Describe the metabolic response to exercise and the factors that influence the choice of fuel.

1. 1 · Open in two lines. Exercise raises energy demand many times over. The body responds with hormonal, metabolic and circulatory changes and picks its fuel by intensity and duration.
2. 2 · Draw the oxygen uptake curve. [Graph: oxygen uptake vs time: deficit at the start, steady state, EPOC after exercise]
3. 3 · Metabolic and hormonal response.
   • Adrenaline, glucagon, cortisol, GH up; insulin down.
   • Glycogenolysis, lipolysis, gluconeogenesis.
   • Lactate threshold.
4. 4 · Heart, lungs, blood flow and heat. Cardiac output and breathing rise; blood goes to muscle and skin; temperature rises and sweating starts.
5. 5 · Factors influencing fuel choice.
   • Intensity: the crossover concept.
   • Duration.
   • Training status.
   • Diet before and during exercise.
   • Sex, environment, fibre type.
6. 6 · RQ. Carbohydrate 1.0, fat 0.7, protein about 0.8; RER can exceed 1.0 in very hard work.
7. 7 · Nutrition link. High-intensity sports run on carbohydrate, so glycogen stores must be full before matches.
8. 8 · Close in one line. Intensity is the master switch: the harder the work, the more the body depends on carbohydrate.

Scoring tip: A labelled oxygen-uptake curve and the crossover line in one sentence give the answer its backbone.