Chapter 3 Nutrition

Going the extra mile

Targeted supplementation

Maximising performance


We all need energy for exercise. Energy is the basic requirement for any form of activity.

It comes from the food we eat and fluids we drink but how much is enough? Too little and we run the risk of under-performing and getting fatigued, too much and we gain weight. What form of exercise we perform also plays a role. Whether we are involved in endurance or explosive activities or whether we are watching our weight, or male or female, we all need energy to exercise but the balance of that energy requirement varies from one to the other.

How quickly we need that energy is also a factor. If we need the energy over a 20 s sprint, then it has to be quickly and freely available as opposed to the slow drip feed supply of a marathon runner. Where that energy is stored and available is important and this reflects the form of energy we take in.

Energy production

The unit of energy is ATP (adenosine triphosphate) which when broken down releases energy. There are three systems of releasing energy from ATP which work together to provide the energy requirement depending on what exercise regime is being followed.1


2. Anaerobic energy

3. Aerobic energy

Some athletic events require purely one energy system to be utilised but most require a combination of all three (Fig. 3.4). Training fine tunes the efficiency of each system appropriate to the event which is being trained for.


The different types of energy sources and their sub-divisions can be confusing and distracting. The three sources of energy are as follows2:

1. Carbohydrates

2. Proteins

3. Fats


Glucose is stored in the form of glycogen in muscles and in the liver and is the preferred and most efficient source of energy. Glycogen stores are relatively small and run out after a few days of exercise if not replenished. The amount needed to be re-stocked depends on the exercise regime that is being followed.

The bulk of carbohydrate should come from cereals or starchy food sources such as:

The remainder is gained from sugar, fruits and juices.

You should tailor your intake to your energy expenditure, so if you have a high daily load of intensive exercise you should have an equally high carbohydrate intake, with regular snacks in-between feeds.

The speed with which the glucose is absorbed into the blood stream and hence its availability as a substrate for energy release is also a factor in your choice of carbohydrate foods. The glycaemic index (GI)3 is a measure of this. Highly absorbed carbohydrates have a high GI index and poorly absorbed ones have a low GI index. The high GI foods are useful to take as recovery after exercise when carbohydrate stores need to be re-stocked quickly, and low GI foods, which have higher fibre contents, release their energy sources more slowly. Examples of high and low GI foods are shown in Table 3.1.

Table 3.1 High and low GI foods

  High GI Low GI
Breads Bagel, wholemeal Granary, rye bread
Cereals Bran flakes, Weetabix Muesli, All-bran
Starches Baked/mashed potato Pasta, lentils
Fruit Watermelon Apple, peach, pear
Snacks Jelly beans, rice cakes Sultanas, Mars bar
Drinks Sports drinks (isotonic) Apple/Orange juice

Stay updated, free articles. Join our Telegram channel

Jul 18, 2016 | Posted by in SPORT MEDICINE | Comments Off on Nutrition

Full access? Get Clinical Tree

Get Clinical Tree app for offline access