Abstract
Different season trainings may influence autonomic and non-autonomic cardiac control of heart rate and provokes specific adaptations on heart’s structure in athletes. We investigated the influence of transition training (TT) and competitive training (CT) on resting heart rate, its mechanisms of control, spontaneous baroreflex sensitivity (BRS) and relationships between heart rate mechanisms and cardiac structure in professional cyclists (N = 10). Heart rate (ECG) and arterial blood pressure (Pulse Tonometry) were recorded continuously. Autonomic blockade was performed (atropine—0.04 mg.kg-1; esmolol—500 μg.kg-1 = 0.5 mg). Vagal effect, intrinsic heart rate, parasympathetic (n) and sympathetic (m) modulations, autonomic influence, autonomic balance and BRS were calculated. Plasma norepinephrine (high-pressure liquid chromatography) and cardiac structure (echocardiography) were evaluated. Resting heart rate was similar in TT and CT. However, vagal effect, intrinsic heart rate, autonomic influence and parasympathetic modulation (higher n value) decreased in CT (P≤0.05). Sympathetic modulation was similar in both trainings. The autonomic balance increased in CT but still showed parasympathetic predominance. Cardiac diameter, septum and posterior wall thickness and left ventricular mass also increased in CT (P<0.05) as well as diastolic function. We observed an inverse correlation between left ventricular diastolic diameter, septum and posterior wall thickness and left ventricular mass with intrinsic heart rate. Blood pressure and BRS were similar in both trainings. Intrinsic heart rate mechanism is predominant over vagal effect during CT, despite similar resting heart rate. Preserved blood pressure levels and BRS during CT are probably due to similar sympathetic modulation in both trainings.
Highlights
There are some evidences to suggest that training intensification might substantially influence autonomic control of heart rate (HR) [1,2,3], arterial blood pressure variability and baroreflex sensitivity (BRS) [1] in highly trained athletes, but the findings are controversial
Serum cortisol and hemoglobin levels were similar in transition training (TT) and competitive training (CT) respectively and hematocrit levels were higher in CT (45.6 ± 0.6 vs. 48.6 ± 1.1%, P = 0.01)
The present study provides evidence that season trainings influence the mechanisms of resting bradycardia in professional cyclists
Summary
There are some evidences to suggest that training intensification might substantially influence autonomic control of heart rate (HR) [1,2,3], arterial blood pressure variability and baroreflex sensitivity (BRS) [1] in highly trained athletes, but the findings are controversial. We had recently observed that professional cyclists compared to professional runners show higher participation of intrinsic over autonomic mechanism to explain their bradycardia [12] and an association between structural cardiac characteristic and intrinsic alterations, as suggested before [8, 12]. In view of these results, we could suppose that different trainings applied throughout training periodization would influence the intrinsic mechanism of resting HR. We expect an association between echocardiographic parameters and IHR
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