The Age-related Changes In Multi- And Single-joint Measures Of Power Output

Abstract

Many previous studies have demonstrated age-related reductions in power output. However, few studies have identified if the age-related declines in power output during a functional lower body movement are similar to single-joint isokinetic testing. PURPOSE: To compare the relationships between the age-related reduction in power output using a single-joint isokinetic muscle action versus a more functional multi-joint vertical jump (VJ) assessment. METHODS: Forty middle- to older-aged men (mean±SD; age=59.2±7.8 years; range= 50-74 years) visited the lab on two occasions, separated by 48-72 hours. During the second visit, and following a familiarization session on visit one, participants performed 2-3 maximal countermovement VJ attempts while attached to commercially available equipment designed to examine lower body power output. The equipment was placed on the floor behind the subject to allow the cord to be extended without impeding the VJ technique. Following the VJ assessment, the participants performed three maximal concentric isokinetic muscle actions of the right leg extensors at 240°·sec-1 using a calibrated isokinetic dynamometer. The torque and position signals were sampled from the dynamometer at 2 kHz and were processed offline using custom written software. Isokinetic mean power (MP) was calculated as the product of the average torque (Nm) during the load range and isokinetic velocity (°·sec-1). Pearson correlation coefficients (r) were used to evaluate the relationships between age and VJ, and age and isokinetic MP. The Steiger Z calculation and an effect size was used to determine the difference between the relationships. The alpha level was set at P≤0.05. RESULTS: There were significant relationships between age and VJ power output (r=-0.633; P<0.001) and age and isokinetic MP (r=-0.410; P=0.009). The correlation coefficients were similar (P=0.112), however, there is a moderate difference (effect size=0.31) between the relationships. CONCLUSIONS: Single-joint isokinetic power output may demonstrate a weaker, but similar relationship with age when compared with more functional VJ assessments.