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The historic studies by Robinson and Astrand as well as more recent studies present a fairly uniform rate of decline in VO2max with age at 0.40-0.50 ml X kg-1 X min-1 X year-1 in men. In women the rate of decline appears to be less--approximately 0.20-0.35 ml X kg-1 X min-1 X year-1, at least in cross-sectional studies. Further, there is no clear distinction in the rate of change in VO2max when comparing active and inactive populations. Longitudinal studies varying from 2.5 to 21 to 56 years present a confounding picture. The rate of decline in VO2max varies from 0.04 to 1.43 ml X kg-1 X min-1 X year-1. There is some indication that active individuals decline at a slower rate than inactive persons but the results are not uniform. A possible explanation is that changes in VO2max over the entire age range may be curvilinear, with active individuals declining slowly as long as they maintain a regular exercise program, and sedentary individuals declining at a rapid rate during their 20's and 30's followed by a slower rate of decline of their VO2max as they age further.

Studies of chronic disease may require long-term observation of volunteer participants. This is a characteristic of investigations of primary or secondary prevention of cardiovascular disease by increased level of physical activity. Activation of sedentary, middle-aged, high risk men requires a substantial personal commitment on their part to a long-term programme. Because of self-selection, individuals who volunteer for such programmes cannot be assumed to be representative of the populations from which they come. To the best of our knowledge, there has been no systematic investigation of such self-selection based upon a study designed for that purpose. We found little consistent tendency for vouunteering behaviour to be associated with serum cholesterol, blood pressure, relative weight, level of activity at work, or Type A hehaviour variables.

Eight healthy young men (ages 19–35), four older men (ages 38–42), three obese subjects (two women and one man, ages 20–34) were individually exposed on one or more occasions to 10 C (50 F) air in the Metabolic Chamber for periods of 2–4 hr. A minimal amount of clothing was worn: the males wore shorts and the females wore halters and shorts. Air movement was routinely less than 50 ft/min and relative humidity 50% or less. Body fatness among the subjects ranged from 13 to 45% of body weight. The metabolic response to cold determined from Vo2 and Vco2 was significantly and inversely related to per cent body fat according to the regression equation: kcal/(m2·hr) = 65.2 – 0.520 (% fat) ± 0.115. Total body insulation after 2 hr of exposure was significantly and directly related to per cent body fat and inversely related to the metabolic response. Despite these significant relationships, wide individual differences were observed in the metabolic response to cold between pairs of subjects of like age, previous history of cold exposure, and body fatness.