Correlations between internal and external power outputs during weightlifting exercise

Identifying loads that maximize mechanical power is important because training at such loads may optimize gains in dynamic athletic performance. The purpose of this study was to examine correlations between measures of external mechanical power output and internal mechanical joint power output across different loads during a weightlifting exercise. Ten subjects performed 3 sets of the clean exercise at 65, 75, and 85% of 1 repetition maximum (1RM). Peak external mechanical power output was calculated with 4 commonly used methods, whereas an inverse dynamics approach was used to calculate peak internal mechanical power output for the hip, knee, and ankle joints along with the peak of the sum of all internal joint powers. All peak mechanical power outputs were expressed as relative peak power by either ratio (watts per kilogram) or allometrically scaling to body mass (W·kg). Correlation coefficients were used to compare power output measures. The greatest numbers of significant correlations between internal and external power outputs were observed at 85% of 1RM, at this load hip and knee joint power outputs were correlated to external mechanical power output when calculated with the traditional work-energy method. In addition, the peak sum of all mechanical joint powers was correlated to mechanical power output when calculated with the impulse-momentum method at loads of 75 and 85% of the 1RM. Allometric scaling of power outputs yielded one more significant correlation than did the ratio scaled power outputs. These findings support the use of the work-energy method when making inferences about internal joint powers from external power outputs when loads equal to 85% of 1RM are being lifted. In addition, the impulse-momentum method may be used to make inferences about the sum of all internal joint powers from external power outputs when loads between 75 and 85% of 1RM are being lifted.