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In brief: Forty-seven male police officers (mean age 41.0 years) were randomly assigned to three exercise groups: unsupervised, supervised, and control. Training consisted of walking and jogging three days per week for 20 weeks. The attrition rate for the unsupervised group (35%) was lower than for the supervised group (45%). The main reason the subjects gave for dropping out was lack of time. Both groups increased significantly compared to the control group in treadmill performance time, maximum oxygen uptake, and maximum oxygen pulse; and decreased significantly in resting heart rate, heart rate response to a step test, percent body fat, total skinfold fat, and waist girth.
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Gettman et al. (1983) studied this question.
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