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ABSTRACT.
Harris, N.K., J.B. Cronin, and W.G. Hopkins. Power outputs of a machine squat-jump across a spectrum of loads. J. Strength Cond. Res. 21(4):1260-1264. 2007.-The load that maximizes mechanical power output (Pmax) has received considerable research attention owing to its perceived importance to training prescription. However, it may be that identifying Pmax is of little importance if the difference in power output about Pmax is insubstantial. Additionally, comparing the effect of load on power output between studies is problematic due to various methodological differences. The purpose of this study therefore was to quantify the concentric power output for a machine squat-jump across a spectrum of loads (10-100% of 1 repetition maximum [1RM]). To estimate Pmax load and proximate loads a quadratic was fitted to the power output (Watts) and load (% of 1RM) of 18 well-trained rugby athletes. Pmax for peak and mean power output occurred at 21.6 ± 7.1% of 1RM (mean ± SD) and 39.0 ± 8.6% of 1RM, respectively. A 20% change in load either side of the maximum resulted in a mean decrease of only 9.9% (90% confidence limits ±2.4%) and 5.4% (±0.9%) in peak and mean power respectively; standard deviations about these means (representing individual differences in the decrease) were 6.0% and 2.1%, respectively (90% confidence limits ×/÷1.34). It appears that most athletes have a broad peak in their power profile for peak or mean power. The preoccupation of identifying one load for maximizing power output would seem less meaningful than many practitioners and scientists believe.
KEY WORDS. resistance training, optimal load, kinematics, kinetics
INTRODUCTION
Power can be defined as the rate at which mechanical work is performed or as the product of force and velocity, and is commonly perceived to be critical to the performance of many athletic tasks (1, 18, 31). Consequently the development of power has been the subject of much research and subsequent conjecture, particularly the improvement of power through the use of resistance strength training (RST). Of interest to strength and conditioning practitioners is identifying the load that maximizes peak and mean power output (Pmax) (12, 19, 26, 38). In terms of the point on the power-load spectrum where Pmax occurs (Pmax load), some researches (3, 33) have suggested that power output at loads...