1. Submaximal bicycle exercise tests have been performed in nine healthy men on seven annual occasions between the ages of 64 and 70 years. Ten younger men (average age 33 years) have also been studied once for comparison.
2. The ventilatory cost of submaximal work at V̇o2 = 1 litre/min rises significantly from 24.3 ±0.8 litres/min at age 64 years to 31.8 ± 1.8 litres/min at age 70 years; the latter value differs significantly from that of the young men (25.6 ± 0.9 litres/min). Similar changes are seen in the ventilation at 75 W and at V̇co2 = 1 litre/min. The rate of change, between 3% and 5% per year, is considerably greater than that found for the change with age in cross-sectional studies of younger men. There is also a rise in the respiratory quotient, consistent with the hyperventilation found.
3. The cardiac frequency at 1 litre/min also rose with age in the older men, and rough estimates of the decline in their aerobic capacity suggest that progressive anaerobiosis could account for at least some of this increase in ventilation seen during submaximal work.