Thirteen female swimmers (ranging in age from 15 to 18 years) were selected as subjects and divided into two groups; group A (subjects of experiment) consisted of six subjects in whom low pressure was loaded and group B (subjects of control) consisted of seven in whom low pressure was not given.
During training, circuit weight training was performed in a low pressure environment and it was combined with conventional swimming training. We studied the effect of these types of training on their red-cell 2, 3-diphosphoglycerate, salivary cortisol, and plasma testosterone.
(1) The 2, 3-DPG level showed a greater increase after loading exercise than at the time of resting in both groups A and B. The increase was highly significant in group A. Additionally, 10 days after the removal of the loading, hemoglobin and hematocrit levels were significantly decreased in groups A and B, and a significant increase in 2, 3-DPG was observed in group A.
(2) Only after loading low pressure was the cortisol level higher in group A than in group B. However, there was no significant difference between the two groups in the amount of exercise loading when heart rate was used as the index.
(3) Testosterone tended to show a greater increase after exercise loading than on the first day of the experiment. However, neither an effect of exposure to low pressure on testosterone nor a significant difference between the two groups was observed.
According to the results, in swimming, an endurance contest, physical changes during training are almost the same in group A and B, but it is considered that a concurrent severe hypoxic condition as a result of low pressure loading brings about homeostasis in the living body and the homeostasis leads to an attempt to increase oxygen uptake by the tissues, yeilding increased staying power.

We determined the release of β-endorphin and prolactin into the blood, before and after 60-minute exercise of acute cycle ergometer in five healthy students and three athletes. This exercise induced an increase in circulating mean β-endorphin level [basal to after exercise level, 14.9±0.7 (mean±SE) pg/ml→57.1±17.0 pg/ml : p<0.05] and mean prolactin level [9.4±0.7 ng/ml→9.1±3.1 ng/ml : p<0.01] . There was a significant correlation between β-endorphin and prolactin values in all samples (r=0.892: p<0.01 : n=32) . Athletes tended to release greater amounts of β-endorphin and prolactin into the blood than students after acute exercise.
We find that acute exercise stimulates release of β-endorphin and prolactin in parallel and athletes have increased plasma β-endorphin and prolactin after acute exercise.

We determined the release of β-endorphin and prolactin into the blood, before and after 60-minute exercise of acute cycle ergometer in five healthy students and three athletes. This exercise induced an increase in circulating mean β-endorphin level [basal to after exercise level, 14.9±0.7 (mean±SE) pg/ml→57.1±17.0 pg/ml : p<0.05] and mean prolactin level [9.4±0.7 ng/ml→9.1±3.1 ng/ml : p<0.01] . There was a significant correlation between β-endorphin and prolactin values in all samples (r=0.892: p<0.01 : n=32) . Athletes tended to release greater amounts of β-endorphin and prolactin into the blood than students after acute exercise.
We find that acute exercise stimulates release of β-endorphin and prolactin in parallel and athletes have increased plasma β-endorphin and prolactin after acute exercise.