[Physical activity and health].

in younger adults (Kohrt et al. 1991). The interrelationships of age, \i02max, and training status are evident when the loss inVO,max with age is compared for active and sedentary individuals (Figure 3-5). When the cardiorespiratory responses of an older adult are coinpared with those of a young or middleaged adult at the same absolute submaximal rate of work, stroke volume for an older person is generally lower and heart rate is higher from the attempt to maintain cardiac output. Because this attempt is generally insufficient, the A-+0, difference must increase to provide the same submaximal oxygen uptake (Raven and Mitchell 1980; Thompson and Dorsey 1986). Some researchers have shown, however, that cardiac output can be maintained at both submaximal and maximal rates of work through a higher stroke volume in older adults (Rodeheffer et al. 1984). The deterioration in physiological function normally associated with aging is, in fact, caused by a combination of reduced physical activity and the aging process itself. By maintaining an active lifestyle, or by increasing levels of physical activity if previously sedentary, older persons can maintain relatively high levels of cardiovascular and metabolic function, including irO,max (Kohrt et al. 199 1)) and of skeletal muscle function (Rogers and Evans 1993). For example, Fiatarone and colleagues (1994) found an increase of 113 percent in the strength of elderly men and women (mean age of 87.1 years) following a lo-week training program of progressive resistance exercise. Cross-sectional thigh muscle area was increased, as was stair-climbing power, gait velocity, and level of spontaneous activity. Increasing endurance and strength in the elderly contributes to their ability to live independently.