The FITT Principle in Individuals with Type 2 Diabetes: From Cellular Adaptations to Individualized Exercise Prescription

Diabetes mellitus is a complex disease that affects millions of people worldwide. Type 2 diabetes (T2DM) arises from a combination of genetic susceptibility and environmental factors, including physical inactivity and poor nutritional habits. Accumulating evidence suggests that the majority of T2DM cases can be prevented through diet, physical activity, and exercise modification. Acute exercise bouts improve glucose homeostasis by increasing skeletal muscle glucose uptake through insulin-dependent and non-insulin dependent pathways; whereas, chronic exercise training induces alterations in genes’ expression, promoting mitochondrial biogenesis, glucose transporters (GLUT4) expression and protein enhancements, and fiber type transformation. However, individuals with T2DM show a low participation and poor adherence to exercise training. Alterations in metabolic, vascular and neural function induced by T2DM may impede skeletal muscle blood-flow during exercise, contributing to exercise intolerance. Thus, appropriate exercise programs that will improve glycemic control and will be attractive and effective for the individual with diabetes are still needed. The purpose of this article is (i) to present cellular mechanisms through which exercise can improve glycemic control, (ii) to describe the exercise prescription characteristics (frequency, intensity, time, type; FITT) required to achieve optimal benefits in T2DM, and (iii) to highlight the pathophysiological alterations induced by T2DM and obesity that should be considered when designing an exercise program. Genetic predisposition, diabetes/obesity phenotypes, oxidative stress, brain insulin sensitivity, perceived exertion, and initial fitness levels or training experience influence the inter-individual variability in exercise responsiveness. Thus, exercise is prescription should be individualized in order to achieve maximal benefits and high adherence.