1. Fifty males and 50 females, 15-71 years of age, exercised maximally for 30 s on an isokinetic ergometer at a pedalling frequency of 60 rev./min. Results were compared with maximal oxygen uptake (VO2 max.) obtained in a progressive incremental exercise test.

2. Total work in 30 s was higher in males than females, declined linearly by about 6% per decade of age (r = −0.65), and was related closely to height (r = 0.75) and to lean thigh volume estimated anthropometrically (r = 0.84). A close association with vital capacity (r = 0.86) was also found that accounted statistically for the combined effects of age and height.

3. The percentage decline in power during 30 s (fatigue index) was lower in subjects reporting greater leisure activity.

4. A close relationship was found between total work in 30 s and Vo2 max. (r = 0.86), with vital capacity and leisure activity exerting additional influences on Vo2 max. (P < 0.001; multiple r = 0.93).

5. The well-established reduction with age in Vo2 max. is associated with an apparent parallel reduction in the power output capacity of large muscle groups recruited in heavy dynamic leg exercise.

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