To study the effects of cardiovascular fitness on hemodynamic responses to exercise during β-adrenergic blockade (BAB), submaximal [60% of maximum O2 uptake (V̇(O2(max)))] and maximal treadmill exercise data were collected in 11 trained (T, V̇(O2(max)) 63.3 ml·kg-1·min-1, 26.8 yr) and 11 untrained (UT, V̇(O2(max)) 44.5 ml·kg-1·min-1, 25.0 yr) male subjects. Subjects completed two maximal control tests followed by a randomized, double-blind series of maximal tests after 1-wk treatments with placebo (PLAC), propranolol (PROP, 160 mg/day, β1- and β2-blockade), and atenolol (ATEN, 100 mg/day, β1-blockade). Treatments were separated by 1-wk washout periods. At 60% of control V̇(O2(max)) T and UT subjects experienced no reductions in O2 uptake (V̇(O2)) with either drug. Submaximal heart rate (HR, beats/min) was 134.8 PLAC, 107.0 PROP, 107.9 ATEN (P < 0.05 both drugs vs. PLAC) in T subjects and 141.1 PLAC, 106.1 PROP, and 105.0 ATEN (P < 0.05 both drugs vs. PLAC) in UT subjects. Cardiac output (1/min) for T was 17.3 PLAC, 16.9 PROP, 16.5 ATEN (P < 0.05 ATEN vs. PLAC in T only) and for UT it was 12.2 (PLAC), 11.7 (PROP), 11.5 (ATEN) (P < 0.05 both drugs vs. PLAC in UT). Stroke volume increased from 129.8 ml (PLAC) to 158.6 (PROP) and 156.2 (ATEN) T (P < 0.05 both drugs vs. PLAC) and from 86.8 (PLAC) to 110.0 (PROP) and 109.8 (ATEN) (P < 0.05 both drugs vs. PLAC) in UT. The increases in stroke volume (SV) were similar in both groups. Maximum heart rate (HR(max)) fell from 184.2 (PLAC) to 142.7 (PROP) and 149.5 (ATEN) in T subjects (P < 0.05 both drugs vs. PLAC, ATEn > PROP), and 196.8 (PLAC) to 144.1 (PROP) and 148.9 (ATEN) in UT subjects (P < 0.05 both drugs vs. PLAC). V̇(O2(max)) (ml·kg-1·min-1) was 63.3 PLAC, 56.2 PROP, 59.3 ATEN in T subjects (P < 0.05 both drugs vs. PLAC, ATEN > PROP) and 44.5 PLAC, 41.6 PROP, 42.6 ATEN in UT subjects (P < 0.05 both drugs vs. PLAC). The drop in V̇(O2(max)) was greater in T than UT subjects during PROP. These data indicate that 1) T as well as UT subjects experience large increases in exercise SV during BAB and 2) the increases in SV suggest that factors other than central hemodynamics may cause the somewhat larger reductions in V̇(O2(max)) in T subjects during exercise with BAB.
ASJC Scopus subject areas
- Physiology (medical)