EFFECTS OF GENDER AND THE LEWIS FORMULA IN MECHANICAL POWER ESTIMATES

Abstract

One of the simplest way to calculate power-output is using the Lewis formula. Harman et al. (1991) and Garhammer (1993) stated that the Lewis formula is not scientifically correct but it still widely used. Only a limited number of studies have tried to determine if there is a need for separate power-output prediction equations for each gender (Mayhew & Salm, 1990; Garhammer, 1993). The purpose of this study was to determine the need of separate power-output prediction equations for each gender and to test the validity of Lewis formula in the prediction of power output. Forty-nine female and 69 male athletes were measured for height, weight, thigh circumference, thigh skinfold, thigh length, and foreleg length. The athletes performed a countermovement jump and reach test from a force platform. A Vertec jumping apparatus was used to measure vertical jump height 0an d the force platform was used to acquire force-time data to determine actual peak and average power output. Eight anthropometric measurements, VHJ, and gender were used in a stepwise multiple regression statistical procedure to develop the prediction equations. One way ANOVA with repeated measures was used to compare the predicted average power from the Lewis formula, the estimated average power values developed in this study, and the actual average power values measured. There were significant differences (p<.05) between gender for peak and average mechanical power (5,782 ±1,123 and 3,037 ±638 for men and 3,285 ± 563 and 1,828 ± 351 for women). When the gender variable was forced first in the stepwise multiple regression equation it produced an adjusted r2 = .64 and .55 for peak and average power, respectively. The gender effect was practically eliminated by the effects of VHJ, body mass, and height. These variables were the only significant variables (pC.05) selected by the step-wise multiple regression to predict both peak and average mechanical power. These variables accounted for 91 and 82% of the variance in peak and average power output, respectively. The power-output values produced using the Lewis formula under predicted the average power-output values and were significantly different from the actual and the estimated values measured in this study. The results indicate that VHJ, body mass, and height are good predictors of peak and average power output in college athletes. Perhaps the difference in genders is the result of size and strength rather than a male and female quality. The predictions equations developed in this study can be used to monitor athletic performance, analyze injury rehabilitation, and aid in team selection.