Heart rate and sweat rate responses associated with exercise-induced hypervolemia

The purpose of this study was to determine the relationships between the plasma volume (PV) expansion accompanying exercise training and the associated changes in heart rate (HR) and sweat rate (SR) during sub-maximal and maximal exercise. Eight male subjects (21 +/- 1 yr) rode a cycle ergometer 2 h/d for 8 consecutive days at 65% maximal oxygen uptake (VO2max). Average HR and SR were measured each day during exercise, and PV (T-1824) was measured prior to, on day 4, and the day following exercise training. The VO2max and maximal HR (HRmax) were measured before and after the 8-d exercise period. Following exercise training, VO2max increased by 8.3% (P less than 0.05), HRmax decreased by 4.1% (P less than 0.05), and PV increased by 430 ml (+ 12.2%, P less than 0.05). During the 2-h ergometer exercise, mean SR increased from 0.83 1 . h-1 on day 1 to 0.97 1 . h-1 on day 8 (P less than 0.05) while mean HR decreased from 169 beats per min (bpm) on day 1 to 148 bpm on day 8 (P less than 0.05). The percent change (% delta) in PV was correlated with % delta SR (r = 0.93, P less than 0.05), % delta HR at 65% VO2max (r = -0.89, P less than 0.05), and % delta HRmax (r = -0.82, P less than 0.05). The data indicated that plasma volume expansion may be necessary for the cardiovascular and thermoregulatory adaptations accompanying chronic exercise.