The purpose of this study was to compare the effectiveness of either continuous moderate intensity exercise training (CMIET) alone versus CMIET combined with a single weekly bout of high intensity interval training (HIIT) on cardiorespiratory fitness. Twenty nine sedentary participants (36.3 +/- 6.9 yrs) at moderate risk of cardiovascular disease were recruited for 12 weeks of exercise training on a treadmill and cycle ergometer. Participants were randomised into three groups: CMIET+HIIT (n = 7; 8 to 12 x 60 sec at 100% VO2max, 150 sec active recovery), CMIET (n = 6; 30 min at 45 to 60% oxygen consumption reserve (VO2R)) and a sedentary control group (n = 7). Participants in the CMIET+HIIT group performed a single weekly bout of HIIT and four weekly sessions of CMIET, whilst the CMIET group performed five weekly CMIET sessions. Probabilistic magnitude-based inferences were determined to assess the likelihood that the true value of the effect represents substantial change. Relative VO2max increased by 10.1% (benefit possible relative to control) in in the CMIET+HIIT group (32.7 +/- 9.2 to 36.0 +/- 11.5 mL/kg/min) and 3.9% (benefit possible relative to control) in the CMIET group (33.2 +/- 4.0 to 34.5 +/- 6.1 mL/kg/min), whilst there was a 5.7% decrease in the control group (30.0 +/- 4.6 to 28.3 +/- 6.5 mL/kg/min). It was 'unclear' if a clinically significant difference existed between the effect of CMIET+HIIT and CMIET on the change in VO2max. Both exercising groups showed clinically meaningful improvements in VO2max. Nevertheless, it remains 'unclear' whether one type of exercise training regimen elicits a superior improvement in cardiorespiratory fitness relative to its counterpart.

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