Training-related Changes In Cardiac Autonomic Function Assessed Before And After Graded Exercise Testing

Abstract

Aerobic training improves cardiac autonomic function, leading to increased heart rate variability (HRV) and decreased heart rate (HR) at rest. Intense exercise such as graded exercise testing (GXT) acutely increases HR and decreases HRV, which eventually return to resting levels post-exercise. Autonomic recovery after exercise may improve with training. PURPOSE: To examine the relationship between HRV and HR before and after GXT, and to assess changes resulting from 18 weeks of aerobic training. METHODS: Healthy young adults (n = 12, 7f; age 20.9 ± 0.6) completed physiological testing prior to enrollment in a marathon training course, and again after training. Testing included a 10-minute seated monitoring of HR/HRV (REST) with a Polar RS800cx watch and chest-strap, followed by GXT, and a 20-minute seated recovery period with HR/HRV monitoring. Recovery data were divided into two 10-minute segments (REC1 and REC2) for analysis. Mean HR and the following HRV measures were assessed using Kubios HRV Version 3.3: Standard deviation (SDNN), root mean square of the successive differences (RMSSD), high frequency power (HF), low frequency power (LF), low frequency to high frequency ratio (LF/HF), sample entropy (SE), and detrended fluctuation analysis α1 (DFAα1) and α2 (DFAα2). Repeated measures ANOVA was used to compare 10-minute segments (REST, REC1, and REC2) and to assess changes with training. RESULTS: All HRV measures and HR were different between segments (p ≤ 0.05), with HR lowest during REST and highest during REC1. Similarly, HRV measures reflected greatest variability during REST and lowest during REC1. Several measures of HRV, as well as HR changed with training. Heart rate decreased (p = 0.023) at REST (75.0 ± 17.3, 70.1 ± 14.2 bpm), during REC1 (106.3 ± 13.7, 100.1 ± 10.7) and REC2 (102.8 ± 11.9, 95.6 ± 10.3). With training, RMSSD increased (REST: 56.5 ± 29.3, 64.7 ± 32.4 ms; REC1: 6.8 ± 3.4, 8.5 ± 4.5; REC2: 9.4 ± 4.5, 11.1 ± 4.1; p = 0.048). Similarly, HF (p = 0.031) and DFAα1 (p = 0.017) exhibited greater variability across the three segments after training. CONCLUSIONS: Differences in cardiac autonomic function between timepoints before and after GXT were observed. Aerobic training reduced HR and increased selected HRV variables.