Further experimental results concerning the relationship of muscular exercise and adrenal function.

The relationship between muscular work and adrenal function was investigated by using daily swimming exercise in the rat. 1. Adrenal in vitro sensitivity to ACTH was found to have increased after six weeks of swimming training 2. In the development of adaptation the main part was played by muscular exercise itself, since a conditioning of the animals merely to the circumstances of swimming failed to stimulate such adaptive changes as seen in the course of regular physical training. 3. Plasma steroid response to certain stressor agents, such as histamine or acute exhaustion (decrease), respectively to ACTH administration (increase) was similar in ACTH-pretreated and regularly exercised animals. 4. In the 6th to 12th weeks of exercise the trained animals developed a lower plasma steroid content at rest than the controls. This feature was retained even four weeks after the cessation of training sessions. Experimental physical training reduced post-exercise steroidemia in the period of adaptation, that is, after the 6th week. After a pause of 4 weeks, however, the post-exercise steroidemia approached again the control values.