"Weighing" the effects of exercise and intrinsic aerobic capacity: are there beneficial effects independent of changes in weight?

It has been known for centuries that regularly performed exercise has beneficial effects on metabolic health. Owing to its central role in locomotion and the fact that it accounts for a large majority of whole-body glucose disposal and fatty acid oxidation, the effects of exercise on skeletal muscle has been a central focus in exercise physiology research. With this being said it is becoming increasingly well recognized that both adipose tissue and liver metabolism are robustly modified by exercise, especially in conditions of obesity and insulin resistance. One of the difficult questions to address is if the effects of exercise are direct or occur secondary to exercise-induced weight loss. The purpose of this review is to highlight recent work that has attempted to tease out the protective effects of exercise, or intrinsic aerobic capacity, against metabolic and inflammatory challenges as it relates to the treatment and prevention of obesity and insulin resistance. Recent studies reporting improvements in liver and adipose tissue insulin action following a single bout of exercise will also be discussed. The research highlighted in this review sheds new insight into protective, anti-inflammatory effects of exercise that occur largely independent of changes in adiposity and body weight.