PLASMA-CATECHOLAMINES DURING ENDURANCE EXERCISE OF DIFFERENT INTENSITIES AS RELATED TO THE INDIVIDUAL ANAEROBIC THRESHOLD

The study investigated the concentrations of free plasma catecholamine s (CAT), adrenaline and noradrenaline, in comparison to heart rate and lactic acid concentrations during endurance exercises (EE) of differe nt intensities related to the individual anaerobic threshold (IAT). A group of 14 endurance trained male athletes took part in the tests on a treadmill. After an exhausting incremental graded test (increasing 0 .5 m.s(-1) every 3 min) to determine the IAT, the subjects performed E E of 45 min in randomized order with intensities of 85%, 95%, 100% and 105% (E85-E105) of the IAT. The heart rate and CAT increased continuo usly during all EE. The CAT reacted sensitively to EE above IAT (E105) and showed an overproportional increase in comparison to EE performed with an intensity at or below IAT. At the same time, at exercise inte nsities up to IAT (E85-E100) a lactate steady state was observed where as mean lactate concentrations increased during E105. The changes of l actate concentration allowed a better differentiation between E85-E100 as CAT measurements. In E95, E100 and E105 there was a partial overla p of heart rate, which in contrast to lactate concentration only diffe red by about 5%, so that small variations in heart rate could have coi ncided with considerable differences of exercise intensity when workin g at intensities near or above IAT. It was concluded that the range of IAT seemed to represent a real physiological breakpoint which corresp onded to the aerobic-anaerobic transition.