Contraction work (CW) and peak torque (PT) of maximum isokinetic plantar flexions were measured in clinically healthy subjects randomly chosen from the official census list of Umeå, Sweden, in three groups: 40-44, 50-54 and 60-64 years of age, with similar proportions of men and women. Maximum isokinetic plantar-flexions were performed at angular velocities of 30, 60, 120 and 180 degrees X s-1. Body-weight, height and crural circumference were measured. Subjects rated their levels of leisure and occupational activities. To establish formulae to predict CW and PT, stepwise regression procedures were applied. The predictive powers (r2) of the formulae which incorporated age, sex and crural circumference, were higher for PT (30 degrees X s-1: 0.82, 60 degrees X s-1: 0.79, 120 degrees X s-1: 0.75, 180 degrees X s-1: 0.56) than for CW (30 degrees s-1: 0.63, 60 degrees s-1: 0.63, 120 degrees s-1: 0.60, 180 degrees s-1: 0.52). Thus the part of the variance explained decreased with increasing angular velocity, but more than 50% was still explained at 180 degrees s-1. The results indicate that the mechanical output of the plantar flexors is predictable.
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