Effects of Short-Term High versus Continuous Moderate Intensity Training on Insulin Resistance in Overweight and Obese Adults: A Randomized Controlled Trial

In long-term exercise training studies ( > 6 weeks), improvements in insulin resistance (IR) are amplified by decreased body fat and/or increased cardio-respiratory fitness. This presents a challenge in studying the independent effects of exercise training. Our study purpose was to determine the effects of short-term continuous moderate intensity training (CMIT) and high intensity interval training (HIIT) on IR in overweight/obese adults. Participants were stratified into insulin sensitive (IS) and IR groups, and randomized into non-exercise control (CNT), CMIT and HIIT sub-groups that underwent baseline and post testing. Exercise sessions were 18-24 minutes for 10 consecutive days. The CMIT sub-group continuously cycled at 60-70% of peak oxygen consumption (VȮ2peak) while the HIIT sub-group performed 60s of cycling at 90-100% VȮ2peak interspersed with 30 seconds of rest. Ninety-five participants (mean age and BMI 23.9 + 3.9 years and 32.1 + 5.0 kg/m ² ) were enrolled into the study. Of these, 63% were IS and 37% had IR. CMIT or HIIT did not result in statistically significant improvements in IR. However, the reduction (32.4%) in IR observed with HIIT may be of clinical relevance. Cohen’s (d) effect size (ES) for HIIT on IR was large (ES: d =-0.9; 95% CI:-1.7,-0.1) while that of CMIT was unclear (ES: d =-0.2; 95% CI:-1.0, 0.6). In the current study, CMIT or HIIT did not result in statistically significant improvements in insulin resistance. Future large-scale studies to clarify and confirm our findings are warranted.