Twelve weeks of sprint interval training increases maximal cardiac output

Abstract

The improved maximal oxygen uptake (V̇O2max) after traditional moderate intensity continuous training (MICT) is generally attributed to increased maximal cardiac output (Q̇max). Sprint interval training (SIT) increases V̇O2max similar to MICT despite a lower training volume, but the effect on Q̇max is unclear. Purpose: To determine the effect of ~30 sessions of SIT over 12 weeks on Q̇max and its association with the change in V̇O2max. Methods: 15 healthy untrained adults [6 males, 9 females; 21±2 y (mean±SD)] performed a SIT protocol involving 3x20-s ‘all-out’ cycling bouts (581±221 W) within a 10-min period. V̇O2max was determined using a ramp test to exhaustion. Q̇max was determined using inert gas rebreathing over a 2-min period at a workload that elicited V̇O2max during the measurement period. All variables were assessed twice at baseline following familiarization and again after 2, 6 and 12 weeks of SIT. Reproducibility of V̇O2max and Q̇max, determined using the baseline measures and expressed as a coefficient of variation, was 5.8 and 4.7%, respectively. Results: V̇O2max increased from 2.65±0.85 at baseline to 2.85±9.6, 3.03±1.1 and 3.18±1.1 L/min after 2, 6 and 12 weeks, respectively (p<0.001 for all). Q̇max increased from 17.2±3.8 at baseline to 18.1±4.6 L/min after 12 weeks (p=0.04) but was not different after 2 (17.2±4.2; p=0.96) or 6 weeks (17.9±4.4; p=0.14). The changes in V̇O2max and Q̇max from baseline to 12 weeks were positively correlated (r2=0.46, p=0.005). Secondary exploratory analyses revealed that males increased Q̇max after 6 and 12 weeks, but there was no change in females. Conclusion: The increase in V̇O2max after 12 weeks of SIT is associated with an increase in Q̇max, and there may be sex-specific differences in this regard.