Cardiorespiratory adaptations induced by aerobic training in middle-aged men: the importance of a decrease in sympathetic stimulation for the contribution of dynamic exercise tachycardia

• Main Author: Chacon-Mikahil,M.P.T.
• Publication Date: 1998
• Other Authors: Forti,V.A.M., Catai,A.M., Szrajer,J.S., Golfetti,R., Martins,L.E.B., Lima-Filho,E.C., Wanderley,J.S., Marin-Neto,J.A., Maciel,B.C., Gallo-Jr.,L.
• Format: Article
• Language: eng
• Source: Brazilian Journal of Medical and Biological Research
• Download full: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X1998000500016
• topic: sympathetic modulation of heart rate; dynamic exercise; aerobic training; autonomic nervous system; anaerobic threshold; middle-aged men

We investigated the effects of aerobic training on the efferent autonomic control of heart rate (HR) during dynamic exercise in middle-aged men, eight of whom underwent exercise training (T) while the other seven continued their sedentary (S) life style. The training was conducted over 10 months (three 1-h sessions/week on a field track at 70-85% of the peak HR). The contribution of sympathetic and parasympathetic exercise tachycardia was determined in terms of differences in the time constant effects on the HR response obtained using a discontinuous protocol (4-min tests at 25, 50, 100 and 125 watts on a cycle ergometer), and a continuous protocol (25 watts/min until exhaustion) allowed the quantification of the parameters (anaerobic threshold, VO2 AT; peak O2 uptake, VO2 peak; power peak) that reflect oxygen transport. The results obtained for the S and the T groups were: 1) a smaller resting HR in T (66 beats/min) when compared to S (84 beats/min); 2) during exercise, a small increase in the fast tachycardia (<FONT FACE="Symbol">D</font>0-10 s) related to vagal withdrawal (P&lt;0.05, only at 25 watts) was observed in T at all powers; at middle and higher powers a significant decrease (P&lt;0.05 at 50, 100 and 125 watts) in the slow tachycardia (<FONT FACE="Symbol">D</font>1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) the VO2 AT (S = 1.06 and T = 1.33 l/min) and VO2 peak (S = 1.97 and T = 2.47 l/min) were higher in T (P&lt;0.05). These results demonstrate that aerobic training can induce significant physiological adaptations in middle-aged men, mainly expressed as a decrease in the sympathetic effects on heart rate associated with an increase in oxygen transport during dynamic exercise.