Metabolic stress of endurance swimming in the laboratory rat.

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Abstract
By means of closed-circuit spirometry the oxygen consumption of 17 trained, male albino rats was determined under conditions of rest and swimming with no weight and with loads equivalent to 0.5, 1.0, 1.5, and 2.0% of the body weight attached to the tail. Upon completion of the exercise, recovery metabolism was recorded for 25 min. It was concluded: 1) The exercise oxygen consumption of nonweighted animals averaged 2.7 times the resting level. In animals able to swim without apparent difficulty, this increased with the addition of weight to 3.5-fold at a load equivalent to 2.0% body weight. 2) With the addition of weight many animals had difficulty swimming at the surface of the water. This difficulty was reflected in a decreased aerobic metabolism which actually was less than the average of the nonweighted trials. 3) The oxygen consumption in milliliters per kilogram per minute at rest and at all levels of exercise was negatively correlated with body weight. 4) The rate of recovery was dependent upon the preceding exercise stress; i. e., the heavier the weight attached during swimming, the slower the recovery.