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Effects of Food Restriction and Exercise upon the Deposition and Mobilization of Energy Stores in the Rat¹

Surgical Medical Research Institute, Department of Physical Education, and Department of Surgery, The University of Alberta, Edmonton, Alberta, Canada

The effects of pair-weighing and exercise upon the deposition and mobilization of energy stores were studied in male Wistar rats. Twelve sedentary animals (group 1) were fed ad libitum. Twelve animals (group 2) were fed ad libitum and trained to run on a rodent treadmill. The exercise program consisted of 12 weeks of running at 26.8 m/minute for 1 hour per day, 5 days per week. Group 3 was pair-weighed animals which had their food intakes restricted so as to result in a rate of weight gain similar to that of the exercised animals. On the day of sacrifice, one-half of the exercised animals were run to exhaustion. All other animals were sacrificed at rest. Resting blood glucose and lactate, plasma and adipose tissue free fatty acids, and skeletal muscle lactate values were similar for all groups. Liver and skeletal muscle glycogen values were similar for ad libitum and food-restricted sedentary rats. However, liver and skeletal muscle glycogen stores were significantly increased in all trained animals. Glycogen stores were nearly depleted and free fatty acids were significantly mobilized in the animals exercised to exhaustion. The results of this study indicate 1) that food restriction does not inhibit the deposition of glycogen in the liver or skeletal muscle of rats, 2) that regular enforced endurance exercise increases the deposition of hepatic and skeletal muscle glycogen, and 3) that long-lasting exhaustive exercise results in rapid mobilization of the energy substrates glycogen and free fatty acids.

KEY WORDS: • exercise • glycogen • glucose • lactate • free fatty acids • food restriction

¹ Supported in part by Grant no. 5505021 from the Department of National Health and Welfare, Ottawa.

² A. W. Taylor is the recipient of a Research Associateship from the Department of National Health and Welfare. Ottawa.

Manuscript received 15 June 1973.