The difference between the upper limbs and the lower limbs in individuals on force output characteristics during stretch-shortening cycle movement

Abstract

A study was conducted to investigate the difference between force output characteristics of the upper and lower limbs in individuals focusing on limb stiffness using a mass-spring model during exercise. Fourteen trained males performed purely concentric (PC) exercise and two kinds of stretch-shortening cycle (SSC) exercises (counter movement, rebound movement) for both the upper limbs (push-up) and lower limbs (jump). Upper and lower limb forces were assessed using the mean force generated during the concentric phase of each exercise. Pre-stretch augmentation (augmentation) was defined as the ratio of the mean force of SSC exercise to the mean force of PC exercise. Upper and lower limb stiffnesses were calculated as the mean force divided by the vertical displacement during the eccentric phase of SSC exercise. The results were as follows: 1) Mean force of SSC exercises were significantly higher than that of PC exercise in both upper and lower limbs. However, augmentation was much higher in the lower limbs than in the upper limbs. 2) There were significant negative correlations between stiffness and mean force (r=-0.661, p<0.05), and stiffness and augmentation (r=-0.743, p<0.01) during rebound push-up. In contrast, there were significant positive correlations between stiffness and mean force (r=0.680, p<0.05), and stiffness and augmentation (r=0.782, p<0.01) during rebound jump. 3) There was a significant correlation between upper mean force and lower mean force during PC exercise (r=0.607, p<0.05). However, there were no significant correlations in counter movement (r=-0.092, ns) and rebound exercise (r=-0.278, ns). These results indicate that ability to utilize the benefit of SSC movements and optimum limb stiffness for forceoutput are different in the upper and lower limbs, and that the force output characteristics of the upper and lower limbs vary in each individual during SSC movement.