Author(s): KONTRO, H., JENSEN, M., CASWELL, A., ABOODARDA, S.J., MACINNIS, M.J., Institution: UNIVERSITY OF CALGARY, Country: CANADA, Abstract-ID: 1434

INTRODUCTION:
An acute loss of blood volume is known to affect maximal aerobic capacity (V̇O2max), but its influence on prolonged submaximal exercise remains unclear. The objective of this study was to investigate the effect of acute phlebotomy on physiological responses to 60 minutes of submaximal exercise in the heavy domain and its subsequent impact on maximal exercise performance.
METHODS:
After baseline testing and a control trial, using a double-blind design, 17 moderately trained participants (5 female) underwent either phlebotomy (PHLE) to withdraw 7% of total blood volume, or a sham procedure (SHAM). Physiological, metabolic, perceptual, and neuromuscular responses were assessed during 60 minutes of submaximal exercise in the heavy domain (71 [6] % of V̇O2max) and during a subsequent severe intensity time-to-task failure trial.
RESULTS:
Phlebotomy significantly affected ventilation (+9 [11] % vs. control trial), ventilatory equivalent (+8 [7] %, heart rate (+6 [5] %), O2 pulse (-7 [6] %), and lactate (+34 [26] %) during submaximal exercise (p < 0.05). Maximal exercise was impaired, with a -30 [30] % reduction in time-to-task failure (P = 0.018) and a non-significant reduction in V̇O2max (-6 [8] %, P = 0.09). Submaximal V̇O2, RER, substrate oxidation, RPE, and neuromuscular fatigability were unaffected. The ventilatory and lactate responses in PHLE became progressively exacerbated during the 60-minute exercise bout with the greatest deviations compared with the control trial observed at the end of exercise.
CONCLUSION:
These findings highlight the role of circulating vascular volumes in mediating resilience against time-dependent disturbances in homeostasis during prolonged exercise. Blood volume and/or hemoglobin mass have a role in the regulation of ventilation and blood lactate even in steady state conditions.