Exercise Strategies for Targeting Abdominal, Visceral and Hepatic Fat

Abstract

There is increasing evidence that excess fat stored in the abdominal region, including visceral adipose tissue (VAT) and intrahepatic lipid (IHL) is strongly linked with cardiovascular and metabolic disease risk. This thesis comprised four studies designed to investigate the effect of exercise modality and dose on abdominal, visceral and hepatic fat. In study 1 (Chapter 2) a systematic review with meta-analysis was undertaken to examine the independent and synergistic effects of aerobic exercise training and progressive resistance training on the modulation of VAT. Results showed that aerobic exercise is an integral component for exercise therapy targeting VAT reduction. Study two (Chapter 3) employed a systematic review with meta-analysis to examine the effect of exercise training (aerobic and resistance) on IHL and alanine aminotransferase (ALT) levels in adults. Exercise in isolation reduced IHL, despite minimal weight loss, but there was no effect of exercise on ALT. A 12 week randomised controlled trial was undertaken to examine the efficacy of novel high intensity interval training (HIIT) compared with continuous moderate intensity training (MICT) or placebo control on abdominal adiposity, and other markers of cardiovascular risk, in inactive and overweight adults (Chapter 4). Whilst HIIT demonstrated a comparable gain in fitness to MICT, only MICT reduced abdominal adiposity in overweight adults. Finally, an 8-week randomised controlled trial was conducted to examine the efficacy of three commonly prescribed doses of aerobic exercise on IHL and VAT in inactive and obese adults (Chapter 5). All doses of aerobic exercise, regardless of volume and intensity, were effective in reducing IHL and VAT, compared with placebo, in the absence of clinically significant weight loss. These investigations provide new evidence demonstrating that aerobic exercise per se is an effective therapy for reducing abdominal adiposity (including VAT) and IHL in previously inactive overweight/obese adults. These benefits can occur in the absence of clinically meaningful weight loss, and with doses below the current recommended guidelines for obesity management.