Pyramid Science

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Thursday, December 25, 2008


In mammals the blood is the transport mechanism of the human body and supplies nutrients to every cell. Poor circulation will cause some muscles to tire easily or at least not receive these nutrients. The main sources of energy in food are from protein, carbohydrate and fat. Calories are not eaten, but these food sources do provide energy. It is the energy potentially available if the food is burnt by the body as a fuel. If it is not needed then this potential fuel source is stored. Carbohydrate is converted into fat and stored by the body.

Consequently, the depot fat (stored by the body for later use) will increase if such foods are eaten and the energy requirement is not reached to consume this amount. The body is particularly efficient at doing this. Starvation diets do not work, and are dangerous for many reasons, because the body will go into starvation mode when it realises it is losing body material too fast. The metabolism slows to minimise this loss and the body fat is retained to some extent. So, when short term dieting is over, the old eating habits return, but with a slowed metabolism. What happens? You get fatter than you were! The availability of the potential for energy from these food sources is different. About 4kcal/g each from carbohydrate and protein but 9kcal/g from fat.

The fat content of food is a more compact form of energy. What this means is that for every 1g fat consumed, there is 9/4 = 2.25 times the energy available compared to 1g of each of the other two. Put another way, given a particular energy requirement needed for an activity, less than half the amount of fat would be burnt as fuel as would carbohydrate (the main muscle fuel) or protein. Indeed, to satisfy a balance of energy from food in work expended then less than half the weight of fat can be consumed as carbohydrate or again, put another way, over twice the carbohydrate g/g can be eaten. Consider the nutritional values of a typical chocolate cake.

Energy per 100g:
  • Protein 6.0g
  • Fat 16.0g
  • Carbohydrate 56.0g
The total weight is 78g (the 22g deficit is made up of water and other trace constituents). The fat content may only appear to be

16/78 = 20%

by weight. However, energy wise the picture is quite different.

  • Protein: 6 x 4 = 24kcal
  • Fat: 16 x 9 = 144kcal
  • Carbohydrate: 56 x 4 = 224kcal
  • Total = 392kcal
The fat content in energy terms is actually

144/392 =37%

nearly double. You must be very careful about how nutritional values are interpreted.

Intensity of Work

The intensity of muscle work can be estimated by using the modified Karvonen Equation to calculate your target heart rate (THR). Aerobic work is achieved in a muscle working at about 60-85% capacity. Such a muscle is able to completely burn the fat/carbohydrate fuel with the oxygen inhaled producing carbon dioxide and water as the only biproducts. The exhalation cycle in respiration removes the gaseous carbon dioxide and water as vapour.

Energy Pathways for Exercise

Anaerobic work at a higher intensity is when the need for energy cannot be supplied fast enough by the same mechanism and an alternative pathway is necessary. No oxygen is needed for this but the biproducts are different. Lactic acid is formed which causes the stiffness and soreness in muscle if it is allowed to build up in the anaerobic process. Lactic acid is completely removed but only much later after the muscle work is over.

Continued faster respiration, puffing or blowing depending on the actual intensity level, for an extended period after exercising ensures that sufficient oxygen is eventually supplied by the blood to do this. This is the oxygen debt - the deficiency of oxygen must be paid back. In some muscles the blood flow is not sufficient to supply enough oxygen for the aerobic mechanism to work in untrained muscles and lactic acid builds up as a result of anaerobic oxidation. This insufficiency also ensures that these biproducts are not removed completely and soreness and stiffness occurs. As the muscle is worked (trained) the blood supply improves so enough oxygen will be supplied to ensure aerobic oxidation so that stiffness does not occur. The training effect.


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