Muscle Strength and Contractile Kinetics of Isometric Elbow Flexion in Girls and Women

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.