion of the early part of force-time curve became small, and in the case of the contraction from 80 percent preliminary force the slow developing portion almost disappeared. 3)The exerted maximum force increased with the increase in the preliminary force, while the differences of the maximum force among four contractions were not significant. However, the force from the start of force development to 0.2 sec. in the contraction from 50 or 80 percent preliminary force was significantly larger than those of 0 and 20 percent one. 4)As the pleliminary force increased, it was observed that dead time (B) decreased and inverse of characteristic time of force development(λ) increased. 5)Inverse of characteristic time of force development in the sprinters was considerably larger in the contraction from 80 percent preliminary force than those of the other preliminary ones, while such a result has not been presented by distance runners. 6)In the performance of a human movement that requires great force and power, it might be recommended to maintain some preliminary force, followed by a quick force development in the main phase of the movement.