PURPOSE: To investigate the effects and time course of endurance training on the regulation of heart rate (HR), arterial pressure (AP), norepinephrine (NE), and plasma volume (PV) during orthostatic stress in healthy elderly men. METHODS: Thirty-one healthy men (65 to 75 yr) were randomly allocated into endurance training (N = 20, EX) and control (N = 11, CON) groups. The EX group cycled 3 d/wk for 30 min at 70% VO2peak for 12 wk x VO2peak was determined on an electronically braked cycle ergometer, before training and after 4, 8, and 12 wk of endurance training. The immediate (initial 30 s), early steady-state (1 min), and prolonged (5, 10, 15 min) beat-by-beat HR and AP responses during 90 degrees head-up tilt (HUT) were measured at least 3 d after each VO2peak test. Spontaneous baroreflex slopes were determined by application of linear regression to sequences of at least three cardiac cycles in which systolic blood pressure (SBP) and R-R interval changed in the same direction. Venous blood was collected during 90 degrees HUT and analyzed for changes in plasma NE concentrations, as well as hematocrit and hemoglobin to determine changes in PV. RESULTS: Endurance training significantly (p < 0.01) increased VO2peak (mL/kg/min) in EX by 10 +/- 2%. The immediate, early steady-state, and prolonged HR and AP responses and spontaneous baroreflex slopes during 90 degrees HUT were not significantly different (p > 0.05) between EX and CON groups before or after 4, 8, or 12 wk of endurance training. No significant differences (p > 0.05) were observed between EX and CON groups for peak changes in PV during orthostasis before (-15.0 +/- 1.4% versus -11.9 +/- 1.3%) or after 4 (-12.2 +/- 1.0% versus -12.7 +/- 1.4%), 8 (-13.7 +/- 1.2% versus -12.4 +/- 0.7%), and 12 wk (-10.8 +/- 1.6% versus -10.6 +/- 0.6%) of endurance training, suggesting a similar stimulus presented by 90 degrees HUT in both groups. Peak changes in NE concentrations during HUT were similar (p > 0.05) between EX and CON groups before (119 +/- 23 pg/mL versus 191 +/- 36 pg/mL) and after 4 (139 +/- 29 pg/mL versus 146 +/- 25 pg/mL), 8 (114 +/- 32 pg/mL versus 182 +/- 41 pg/mL), and 12 wk (143 +/- 35 pg/mL versus 206 +/- 42 pg/mL) of endurance training. CONCLUSIONS: These data indicate that in healthy elderly men, improvements in VO2peak can occur without compromising the regulation of HR, AP, NE, and PV during orthostatic stress.

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