During a twelve week period the effects of a controlled program of progressive endurance training on 30 healthy young conscripts were studied during five different psychophysical loading situations. The control group (10 Ss) were trained by a supposed mock load and therefore had a steady state heart rate of about 90 per minute during training on a bicycle ergometer. The other two groups (10 + 10 Ss) pedalled four days a week, thirty minutes at a time and had a heart rat; of about 140 and 160 per minute, respectively. With some loss of samples the urinary excretion of noradrenaline, adrenaline and 17-hydroxycorticosteroids, the concentration of plasma lactic acid, potassium sodium and the blood glucose were determined (1) during relative rest situations, (2) after submaximal six-minute and (3) thirty-minute muscular work on a bicycle ergometer, (4) during a four-hour military march after the Ss had stayed awake the preceding night and (5) after a highly motivated competition in a choic
e reaction test lasting about an hour, Both the steady heart rate during standardized ergometric work and the performance during the choice reaction test competition were also determined. In comparison with the relative rest situation, a significant increase was found in the urinary excretion of noradrenaline and in the ratio of noradrenaline to adrenaline but not in the adrenaline or 17-bydroxycorticosteroids excretion after the loading situations. The lactic acid concentration in the plasma was significantly higher after both ergometric tasks as compared to the relative rest situation. The significant changes in blood glucose concentration were obviously more due to the dietary system. No consistant significant effect on ionic concentrations was found in this study. After the training a significantly lower heart rate during ergometric work was found in the trained group. However, such a significant difference was not found in the lactic acid concentration during the submaximal anaerobic work on a bicycle ergometer. During the four-hour march after the training the concentration of blood glucose in the trained group was significantly higher, the urinary excretion of noradrenaline in the forenoon of a control day significantly higher, and the adrenaline excretion in the afternoon of a control day significantly lower than in the control group. After a short anaerobic loading the concentration of the plasma K⁺ significantly higher, and the ratio of Na⁺ to K⁺ significantly lower in the trained group. This ratio was lower in the trained subjects even after the more aerobic work on a bicycle, No consistency in the significant Na⁺ differences was found.
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