Previous research has found that lower limb muscle asymmetries increase with age and are linked to fall and injury risks. However, past studies lack a wide variety of muscle function modes and measures as well as comparison to a comparable younger age group. The purpose of this study was to examine age-related lower limb muscle function asymmetries across a variety of muscle action types and velocities in young and old adults. Lower limb balance, strength, power, and velocity were evaluated with concentric, isometric, isotonic, and eccentric muscle actions during a single-leg stance test and on single- and multi-joint dynamometers in 29 young (age = 21.45 ± 3.02) and 23 old (age = 77.00 ± 4.60) recreationally active men and women. Most (15 of 17) variables showed no statistical (p > 0.05) or functional (10% threshold) limb asymmetry for either age group. There was a significant main effect (p = 0.046; collapsed across groups) found for asymmetry (dominant > non-dominant) for the isotonic peak velocity variable. There was a significant (p = 0.010) group × limb interaction for single-joint concentric peak power produced at a slow (60 deg/s) velocity due to the non-dominant limb of the young group being 12.2% greater than the dominant limb (p < 0.001), whereas the old group was not asymmetrical (p = 0.965). The findings of this investigation indicate there is largely no age-related asymmetry of the lower limbs across a range of muscle function-related variables and modes, with a couple of notable exceptions. Also, the significant asymmetries for the isotonic peak velocity variable perhaps show the sensitivity of this uncommonly used measure in detecting minimally present muscle function imbalances.

Post-activation performance enhancement (PAPE) is a phenomenon that can enhance muscle performance following maximal or near-maximal muscle actions. While the effects of concentric and isometric conditioning actions on PAPE have been studied, less is known about the influence of eccentric muscle actions. This study investigated the effects of a multi-joint eccentric overload (EOL) protocol on PAPE expressed through countermovement jump (CMJ) height and isokinetic peak force (PF) outcome measures. Twenty-eight recreationally trained participants (18–30 years) completed three visits in a randomized, counterbalanced design. Following familiarization, participants performed either an EOL protocol involving two sets of six maximal isokinetic eccentric actions or a control condition (CON) involving cycling. The CMJ and PF were assessed at baseline and 15 s, 5 min, and 10 min post-exercise. Results showed no significant condition × time interaction or main effect of condition for either CMJ or PF (p > 0.05). However, a significant main effect of time (collapsed across condition) was observed for CMJ (p = 0.019), with post hoc analyses revealing a significantly higher CMJ at 5 min post-exercise compared to 15 s post-exercise (p = 0.037). These findings suggest that this multi-joint eccentric protocol did not effectively elicit PAPE, and therefore may not be optimal for inducing acute performance enhancement. Future research should further elucidate the optimal eccentric loading parameters and muscle action types for inducing PAPE.