Effects of Exercise on Swimming Endurance and Organ Weight in Mature Rats

In an effort to study the effects of exercise on swimming endurance and organ weight, mature rats were divided into two groups. One group continued to be inactive while the other was allowed to exercise at will in individual cages. After three months the animals were forced to swim as long as they were able with 6 percent of the body weight attached. They were then sacrificed, and the organs were weighed. There was no evidence that spontaneous activity influenced organ weight or swimming endurance. It is suggested that the lack of effect may be due to the fact that (1) the animals were mature at the start of the experiment and (2) the amount of exercise taken voluntarily at the termination of the experiment was much less than had been the case when the animals were younger.