Influence of Diet on Muscular Efficiency

Many attempts have been made to demonstrate a greater mechanical efficiency of the body (less energy expenditure in the performance of a given amount of work) on a diet in which one or another of the major foodstuffs predominates. The modern opinion, is that the efficiency is practically the same on all diets. There is a slight increase in efficiency following a high carbohydrate diet, but probably not more than 5 per cent.

The influence of diet is more clear-cut on another aspect of muscular activity, the working capacity or ability to perform work without early onset of fatigue. Experiments indicated that a high fat diet resulted in greater distress and an earlier onset of fatigue titan did an average mixed diet. Working at an intensity of 7,800 foot-pounds per minute, was aide to continue three times as long on a carbohydrate diet as on a fat diet. This may be associated with the fact that fat metabolism is more prone to result in the production of acid metabolites than is the metabolism of carbohydrate, and a rise in tissue acidity is generally regarded as favoring the onset of fatigue.

Carbohydrate is of primary importance as a fuel for muscular exercise in man. During prolonged work, eventual depletion of the carbohydrate stores (principally liver and muscle glycogen) may force the muscles to obtain a significant proportion of their energy from fat and protein. This is probably an indirect process, involving a preliminary conversion to carbohydrate before oxidation. Muscular efficiency is slightly greater, and the onset of fatigue is postponed, on a high carbohydrate diet. The blood sugar is normal or elevated in light and moderate work and in strenuous work of short duration, so that "priming" with sugar is of no particular advantage. In prolonged strenuous exertion, exhaustion may result from lowering of the blood sugar brought on by depletion of liver glycogen; the administration of sugar is often very definitely beneficial.There is no evidence that hard physical work necessitates an increased intake of protein.