Cardiorespiratory efficiency at submaximal work in young and middle-aged women

Seventeen middle-aged women and 26 younger women were studied while walking at 3 mph and a 5% grade on a motorized treadmill. This was submaximal work for all subjects and is equivalent to the intensity of everyday activity. The middle-aged women had a significantly greater oxygen uptake, ventilatory equivalent, and heart rate, suggesting a relative cardiorespiratory inefficiency at this submaximal work intensity. This phenomenon is most likely a function of body size, however, since dividing the submaximal oxygen uptake by body weight rendered the mean difference between the two groups statistically insignificant. The age-associated reduction in cardiorespiratory efficiency at submaximal exercise is thus due primarily to weight gain rather than to actual systems degeneration. Maximal oxygen uptake, that associated with maximal physical effort, was significantly reduced in the older subjects, and this is probably due to a combination of previous life-style habits and aging.