How does the depletion of fuel sources in the aerobic energy system contribute to an athlete "hitting the wall" during a marathon at around the 32-kilometre mark? (5 marks)
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- Marathon runners begin by using both carbohydrate and fat for fuel, with glycogen providing easy energy at steady pace.
- After about 2 hours, muscle glycogen stores run very low, which forces the body to use mainly fat for energy.
- Fat needs more oxygen to make ATP than carbohydrate does, resulting in higher oxygen demands that the body cannot meet at the same running speed.
- This change causes runners to slow down immediately as their bodies cannot get enough oxygen for the pace.
- Body temperature goes up because fat burning is less efficient, creating extra heat that makes runners feel hotter.
- Breathing rate increases to get more oxygen for fat burning, which makes runners feel breathless even though they’ve slowed down.
- The brain also lacks glucose, causing poor concentration and less motivation to continue.
- These problems together create the sudden tiredness known as “hitting the wall”.
- Therefore, glycogen depletion forces the body to use harder-to-burn fat for fuel.
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Sample Answer
- Marathon runners begin by using both carbohydrate and fat for fuel, with glycogen providing easy energy at steady pace.
- After about 2 hours, muscle glycogen stores run very low, which forces the body to use mainly fat for energy.
- Fat needs more oxygen to make ATP than carbohydrate does, resulting in higher oxygen demands that the body cannot meet at the same running speed.
- This change causes runners to slow down immediately as their bodies cannot get enough oxygen for the pace.
- Body temperature goes up because fat burning is less efficient, creating extra heat that makes runners feel hotter.
- Breathing rate increases to get more oxygen for fat burning, which makes runners feel breathless even though they’ve slowed down.
- The brain also lacks glucose, causing poor concentration and less motivation to continue.
- These problems together create the sudden tiredness known as “hitting the wall”.
- Therefore, glycogen depletion forces the body to use harder-to-burn fat for fuel.