The effect of continuous moderate intensity exercise training combined with high intensity interval training on cardiovascular disease risk factors

Abstract

Cardiovascular diseases (CVD) and type 2 diabetes are a major health and economic burden on society and without intervention, incidence will continue to increase. High intensity interval training (HIIT) is emerging as a time efficient strategy for improving risk factors of CVD and type 2 diabetes; however, there is a lack of research on HIIT in sedentary, at-risk individuals. Whilst HIIT has shown superior improvement in CVD risk factors, when compared with continuous moderate intensity exercise training (CMIET), it may be unrealistic to exclusively adopt this form of training as a lifestyle change. PURPOSE: The purpose of this study was to compare how 12 weeks of HIIT and CMIET affected cardiorespiratory fitness (VO2max), insulin sensitivity and other risk factors for CVD, in sedentary individuals at moderate risk of CVD. METHODS: Twenty nine sedentary subjects at moderate risk of CVD were recruited for 12 weeks of exercise training. Subjects were randomised into three groups: HIIT (n=9; 8-12 x 60 sec at 100% VO2max, 150 sec active recovery), CMIET (n=10; 30 min at 45-60% oxygen consumption reserve (VO2R)) and a sedentary control group (n=10). Participants in the HIIT group performed a single weekly bout of HIIT and four weekly sessions of CMIET, whilst the CMIET group performed five weekly CMIET sessions. Cardiorespiratory fitness, insulin sensitivity (HOMA model), blood lipids, body composition and quality of life were measured pre and post intervention. Probabilistic magnitude-based inferences were determined to assess the likelihood that the true value of the effect represented substantial change. RESULTS: Relative VO2max increased by 10.1% in in the HIIT group (32.7 ± 9.2 to 36.0 ± 11.5 mL·kg-1·min-1) and 3.9% in the CMIET group (33.2 ± 4.0 to 34.5 ± 6.1 mL·kg-1·min-1), whilst there was a 5.7% decrease in the control group (30.0 ± 4.6 to 28.3 ± 6.5 mL·kg-1·min-1). It was ‘unclear’ if a clinically significant difference existed between the HIIT and CMIET groups. There was a decrease in insulin sensitivity for both exercising groups (HIIT: 101 ± 27.3 to 90.3 ± 29.0%; CMIET: 95.6 ± 42.6 to 84.1 ± 25.6%), with a ‘possibly trivial’ clinical inference between groups. CONCLUSION: Both exercising groups showed clinically meaningful improvements in VO2max, body composition (hip and waist circumference), systolic and diastolic blood pressure and total and LDL cholesterol. However, it remains ‘unclear’ whether one type of exercise training regimen elicits a superior CVD risk factor reduction relative to its counterpart.