Effect of work: rest cycle duration on VO2 fluctuations during intermittent exercise

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 fluctuations during intermittent exercise characterised by the same work:rest ratio, but different durations and identify which duration leads to the greatest fluctuations. Ten participants (24 +/- 5years; : 42 +/- 7 mL min(-1)kg(-1)) performed (1) an incremental test to exhaustion to determine peak work rate (WRpeak) and oxygen uptake (), (2), and three 1 h intermittent exercises alternating work period at 70% WRpeak with passive recovery period of different 1:1 work:recovery duty cycles (30s:30s, 60s:60s, 120s:120s). 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 differences (sigma) and the oxygen fluctuation index (OFI) were both greater in the 60s:60s condition (sigma: +38%+/- 13% and +19%+/- 18% vs. 120s:120s and 30s:30s, P<0.05; OFI: +41%+/- 29% and +67%+/- 62% vs. 120s:120s and 30:30s, P<0.05). fluctuation analysis was successful in identifying the intermittent condition associated with the greatest disturbances: the 60s:60s duty cycle induces more 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 fluctuations.