Background

Many high-profile athletes participate across a wide range of sports with type 1 diabetes. Team Type 1 encourages and supports those with type 1 diabetes to participate in physical activity, with professional cycling’s Team Novo Nordisk composed entirely of individuals with type 1 diabetes. Type 1 diabetes is likely to present early in an athlete’s career, a time when athletes may present with fatigue due to increased training loads. All physicians need to distinguish between possible causes of fatigue in these athletes.

Type 1 diabetes is an autoimmune condition with T-cell-mediated destruction of the pancreatic β cells of the islets of Langerhans, resulting in failure to produce sufficient insulin. The clinical outcome is an inability to adequately control glucose metabolism. Effective glucose metabolism is crucial in long-duration and high-intensity exercise. Self-administered exogenous insulin is required as a treatment to manage blood glucose.

The physiological response to exercise is a progressive decrease in insulin and increase in the pancreatic α-cell-derived antagonist hormone glucagon, while exercise also increases insulin sensitivity (increased ‘sensitivity’ means that for a given dose, there is a more pronounced effect—insulin does its job ‘better’). In addition, there is an exercise-induced rise in sympathoadrenal hormones …