Heart Rate Variability At Rest And During Steady State Exercise In Marathon Training Students

Abstract

Heart rate variability (HRV) and heart rate (HR) at rest are known measures of health and adaptability, with higher HRV and lower HR associated with greater parasympathetic tone. While HRV is dramatically reduced during exercise, some research indicates that a relationship between health and/or fitness and HRV can be seen during steady state exercise (SSX). PURPOSE: To examine the relationship between HRV at rest and during SSX, and to assess whether HR and HRV change in response to marathon training. METHODS: College students (n = 39; 25F age 21.0 ± 1.5) enrolled in a marathon training class ran a 2-mile time trial (2MI) followed by physiological testing 1-2 weeks later. Testing included hydrostatic weighing for body fat percentage (%BF), 10-min.[m1] monitoring of resting HR/HRV, SSX (a 6-min. run at 75% velocity of 2MI), and a graded exercise test for VO2max. A subset of 15 participants returned for post-testing after an 18-week training program. After assessment for artifact, SSX data was used for 33 (pre) and 10 (post) participants. Resting HR/HRV and the final 3 min. of SSX HR/HRV data were used to calculate HR and the following measures of HRV: standard deviation (SDNN), root mean square of the successive differences (RMSSD), high frequency power (HF), sample entropy, and detrended fluctuation analysis α1 (DFAα1) and α2 (DFAα2). Pearson’s correlations were used to assess relationships between variables, and paired samples t-tests were used to examine changes with training. RESULTS: Pre- and post-training measures of resting HRV were positively correlated with each other and negatively correlated with resting HR (p ≤ 0.01). Resting SDNN and RMSSD were also negatively correlated with %BF (p ≤ 0.05). Measures of HRV during SSX were correlated with each other but not with HRV at rest[m2]. Measures of HRV at rest but not during SSX changed with training. At rest, HR decreased (78 ± 18, 70.6 ± 13.2 [m3] bpm; p = 0.041), while HRV became more pronounced in several measures: RMSSD (53 ± 28 vs. 64 ± 32 ms, p = 0.033), DFAα1 (1.20 ± 0.25 vs. 1.06 ± 0.28, p = 0.005), HF (1192 ± 1290 vs. 1753 ± 1592 ms2, p = 0.025). CONCLUSIONS: Heart rate variability during SSX was not correlated with HRV at rest and did not change with training. Marathon training decreased HR and increased HRV at rest, as indicated with higher RMSSD and HF, and lower DFAα1 values.