Does endurance training affect orthostatic responses in healthy elderly men?

Purpose: To investigate the effects and time course of endurance training o n 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 (65-75 yr) were randomly allocated int o endurance training (N = 20 EX) and control (N = 11, CON) groups. The EX g roup cycled 3 d.wk(-1) for 30 min at 70% V(over dot)O-2peak for 12 wk.V(ove r dot)O-2peak was determined on an electronically braked cycle ergometer, b efore training and after 4. 8, and 12 wk of endurance training. The immedia te (initial 30 s). early steady-state (I min), and prolonged (5, 10, 15 min ) beat-by-beat HR and AP responses during 90 degrees head-up tilt (HUT) wer e measured at least 3 d after each V(over dot)O-2peak test. Spontaneous bar oreflex slopes were determined by application of linear regression to seque nces of at least three cardiac cycles in which systolic blood pressure (SBP ) and R-R interval changed in the same direction. Venous blood was collecte d during 90 degrees HUT and analyzed for changes in plasma NE concentration s. as well as hematocrit and hemoglobin to determine changes in PV. Results : Endurance training significantly (P < 0.01) increased V(over dot)O-2peak (mL.kg(-1).min(-1)) 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 C ON groups before or after 4, 8, or 12 wk of endurance training. No signific ant differences (P > 0.05) were observed between EX and CON groups for peak changes in PV during orthostasis before (-15.0 +/- 1.4% vs - 11.9 +/- 1.3% ) or after 4 (-12.2 +/- 1.0% vs - 12.7 +/- 1.4%), 8 (-13.7 +/- 1.2% vs - 12 .4 +/- 0.7%), and 12 wk (-10.8 +/- 1.6% vs - 10.6 +/- 0.6%) of endurance tr aining, suggesting a similar stimulus presented by 90 degrees HUT in both g roups. Peak changes in NE concentrations during HUT were similar (P > 0.05) between EX and CON groups before (119 +/- 23 pg.mL(-1) vs 191 +/- 36 pg.mL (-1)) and after 4 (139 +/- 29 pg.mL(-1) vs 146 +/- 25 pg.mL(-1)), 8 (114 +/ - 32 pg.mL(-1) vs 182 +/- 41 pg.mL(-1)), and 12 wk (143 +/- 35 pg.mL(-1) vs 206 +/- 42 pg.mL(-1)) of endurance training. Conclusions: These data indic ate that in healthy elderly men, improvements in V(over dot)O-2peak can occ ur without compromising the regulation of HR. AP, NE, and PV during orthost atic stress.