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

Abstract

We investigated the effects of aerobic training on the efferent autonomic control of heart rate (HR) during dynamic exercise in middleaged 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, V . O 2 AT; peak O 2 uptake, V . O 2 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 (∆0-10 s) related to vagal withdrawal (P<0.05, only at 25 watts) was observed in T at all powers; at middle and higher powers a significant decrease (P<0.05 at 50, 100 and 125 watts) in the slow tachycardia (∆1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) the V. O 2 AT (S = 1.06 and T = 1.33 l/min) and V . O 2 peak (S = 1.97 and T = 2.47 l/min) were higher in T (P<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.

Effects of aerobic exercise training on heart rate variability during wakefulness and sleep and cardiorespiratory responses of young and middle-aged healthy men

“…O 2 for the young group only, as well as an increase in power peak for both groups. This increase in aerobic capacity has been documented in other studies (10,15,16,21,22) for both anaerobic threshold and peak V . O 2 .…”

“…Concerning V . O 2 at the anaerobic threshold, the literature has also shown a decline of this parameter with advancing age (13) and there are studies indicating the occurrence of significant changes in aerobic capacity and autonomic changes in HR after aerobic training in middle-aged subjects (15,16).…”

Identification of anaerobic threshold using heart rate response during dynamic exercise

“…It corresponds to a point above a determined power value when the production of lactic acid is greater than the capacity of its utilization by body tissues (1,14). AT shows a good correlation with V .…”

“…In a study on post-menopausal women using DDET, Ribeiro et al (19) observed a loss of HR stability and a decrease in HR variability due to the prevalence of sympathetic activity on the sinus node. The inter-group differences in AT level are due to aging that markedly influences the cardiovascular system, promoting structural and functional changes (14). Takahashi et al (20), studying cardiac patients without the use of betablockers during physical exercise and with a discontinuous protocol, verified that by the adjustment of the semiparametric mathematical model to the HR data, the AT was identified at the power of 37.5 W and at HR of 100 bpm.…”

“…AT shows a good correlation with V . O 2max and has been proven to be very useful in quantifying oxygen transport and its modifications following physiological and pathological conditions (1,14). Several methods can be used to detect AT, including blood lactic acid sampling (invasive) (15) and changes in the response pattern of the ventilatory curves during continuous and incremental (non-invasive) dynamic physical exercise (1).…”