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Eating to win: activity, diet and weight control
Eating to win: activity, diet and weight control

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3 Fitness and fat metabolism

Fitness levels contribute to our energy expenditure and weight control. As fitness improves it is possible to do more work at the same heart rate and level of perceived exertion; you are able to burn more energy for the same perceived effort. The term metabolism means the breakdown of foods to release energy. You can metabolise fat, carbohydrate or protein to release energy.

In the following activity, you will learn about the link between fitness level and fat metabolism.

Activity 2 Fitness and fat

Timing: Allow about 30 minutes

Read from ‘Increased caloric expenditure’ up to, but not including, the subsection ‘Reduced blood lipids’ on pages 323–326 from Chapter 13 of the book Fitness and Health by Sharkey and Gaskill (2013) [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .

As you read, answer the following questions:

  1. What is the link between increased fitness and caloric expenditure?
  2. What is the relationship between lactic acid and the use of fatty acids as a source of energy?
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  1. As your fitness level improves your caloric expenditure increases. This is because you generally increase your frequency, duration and intensity of exercise.
  2. At high intensities of exercise, fat and carbohydrate cannot be broken down quickly enough to provide energy, so carbohydrates are metabolised to provide the energy needed quickly, resulting in increases of lactic acid. The presence of lactic acid also blocks the action of epinephrine (adrenalin), which is needed to allow the fatty acids to be used as energy. When your fitness improves, you are able to perform exercise at a higher intensity with less of an increase in lactic acid. This means that you are more able to utilise fat as an energy source.

Having explored how improved fitness can enable us to metabolise fat, you will now look at the effects of diet and exercise on fats in the blood.