Cardiovascular and peak ??VO2 responses to supine exercise: effects of age and training status

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Abstract
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 (˙VO2) 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˙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 had lower (P < 0.05) peak ˙VO2 (ml·min-1) and peak heart rate responses during supine cycling compared with treadmill exercise. Additionally, the age-related reduction in peak ˙VO2 (≈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(˙VO2) 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 ˙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 reduced peak ˙VO2.