Cardiovascular and peak V̇O₂ responses to supine exercise: Effects of age and training status

Although stroke volume during exercise is affected by aging and posture, few studies have carefully examined the heart rate, blood pressure, and peak oxygen uptake (V̇O₂) responses of older subjects to supine exercise. The present study examined these responses during graded supine cycling in younger (21-30 yr) and older (51-62 yr) untrained (Treadmill V̇O(2max) = 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 had lower (P < 0.05) peak V̇O₂ (ml · min^-1) and peak heart rate responses during supine cycling compared with treadmill exercise. Additionally, the age-related reduction in peak V̇O₂ (~20-30%) was similar for supine compared with treadmill testing, even when normalized to fat-free leg volume and fat-free mass, respectively. However, at given absolute intensities (V̇O₂) of supine exercise, heart rates were 10-15 beats · min^-1 less (P < 0.05) in both older groups. Across relative supine work intensities (% of peak), systolic pressure increased most rapidly in the younger trained and older untrained groups. These findings suggest that the effects of aging on peak V̇O₂ 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 reduced peak V̇O₂.