Increased maximal oxygen uptake after sprint-interval training is mediated by central haemodynamic factors as...

There is a lack of knowledge regarding the contribution of central and peripheral factors to the increases in VO_2max following sprint-interval training (SIT). This study investigated the importance of maximal cardiac output (Q_max ) in relation to VO_2max improvements following SIT and the relative importance of the hypervolemic response on Q_max and VO_2max . We also investigated whether systemic O₂ extraction increased with SIT as has been previously suggested. Healthy men and women (n = 9) performed 6 weeks of SIT. State-of-the-art measurements: right heart catheterization, carbon monoxide rebreathing and respiratory gas exchange analysis were used to assess Q_max , arterial O₂ content (c_a O₂ ), mixed venous O₂ content (c_v O₂ ), blood volume (BV) and VO_2max before and after the intervention. In order to assess the relative contribution of the hypervolemic response to the increases in VO_2max , BV was re-established to pre-training levels by phlebotomy. Following the intervention, VO_2max , BV and Q_max increased by 11% (P < 0.001), 5.4% (P = 0.013) and 8.8% (P = 0.004), respectively. c_v O₂ decreased by 12.4% (P = 0.011) and systemic O₂ extraction increased by 4.0% (P = 0.009) during the same period, both variables were unaffected by phlebotomy (P = 0.589 and P = 0.548, respectively). After phlebotomy, VO_2max and Q_max reverted back to pre-intervention values (P = 0.064 and P = 0.838, respectively) and were significantly lower compared with post-intervention (P = 0.016 and P = 0.018, respectively). The decline in VO_2max after phlebotomy was linear to the amount of blood removed (P = 0.007, R = -0.82). The causal relationship between BV, Q_max and VO_2max shows that the hypervolemic response is a key mediator of the increases in VO_2max following SIT. KEY POINTS: Sprint-interval training (SIT) is an exercise model involving supramaximal bouts of exercise interspersed with periods of rest known for its efficiency in improving maximal oxygen uptake (VO_2max ). In contrast to the commonly accepted view where central haemodynamic adaptations are considered to be the key mediators of increases in VO_2max there have been propositions highlighting peripheral adaptations as the main mediators in the context of SIT-induced changes in VO_2max . By combining right heart catheterization, carbon monoxide rebreathing and phlebotomy, this study shows that increases in maximal cardiac output due to the expansion of the total blood volume is a major explanatory factor for the improvement in VO_2max following SIT, with a smaller contribution from improved systemic oxygen extraction. The present work not only clarifies a controversy in the field by using state-of-the-art methods, but also encourages future research to investigate regulatory mechanisms that could explain how SIT can lead to improvements in VO_2max and maximal cardiac output similar to those that have previously been reported for traditional endurance exercise.