PURPOSE: To determine whether knee extensor power asymmetry limits functional mobility of older adults who possess muscle weakness. METHODS: Knee extensor power was measured in 36 older men and women (76.0±7.6yr), for each leg, on an isokinetic dynamometer at 60, 180, and 300degs-1 and power asymmetry was calculated as the percent difference in power between strong and weak legs, at each isokinetic velocity. 400-m walk, stair ascent, and five-repetition chair rise tests were performed to assess functional mobility. Pearson correlations were used to examine the relationship between weak leg power, strong leg power, power asymmetry, and 400-m walk time, stair ascent time, and chair rise time. Participants were then stratified into low power-high asymmetry (LP-HA), low power-low asymmetry (LP-LA), high power-high asymmetry (HP-HA), and high power-low asymmetry (HP-LA) groups who were compared for functional mobility. RESULTS: Knee extensor power asymmetry was unrelated to 400-m walk time (r=0.16, p=0.180), stair ascent time (r=0.22, p=0.094), or chair rise time (r=0.03, p=0.437), whereas weak and strong leg powers were equally associated with 400-m time (r=-0.62, p<0.001; r=-0.62, p<0.001), stair ascent time (r=-0.55, p<0.001; r=-0.57, p<0.001), and chair rise time (r=-0.28, p=0.048; r=-0.31, p=0.032), respectively. Power asymmetry was lowest at 60degs-1 (12%), and increased with contraction velocity (p=0.001) to 15% at 180degs-1 and to 20% at 300degs-1. LP-HA exhibited 26% slower 400-walk time than HP-LA (p=0.015) and 19% slower than HP-HA (p=0.037). LP-HA had 31% slower stair ascent time than HP-LA (p=0.033). There were no differences in chair rise performance between groups. CONCLUSIONS: Knee extensor power asymmetry was unrelated to 400-m walk, stair ascent, and chair rise performance in older adults. Weak and strong limb powers were equally related to these functional measures, but a leftward shift of the power-mobility curve exists for the weak leg that may hinder clinical assessment if strength or power is measured on a single limb and symmetry is assumed. The greatest degree of knee extensor power asymmetry occurred at the fastest isokinetic velocity, which suggests high-speed muscle contractions may better differentiate laterality of function in older individuals.