Body Fat, Fatty Acids - Prolonged Low Intensity Physical Exercise Fuel

Most of the stored energy in our bodies is found in the fatty acids of triglycerides. Most of it exists in adipose tissue (body fat deposits). When those deposits of fat stores are broken down for the production of energy, triglyceride molecules yield fatty acids that through the blood stream travel to the muscles.

Fatty acids from here move to mitochondria (energy factories) where they are broken down into carbon dioxide and water using the electron transport-chain, oxygen requiring electron carriers), for the production of energy, adenosine triphosphate (ATP). The rate at which muscles use fatty acids depends on several factors.

The Use of Fatty Acids

• The more fatty acids released from adipose tissue in the blood stream the more fat will be used by the muscles as energy. A practice that can increase the release of fatty acids in the blood stream from body fat tissue, employed by many athletes, is the consumption of caffeine containing beverages.

• The more conditioned a muscle is, regular exercise and/or physical activity, the greater its ability to utilize fat as a fuel for energy. Aerobic exercise and training after some period of time enables muscle cells to produce more ATP, from oxygen requiring pathways including the pathway used to burn fat for fuel. This becomes possible because muscle cells will develop more and larger mitochondria.

• When exercise increasingly becomes longer but remains at low to moderate aerobic rate the use of fat as a source of energy predominates. When there is demand for energy, for long duration physical activity or exercise, while stores of carbohydrates are always limited there is almost always plenty of fat supply to provide it. Fat actually supplies more than twice as much energy as carbohydrate does for a given weight of fuel.

The aerobically utilization of one glucosemolecule (6-carbon) produces 30 to 32 ATP while a fatty acid molecule (16-carbon) produces 108 ATP. However, carbohydrate is more efficient in one special way. It takes 23 O2 molecules to produce 108 ATP but it takes only 6 O2 molecules to produce 30 to 32 ATP. This means athletes involved in competitive endurance exercise need that muscles cells also use carbohydrate as long as the supply lasts.

When engaging in lengthy physical activities or exercise such as ultra marathon, manual labor and even a desk job for 8 hours a day adipose stores (fat) provide the energy requirements for prolonged low intensity exercise ( 70% to 90%). It is only carbohydrate however that can support intense aerobic activity or exercise. Prolonged low intensity steady exercise or activity uses all available energy, fat and carbohydrates.

fatty acids, body fat, low intensity exercise

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