Effects of Exercise Training Intensity on Cardiorespiratory Fitness and Cardiovascular Disease Risk Factors in Young and Early Middle-Aged Adults at Moderate Risk for Cardiovascular Disease

Abstract

Introduction: Exercise training is an effective strategy for improving cardiovascular disease (CVD) risk factors. However, it is unclear whether high-intensity training is more effective than moderate-intensity training in improving maximal oxygen uptake (VO2max) and insulin resistance, when weekly exercise volume is matched. Aim: To determine the effect of exercise training intensity when exercise volume is controlled on VO2max and insulin resistance. Secondary outcomes include traditional (blood pressure, waist circumference, blood lipids) and non-traditional (C-reactive protein) CVD risk factors. Methods: Sedentary adults at moderate risk of CVD were randomised into one of four groups: high volume moderate intensity (HVMI, n = 15), high volume high intensity (HVHI, n = 14), low volume moderate intensity (LVMI, n = 15) and sedentary control (n = 13). Only HVMI, HVHI and controls were examined in this thesis. Exercise groups completed 12 weeks of training at a target intensity of either 50% (HVMI) or 80% of VO2 reserve (HVHI), with the target volume of exercise prescribed relative to body mass (16 kcal·kg-1·week-1) split evenly over four weekly exercise sessions. Linear regression models, which controlled for age and gender, were used to determine the effect of exercise training intensity on the mean change in primary and secondary outcomes over 12 weeks. Results: The mean increase in VO2max was significantly greater in HVMI compared to HVHI (p = 0.042) and control (p = 0.041). The change in insulin resistance and secondary outcomes were not different among groups (p0.8). Conclusions: Over 12 weeks, moderate intensity exercise training was more beneficial than high intensity training in improving VO2max; however, no other significant intensity-related effects were observed for any other CVD risk factors.