Twelve weeks of sprint interval training increases peak cardiac output in previously untrained individuals

Abstract

Introduction

Sprint interval training (SIT), characterized by brief bouts of ‘supramaximal’ exercise interspersed with recovery periods, increases peak oxygen uptake (${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$) despite a low total exercise volume. Per the Fick principle, increased ${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$ is attributable to increased peak cardiac output (${\dot{{Q}}}_{\text{peak}}$) and/or peak arterio-venous oxygen difference (a-vO_2diff). There are limited and equivocal data regarding the physiological basis for SIT-induced increases in ${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$, with most studies lasting ≤ 6 weeks.

Purpose

To determine the effect of 12 weeks of SIT on ${\dot{{Q}}}_{\text{peak}}$, measured using inert gas rebreathing, and the relationship between changes in ${\dot{{Q}}}_{\text{peak}}$ and ${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$.

Methods

15 healthy untrained adults [6 males, 9 females; 21 ± 2 y (mean ± SD)] performed 28 ± 3 training sessions. Each session involved a 2-min warm-up at 50 W, 3 × 20-s ‘all-out’ cycling bouts (581 ± 221 W) interspersed with 2-min of recovery, and a 3-min cool-down at 50 W.

Results

Measurements performed before and after training showed that 12 weeks of SIT increased ${\dot{{Q}}}_{\text{peak}}$ (17.0 ± 3.7 vs 18.1 ± 4.6 L/min, p = 0.01, partial η² = 0.28) and ${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$ (2.63 ± 0.78 vs 3.18 ± 1.1 L/min, p < 0.01, partial η² = 0.58). The changes in these two variables were correlated (r² = 0.46, p < 0.01). Calculated peak a-vO_2diff also increased after training (154 ± 22 vs 174 ± 23 ml O₂/L; p < 0.01) and was correlated with the change in ${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$ (r² = 0.33, p = 0.03). Exploratory analyses revealed an interaction (p < 0.01) such that ${\dot{{Q}}}_{\text{peak}}$ increased in male (+ 10%, p < 0.01) but not female participants (+ 0.6%, p = 0.96), suggesting potential sex-specific differences.

Conclusion

Twelve weeks of SIT increased ${\dot{{Q}}}_{\text{peak}}$ by 6% in previously untrained participants and the change was correlated with the larger 21% increase in ${\dot{\text{V}}}{\text{O}}_{2{\text{peak}}}$.