Depletion of Tissue Glycogen During Fasting and Fatigue and Partial Recovery Without Food

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Abstract
The glycogen content of paired muscles removed from rats killed by a blow on the head was compared with that of animals anaesthetized with amytal. Much more closely agreeing results were obtained from the live anaesthetized animals. The effect of fasting, of exposure to cold, and of various kinds and amounts of exercise (running ad libitum in revolving cages, forced running on a treadmill, and swimming in water at different temperatures) was investigated. A 24-hour fasting period reduced the liver glycogen to a very low level, which was depressed only slightly more by the fatiguing exercise. It reduced the muscle glycogen by one-third; after 24 hours the rate of fall was much slower. Fatiguing exercise while fasting decreased the muscle glycogen content to a much lower level. During the recovery period after fatigue by swimming 8 hours, a small amount of glycogenesis occurred, notwithstanding the fasting state. The liver glycogen was not much affected until the third hour, when it reached a level twice as high as that observed after fasting only. The muscle glycogen rose notably during the first 2 hours, but only slightly in the third hour.