RELATIONSHIP BETWEEN KNEE EXTENSOR MUSCLE STRENGTH AND MOVEMENT PERFORMANCE: THE EFFECT OF LOAD AND BODY SIZE

The main aim of the present study was to evaluate the effect of external loading on the relationship between leg muscle strength and vertical jump performance. Sixty-six physically active men performed maximal countermovement jumps (CMJ) under five loading conditions: body weight (BW), negative loads (85% BW and 70% BW) and positive loads (115% BW and 130% BW), on a force plate. CMJ was followed by the measurement of subjects' maximal concentric knee extension torque at 60 degrees s(-1) by an isokinetic dynamometer. The relationship between knee extensor strength and jumping performance with various loads was assessed by Pearson's correlation coefficients and partial correlation coefficients after controlling for body mass. Knee extensor muscle strength correlated significantly (r=.78-.79; all p<.01) with peak power output during CMJ under all loading conditions. Considerably lower correlation coefficients (r=.18-.43; p=.01-.15) were observed between knee extensor strength and CMJ height under all loading conditions, which tended to be higher after the effect of body mass had been removed (r=.37-.51; all p<.01). These results contradict the general belief that an increase in external load is associated with the increased role of leg muscle strength in maximizing power output and jump height. Furthermore, the results suggest that relative strength is a better predictor of jumping performance than absolute strength, independently of external loads used.