Introduction: Pushing the Limits in Endurance Sports with T1D

The realm of endurance and ultra-endurance sports, once thought to be out of reach for those with type 1 diabetes (T1D), is now achievable for many. Countless inspiring stories have emerged of people with T1D conquering gruelling, sometimes extreme, endurance events lasting hours or even days. These achievements include World Tour cycling stage races 1, marathons and ultramarathons [2-5], Ironman competitions [6], multi-day hikes [7], and long-distance cross-country skiing [8, 9].

These accomplishments are a testament to human resilience and demonstrate what’s possible with careful planning, rigorous glucose monitoring, and strategic nutritional adjustments. Advances in diabetes technologies and management strategies have also significantly enabled these endurance feats among people with T1D [10].

For endurance sports athletes with T1D, managing blood glucose levels is an extra challenge compared to those without the condition. To optimise performance and recovery during key training sessions and competitions, they must contend with many factors, including hydration, electrolyte imbalances, glycogen depletion, gastrointestinal discomfort, disturbances in acid-base balance, and glucose management [11]. They must precisely navigate a complex interplay of variables to compete and win.

This chapter will explore how sports science principles might be applied to enhance training adaptations, performance, competition strategies, and recovery for endurance athletes living with T1D while managing glucose levels. By leveraging the latest research and insights and personalised glucose management, athletes living with T1D can push the boundaries of what is possible in sports. We will first discuss some key principles related to fuel metabolism and sports nutrition, followed by fluid management, diabetes technology, and other considerations such as safe weight management and travel.

 

1.      Sports Nutrition Principles and Their Relevance to the Athlete with T1D

Fuel Metabolism Changes During Exercise and Why Appropriate Fuelling Matters

Engaging in physical activity requires tapping into various energy sources to meet the body’s demands. Skeletal muscles rely on multiple metabolic pathways to produce ATP (adenosine triphosphate, the cell’s energy currency). The amount of ATP needed mostly depends on the intensity and duration of the exercise. Additional factors such as recent diet, training status, age, sex, body mass, and environmental conditions also play a role.

During any exercise, ATP is essential for activating and contracting skeletal muscles. Muscle cells only have a small reserve of ATP, meaning they cannot sustain contractions long without generating new ATP. For example, during an all-out 10-second sprint with a power output of around 1000 Watts, stored ATP would be depleted in about 2 seconds if it were the only energy source. Fortunately, skeletal muscles have well-developed metabolic pathways that can generate ATP rapidly for short periods of high-intensity exercise, while other, slower pathways support extended exercise sessions at lower intensities.

Fat and carbohydrates are the primary fuels for ATP production in skeletal muscles. The relative contribution of these fuels can vary significantly depending mainly on the exercise intensity [12, 13]. At rest, people without diabetes have low energy consumption almost exclusively yielded by fat combustion, depending on diet and prior exercise [13]. However, during exercise, there’s a significant shift in fuel use (Figure 1), mainly determined by the intensity and duration of the activity [13]. When exercising at intensities greater than ~60-70% of VO2max, carbohydrates (derived from muscle glycogen and plasma glucose) become the primary fuel source – a pattern that applies to people with T1D [14]. At an intensity of 100% VO2max, energy is almost exclusively produced from carbohydrates.

Several studies have investigated exercise-associated fuel metabolism in people with T1D and the effects of differing plasma glucose and insulin concentrations [14-19]. Overall, these studies show that individuals with T1D have a similar pattern of fuel use to those without diabetes, provided that glucose is within the normal range. However, some nuances are influenced by insulin levels (hyperinsulinaemia) and glucose availability (hyperglycaemia), which will be discussed further in Chapter 8.