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To determine sex and race differences in muscle power per unit of muscle contraction, knee-extensor muscle power normalized for knee-extensor muscle volume was measured in 79 middle-aged and older adults (30 men and 49 women, age range 50–85 years). Results revealed that women displayed a 38% faster peak movement velocity than men and African Americans had a 14% lower peak movement velocity than Whites of a similar age when expressed per unit of involved muscle (p < .001). As expected, men exhibited greater knee-extensor strength and peak power per unit of muscle than women, but women had a faster knee-extension movement velocity per unit of muscle than men at the same relative strength level. Moreover, African Americans had greater knee-extensor muscle volume than Whites but exhibited lower knee-extensor strength and lower movement velocity per unit of muscle when tested at the same relative strength levels.

Doldo, Delmonico, Bailey, Hand, Kostek, Rabon-Stith, Menon, and Hurley are with the Dept. of Kinesiology, University Of Maryland, College Park, MD 20742. Conway is with the USDA, ARS, BHNRC, Diet and Human Performance Laboratory, Beltsville, MD 20705. Carignan is with the Dept. of Aerospace Engineering, Space Systems Laboratory, University of Maryland, College Park, MD 20742.