Abstract
To assess changes of β-endorphin during intense endurance exercise, ten nonspecifically
trained volunteers (aged 25.7±2.9 years) were subjected to an exhaustive endurance
test on a cycle ergometer at the work load of the individual anaerobic threshold (IAT)
determined in a preparatory graded exercise test. Prior to, in 25-min intervals during,
and repeatedly subsequent to exercise venous blood samples were drawn to measure the
levels of β-endorphin (β-E), cortisol (C), adrenaline (A), and noradrenaline (NA).
In addition, lactate, heart rate, and rate of perceived exertion were determined.
The levels of β-E remained unchanged during the first 50 min; between the 50th and
75th min β-E increased by 82% (p<0.01). At the end of the exercise (mean exercise
time: 89 min), a β-E level three times the resting level was measured. The maximum
exercise-induced increase of β-E showed a positive correlation to endurance capacity
(W·kg-1 of IAT): r=0.74; p<0.05. C exhibited similar changes to β-E, but the onset of increase
was delayed if compared with β-E; there was a close correlation between these two
stress hormones (75th min of exercise: r=0.91; p<0.001). The catecholamines A and
NA increased linearly during exercise, without a correlation with the behavior of
β-E being established.
It can be concluded that intense endurance training leads to an increase in β-E only
beyond an exercise duration of approximately 1 h.
Key words
β-endorphin - stress hormones - anaerobic threshold - prolonged exercise
