This study was aimed to investigate the influences of age and gender on isometric muscle torque and explosive muscle power output with reference to muscle volume. A total of 177 healthy subjects of both genders were divided into four groups according to their age and gender : 46 young men (22.0±3.2yrs), 43 young women (22.7±3.3yrs), 46 elderly men (71.2±4.3yrs) and 42 elderly women (72.7±4.5 yrs) . The maximal voluntary isometric knee extension torque of the right leg (hip and knee angle at 90 degrees) and the power of bilateral leg extension in sitting position were mea sured. The ratios of both torque and power to muscle volume, estimated using ultrasonograph measurement, was calculated (torque/MV and power/MV respectively) . Torque was significantly less among the elderly than among the young for both genders, and among women than among the men for both age groups. Significant age-related differences were evident even in terms of torque/ MV, but the corresponding differences between men and women disappeared. On the other hand, power MV showed significant age- and gender-related differences, and the age-related difference was larger than that for torque MV. These results suggest that age- and gender-related differences in power are more noticeable than differences in torque and that these differences are not simply explained by differences in muscle volume.