Endurance
The body's ability to sustain prolonged effort, relying on the efficiency of the cardiovascular system, the mitochondria and the management of energy reserves.
Endurance is the ability to keep up an effort over time. It depends on VO2 max, lactate threshold, energy efficiency and the ability to use fat as fuel.
The original angle (metabolic flexibility): a high-performing endurance athlete has a well-developed metabolic flexibility: the ability to switch easily from carbohydrate fuel to fat fuel depending on intensity.
At low and medium intensity, the body favours fat (almost unlimited reserves). At high intensity, it switches to glycogen (limited reserves, ~90 min). A trained athlete “spares” glycogen by burning more fat at moderate intensity, hence better endurance.
Nutrition strategies:
- Efforts < 60-90 min: no need to refuel, reserves are enough
- Efforts > 90 min: take in carbohydrate during the effort (30-60 g/h) to spare glycogen and delay “the wall”
- “Train low, compete high”: some athletes sometimes train with low glycogen stores to stimulate adaptations (more mitochondria, better use of fat), then reload for competition
The marathon runner’s wall: at around 30-35 km, glycogen runs out. Without refuelling, performance collapses abruptly (“hitting the wall”). A good carbohydrate strategy and training in fat oxidation prevent this.
Endurance is also built through mitochondrial biogenesis: training creates more mitochondria, increasing the capacity to produce energy aerobically.