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

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Abstract
Of 12 healthy men with a mean age 50 .+-. 4 yr who were on bed rest for 10 days, 6 were randomly assigned to perform individually prescribed physical exercise daily for 60 days after bed rest (exercise group) and 6 simply resumed their customary activities (control group). Exercise group subjects were significantly more active than control subjects during this interval (P < 0.05). 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 O2 consumption increased by 4.8 .+-. 4.2 vs. 2.2 .+-. 5.0 ml/kg per min (both P < 0.05). Despite these differences in the cardiovascular response to exercise, peak O2 consumption in both groups returned to before-bed rest levels by 30 days after bed rest, and this was accompanied by significant (P < 0.05) 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. [The risks associated with post myocardial infarction exercise are discussed.].