To determine sex and race differences in strength, muscle power, movement velocity, and functional ability, knee extensor strength and muscle power normalized for muscle volume was measured in 79 middle-aged and older adults (30 men and 49 women, age range 50-85 yrs). Results indicated that men had 55% greater muscle volume (MV; P < 0.001), 24% greater 1 RM strength (P < 0.01), 9% greater muscle quality (MQ; 1 RM/MV; P < 0.05), 26% greater peak muscle power (PP; P < 0.01), and 14% greater MPQ (PP/MV; P < 0.001) than women. However, women displayed a 38% faster peak movement velocity than men when expressed per unit of muscle (movement velocity quality) (PV/MV; P < 0.001). Race analysis showed that African Americans had 20% greater MV than Caucasians (P < 0.001), but 11% lower MQ (P < 0.01) and a 17% lower PV/MV (P < 0.05) than Caucasians of similar age. Men displayed a 22% faster stair climb time than women, while Caucasians exhibited 19% and 16% faster times in rapid pace gait and 8-ft up-and-go, respectively. Thus, despite greater strength and power per unit of muscle in men, women have a faster knee movement velocity per unit of muscle than men. Moreover, African Americans have greater knee extensor muscle volume than Caucasians, but exhibit lower muscle quality and movement velocity quality.