CARDIOVASCULAR AND PEAK VO2 RESPONSES TO SUPINE EXERCISE - EFFECTS OFAGE AND TRAINING STATUS

Although stroke volume during exercise is affected by aging and postur e, few studies have carefully examined the heart rate, blood pressure, and peak oxygen uptake (VO2) responses of older subjects to supine ex ercise. The present study examined these responses during graded supin e cycling in younger (21-30 yr) and older (51-62 yr) untrained (Treadm ill VO2max = 47.0 vs 32.3 ml . kg(-1). min(-1)) and endurance-trained (66.3 vs 52.7 ml . kg(-1). min(-1)) men (N = 6/group). All subjects ha d lower (P < 0.05) peak VO2 (ml . min(-1)) and peak heart rate respons es during supine cycling compared with treadmill exercise. Additionall y, the age-related reduction in peak VO2 (similar to 20-30%) was simil ar for supine compared with treadmill testing, even when normalized to fat-free leg volume and fat-free mass, respectively. However, at give n absolute intensities (VO2) of supine exercise, heart rates were 10-1 5 beats . min(-1) less (P < 0.05) in both older groups. Across relativ e supine work intensities (% of peak), systolic pressure increased mos t rapidly in the younger trained and older untrained groups. These fin dings suggest that the effects of aging on peak VO2 are similar during treadmill and supine exercise in both endurance-trained and untrained men. These data also indicate that the heart rate response to supine exercise is attenuated in healthy older men and contributes to their r educed peak VO2.