Exercise conditioning in middle-aged men after 10 days of bed rest.

Of 12 healthy men with a mean age 50 +/- 4 years who had been at bed rest for 10 days, six were randomly assigned to perform individually prescribed physical exercise daily for 60 days after bed rest (exercise group) and six simply resumed their customary activities (control group). Exercise group subjects were significantly more active than control subjects during this interval (p less than .05). Two classic training effects observed in the 60 days after bed rest were significantly larger among exercise than among control group subjects; compared with values immediately after bed rest, heart rate at a constant submaximal workload declined by 36 +/- 11 beats/min in the exercise group vs 16 +/- 8 beats/min in the control group and peak oxygen consumption increased by 4.8 +/- 4.2 vs 2.2 +/- 5.0 ml/kg/min (both p less than .05). Despite these differences in the cardiovascular response to exercise, peak oxygen consumption in both groups returned to before-bed rest levels by 30 days after bed rest, and this was accompanied by significant (p less than .05) and similar increases in resting left ventricular end-diastolic and stroke volumes in both groups. Simple resumption of usual physical activities after bed rest was as effective as formal exercise conditioning in restoring functional capacity to before-bed rest levels.