Fuel depletion, dehydration and fatigue

Overview

Fatigue from phosphocreatine and glycogen depletion, hitting the wall and running on fat, sweating and the blood, temperature control, the fluid loss that impairs performance with a worked example, electrolytes, decision-making, and the triathlete.

What you need to know

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Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is fatigue in a sporting context?

   Model answer

   Fatigue is a decline in the ability to keep producing force or power. Performance falls as a result.

2. 2

   How does running out of phosphocreatine cause fatigue in a 100 m sprint?

   Model answer

   Phosphocreatine stores last only about 8 to 10 seconds of maximal effort. ATP then cannot be resynthesised fast enough, so the sprinter slows near the finish.

3. 3

   Why does glycogen depletion cause fatigue late in a marathon?

   Model answer

   Muscle and liver glycogen stores are limited and fall steadily during a long race. Fat becomes the main fuel, and fat cannot supply energy quickly enough to hold race pace.

4. 4

   What is meant by hitting the wall in endurance sport?

   Model answer

   The wall is the sudden, severe fatigue felt when muscle glycogen runs out. A marathon runner who hits it is forced to slow down sharply.

5. 5

   Why can a performer keep going after glycogen runs out, but only at a lower intensity?

   Model answer

   Fat can still be broken down aerobically once glycogen is gone. Fat needs more oxygen per unit of energy, so only a slower pace can be supplied.

6. 6

   How does heavy sweating affect the blood during exercise?

   Model answer

   Sweat loss reduces the volume of blood plasma. The blood becomes more viscous, so it flows less easily to the working muscles.

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