Short-Term Sprint Interval Training Increases Maximal Oxygen Uptake Without Changing Maximal Cardiac Output

Abstract

Traditional moderate intensity continuous training increases maximal oxygen uptake (VO2max). This effect is primarily attributed to an increased maximal cardiac output (Qmax), as predicted by the Fick principle. Sprint interval training (SIT) increases VO2max similar to MICT, often despite a lower training volume, but the effect on Qmax is unclear. PURPOSE: To determine the effect of 6 sessions of SIT over 2 wk on VO2max, Qmax and exercise performance in healthy, untrained adults [n=12 (9 females); 21±2 y; mean±SD]. METHODS: Training was performed on a cycle ergometer and involved a 2-min warm-up (50 W), 3 x 20-s ‘all-out’ bouts interspersed with 2-min of recovery (50 W), and a 3-min cool-down (50 W). VO2max was determined using a ramp test to exhaustion. Qmax was subsequently determined using inert gas rebreathing (Innocor) over a 2-min period of exercise performed at 90% of the peak work rate attained during the VO2max test. Pilot testing confirmed this protocol elicited VO2max over the 2-min period of Qmax measurement. The performance test was a 2 kJ/kg body weight cycling time trial. All measurements were performed twice at baseline, and reproducibility determined as a coefficient of variation (CV). The CV for VO2max, Qmax and time trial performance was 5.8, 4.7 and 4.2%, respectively. Pre- and post-training measurements were compared using a paired t-test. RESULTS: VO2max increased after SIT from 37.0±7.3 to 40.7±8.3 ml/kg/min (p<0.001), but Qmax was unchanged (17.2±3.8 vs 17.7±4.6 L/min; p>0.05). Exercise performance improved after SIT from 1040±247 to 938±238 s (p<0.001). Absolute VO2max was positively correlated with Qmax (r2 = 0.86, p < 0.001). CONCLUSION: Six sessions of SIT increased VO2max without changing Qmax in previously untrained individuals. These data support previous suggestions that the early increase in VO2max after SIT may be due mainly to peripheral responses (i.e., enhanced oxygen extraction by skeletal muscle), rather than a central change in blood oxygen delivery. Supported by NSERC