Blood volume expansion following supramaximal exercise : occurrence and contribution to maximal oxygen uptake

Abstract: Previously published research using various types of exercise has shown that central hemodynamic factors such as blood volume (BV) and maximal cardiac output (Qmax) are of large importance in the mediation of improvements in VO2max. Whether this is true for adaptations induced by sprint-interval training (SIT) is unclear. Three experimental studies were carried out investigating the occurrence and contribution of hypervolemia to SIT-induced improvements in VO2max. Forty-eight study participants performed the interventions. Significant increases in BV and Qmax were observed after the 6-week training interventions in conjunction with the expected increases in VO2max (Paper Ⅰ and Ⅱ). The hypervolemic response was shown not only to be associated with the increase in VO2max but also to be the primary mediator of it, as demonstrated by the elimination of the exercise-induced increases in VO2max when BV was normalized to pre-intervention levels by phlebotomy. This demonstrates that central adaptations are paramount for the SIT-induced increase in VO2max. In addition, systemic oxygen extraction increased as a consequence of decreased venous oxygen content during maximal exercise (Paper Ⅱ). This suggests that both peripheral and central factors are responsible for the adaptations in VO2max observed with SIT and refutes previous theories proposing that the increase in VO2max was mediated primarily by peripheral adaptations. Metabolic and intravascular perturbation has been proposed as an important stimuli for exercise adaptation. Since SIT is one of the most intense forms of exercise available the immediate effects after SIT are interesting in order to understand how such small amounts of exercise can lead to cardiovascular adaptations usually associated with more prolonged types of exercise. Acute effects of one session of SIT caused pronounced disturbance of the intravascular milieu and perturbations of the muscle metabolism. The variable that correlated best with changes in plasma and muscle volume was glucose-6-phosphate (Paper Ⅲ). Similarly, plasma osmolality and plasma concentration of arginine and citrulline was shown to be the best predictors of improvements in VO2max after a training intervention of 6-weeks (Paper Ⅳ). Overall, the present work demonstrates that brief supramaximal exercise leads to improvements in VO2max and that these improvements are mediated mainly by central adaptations. Peripheral adaptations occur concurrently but cannot alone explain the improvements in VO2max, as previously hypothesized. The data presented show that both central and peripheral adaptations are involved in the improvement of VO2max after an SIT intervention.