Research in exercise training of healthy persons, which has been conducted almost exclusively in supervised group programs, is relatively expensive for the investigator and inconvenient for the participant. To overcome these obstacles, self-monitored moderate-intensity home-based exercise training was prescribed for 28 middle-aged men and 26 middle-aged women. The median energy expenditure prescribed for each of 5 weekly exercise sessions was 4 cal/kg body weight, or 317 kcal for men and 265 kcal for women, corresponding to a median duration of 45 and 60 minutes, respectively. In the next 24 weeks, peak oxygen uptake increased 13.7% in men who exercised, from 31 +/- 4 to 37 +/- 4 ml/kg/min, and 10% in women who exercised, from 26 +/- 4 to 29 +/- 5 ml/kg/min (p less than 0.001 for both comparisons). The proportion of prescribed caloric expenditure per session, which was documented by a solid-state heart rate recorder, was 108% in men and 90% in women. The duration of training at heart rates above the prescribed range approximated 10 minutes per session for both men and women; the proportion of total caloric expenditure represented by exercise at heart rates exceeding the prescribed limit was 9% for men and 4% for women. The proportion of time spent within the prescribed heart rate range during training sessions was 76% for men and 84% for women. Training-induced musculoskeletal problems were reported by 6 men and no women. No subject sought medical attention and all resumed training within 1 week.(ABSTRACT TRUNCATED AT 250 WORDS)