Background
Increased endurance exercise may cause an acute reduction in cardiac function, causing a physiological cascade. Heart rate variability (HRV) is a physiological measurement used to evaluate the autonomic nervous system (ANS) state. This study set out to determine the changes in the ANS by participating in a three-day mountain bike cycling event using HRV as an outcome measure.
Methods
Sixteen healthy participants (male and female) participating in a three-day mountain bike cycling event underwent five-minute resting electrocardiography (ECG) recordings in a supine position. In addition, heart rate variability measurements were recorded two days before the race (baseline testing), after each race day, and 24-hours post-event (recovery).
Results
Time-domain and frequency domain measures showed significant changes from baseline HRV parameters after each race day (p ≤ 0.05). In addition, our data revealed that the mean heart rate (HR) and R-R variability intervals did not return to baseline values after 24-hours of recovery. Thus, reflecting autonomic nervous system (ANS) dysfunction due to increased sympathetic activity and parasympathetic withdrawal.
Conclusions
The main strength of this study is using HRV as a measuring and screening tool to assess cardiac autonomic activity, whereby the state of the ANS before and after endurance events can be measured. Thus, physicians, athletes, and coaches can assess the stress of endurance events on the ANS and plan for correct recovery strategies. The reasoning is that if the ANS is in a state of dysfunction, susceptible amateur athletes might be at risk for a cardiovascular event.