The succession of on-transient phases that induce a repetition of metabolic changes is a possible mechanism responsible for the greater response to IT. The objective of this study was to quantify fluctuations during intermittent exercise characterized by the same work:rest ratio, but different durations and identify which duration leads to the greatest fluctuations. Ten participants (24±5 years; VO 2max : 42±7 mL·min-1·kg-1) performed: 1) an incremental test to exhaustion to determine peak work rate (WRpeak) and oxygen uptake (VO2max), 2), and three 1-hour 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). VO2 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 VO2 differences (ΣΔVO2) and the oxygen fluctuation index (OFI) were both greater in the 60s:60s condition (ΣΔVO2: +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). VO2 fluctuations analysis was successful in identifying the intermittent condition associated with the greatest disturbances: the 60s:60s duty-cycle induces more VO2 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 VO2 fluctuations.