The purpose of this study was to quantify the effects of ageing on the maximal power (P_max) of the elbow flexor muscles and to determine the impact of velocity on the loss of power in older people. Sixteen elderly subjects (7 men and 9 women, age range 61-78 years) and 17 young subjects (11 men and 6 women, age range 18-27 years) participated in this study. Maximal elbow flexions were performed against increasing inertia. The maximal force (F_max), maximal shortening velocity (V_max), P_max, dynamic constants (a, b and a/F_max), optimal force (F_opt), optimal velocity (V_opt) and V_opt/V_max were determined from Hill's equation. Myoelectrical activity (EMG) of the biceps and triceps muscles was quantified as an root mean square (RMS) value. F_max, V_max, P_max, F_opt, and V_opt were significantly lower in elderly than in young subjects (28, 31, 45, 24 and 28% lower, respectively; p<0.05), whereas a/F_max and V_opt/V_max were not different between the two age groups. In women, the greater decrease in P_max appears to be more dependent on V_opt than F_opt. In addition, V_max decreased with age in women but not in men. The absence of significant differences between age groups in normalised RMS values indicates that P_max and V_max loss with increasing age could result more from changes in the properties of contractile element than from changes in muscular activity.