Relationship between sympathetic and adrenomedullary activities during exercise. With reference to duration of exercise / 体力科学

This study was designed to evaluate the effect of exercise duration on the relation between sympathetic and adrenomedullary activities. Six trained subjects completed the following two exercise protocols ; six 2-min exercise sessions at 100% maximal O<SUB>2</SUB>uptake (VO<SUB>2</SUB>max) interspersed with 10-min recovery periods, and three 10-min exercise sessions at 80%VO<SUB>2</SUB>max interspersed with 10-min recovery periods. Plasma noradrenaline (NA), plasma adrenaline (A), NA/A ratio (NA/A), heart rate (HR), coefficient of variation of R-R intervals (CVRR) and blood lactate (La) were measured. With repetition of exercise sessions in both protocols, HR, NA and A gradually increased. CVRR rapidly decreased at the first exercise session and remained unchanged thereafter. NA/A increased by the first exercise session, but decreased by the following exercise sessions. NA in the second exercise session at 100%VO<SUB>2</SUB>max was significantly lower than that in the first. We conclude that, at the beginning of exercise, the increase of sympathetic activity is more dominant than that of adrenomedullary activity, whereas, with prolongation of exercise duration, the increase of adrenomedullary activity becomes more dominant than that of sympathetic activity,

Heart rate and plasma catecholamines responses to exercise at various intensities / 体力科学

To investigate the responses of heart rate and plasma catecholamines to exercise at various intensities, seven healthy adult males performed 6-min bouts of cycling exercise at 30, 50, 70 and 90% of maximal oxygen consumption (VO<SUB>2</SUB>max) . Heart rate (HR), plasma noradrenaline (NA), plasma adrenaline (A), blood lactate (La) and coefficient of variation of R-R intervals (CVRR) were determined i n each case.<BR>The following results were obtained:<BR>1) CVRR showed a sharp decline to the extent of 50%VO<SUB>2</SUB>max, then fell more slightly for heavier exercise.<BR>2) NA and A significantly increased from resting value at 50%VO<SUB>2</SUB>max, and followed by further increase with exercise intensity. NA/A increasd in proportion to exercise intensity.<BR>3) The results of multiple regression analysis of HR (dependent variable) and NA, A and CVRR (independent variables) indicated the greatest standardized partial regression coefficient for CVRR in the case of low intensity exercise, and for NA with high intensity exercise.<BR>4) La increased abruptly at 70%VO<SUB>2</SUB>max, whereas NA and A rose drastically at 90%VO<SUB>2</SUB>max.<BR>The conclusion based on these results is as follows: HR is mainly influenced by change in parasympathetic tone to the extent of 50%VO<SUB>2</SUB>max, whereas sympathetic and adrenomedullary activity are the main factors controlling HR in heavier exercise. Within the submaximal level of exercise, sympathetic activity increases more markedly than that of adrenomedullary activity. Abrupt increase in La may be independent of catecholamines.