Effect of work:rest cycle duration on [Formula: see text] fluctuations during intermittent exercise.

ABSTRACT

The succession of on-transient phases that induce a repetition of metabolic changes is a possible mechanism responsible for the greater response to intermittent training (IT). The objective of this study was to quantify [Formula see text] fluctuations during intermittent exercise characterised by the same workrest ratio, but different durations and identify which duration leads to the greatest fluctuations. Ten participants (24 ± 5 years; [Formula see text] 42 ± 7 mL·min-1·kg-1) performed (1) an incremental test to exhaustion to determine peak work rate (WRpeak) and oxygen uptake ([Formula see text]), (2), and three 1 h intermittent exercises alternating work period at 70% WRpeak with passive recovery period of different 11 workrecovery duty cycles (30 s30 s, 60 s60 s, 120 s120 s). [Formula see text] response analysis revealed differences in the fluctuations across the intermittent conditions despite an identical total energy expenditure. The sum of the cycle's nadir-to-peak [Formula see text] differences (ΣΔ[Formula see text]) and the oxygen fluctuation index (OFI) were both greater in the 60 s60 s condition (ΣΔ[Formula see text] +38% ± 13% and +19% ± 18% vs. 120 s120 s and 30 s30 s, P < 0.05; OFI +41% ± 29% and +67% ± 62% vs. 120 s120 s and 3030 s, P < 0.05). [Formula see text] fluctuation analysis was successful in identifying the intermittent condition associated with the greatest disturbances the 60 s60 s duty cycle induces more [Formula see text] fluctuations. The present findings also demonstrate that the selection of the duty cycle duration for submaximal intermittent exercise (70% of WRpeak) prescription is of interest to produce high [Formula see text] fluctuations.