Ten prepubertal girls and 15 young women were tested for maximal torque, peak rate of torque development, electro-mechanical delay (EMD), and time to peak rate of torque development during isometric elbow flexion. Absolute peak torque (17.0 +/- 7.7 vs. 40.5 +/- 8.3 Nm) and peak rate of torque development (105.9 +/- 58.6 vs. 297.2 +/- 113.0 Nm s(-1)) were lower in the girls (p < .05). Normalized to muscle cross sectional area, torque was similar (8.27 +/- 2.74 vs. 8.44 +/- 1.65 Nm cm(-2)), as was peak rate of torque development, normalized to peak torque (6.21 +/- 1.94 vs. 7.30 +/- 2.26 Nm s(-1)/ Nm). Both, time to peak rate of torque development (123.8 +/- 36.0 vs. 110.5 +/- 52.6 ms) and EMD (73.2 +/- 28.6 vs. 51.9 +/- 25.6 ms), were longer in the girls, although EMD's difference only approached statistical significance (p = .06). Age-related isometric strength differences in females appear to be mainly muscle-size dependent. However, the time to peak torque and EMD findings suggest differential motor-unit activation which may functionally manifest itself in fast dynamic contractions.