AIM: We investigated the cardiorespiratory response during acute sprint interval exercise (SIE; 4 x 30 sec maximal efforts, each separated by 4 min recovery) vs. continuous endurance exercise (CEE; 30 min) at 70% VO2max. METHODS: Oxygen consumption (VO2) and heart rate were measured in 8 males (age: 23±2.3 y, height: 181±6.4 cm, body mass: 78±8.6 kg, VO2max: 52±3.1 ml/kg·min, mean±SD). Pre-exercise diet was controlled. RESULTS AND CONCLUSION: Total VO2 was greater with CEE vs. SIE (87.6±13.1 vs. 35.1±4.4 L O2) with small differences (P=0.06) in average heart rates (CEE: 157±10 bpm vs. SIE: 149±6 bpm) and peak heart rates (CEE: 166±10 vs. SIE: 173±6; P=0.14). VO2 increased during the sprint bouts (53-72% of VO2max) and attained near maximal values (84-96%) in the immediate recovery period (within 20 sec). Thereafter a rapid decrease occurred so that at 2 min of recovery VO2 was ~1.5 L/min (~38% VO2max). During the remaining 2 min of recovery VO2 declined more slowly to ~1.3 L/min or ~33% of VO2max. Similar heart rate responses with CEE and SIE and a greater VO2 during SIE suggest increased muscle oxygen extraction with SIE, which might explain the greater peripheral adaptations, observed previously with sprint vs. continuous training. The potential value of shorter recovery durations to SIE needs to be examined.
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