Effects of marathon training on heart rate variability during submaximal running: a comparison of analysis techniques

PurposeAssessment of heart rate variability (HRV) during exercise is an emerging area of study. Measurements of HRV are characterized by domain (time, frequency, and nonlinear) or time scale (short or long-term). The purpose of this study was to compare methods of HRV analysis during submaximal running before and after 18 weeks of marathon training.MethodsPre and post-training, 42 recreational runners (21.1 +/- 1.5 years, 28 f) completed a 2-mile (3218 m) time trial (2MI) and a submaximal run (SUBMAX) at 75% of 2MI speed. Changes in HRV during SUBMAX and physiological measures were assessed with paired samples t tests. Correlations between the changes of selected variables were assessed with Spearman's rho.ResultsLong-term measures of HRV did not change with training, while several short-term measures changed: Poincare plot SD1 (PPSD1) (2.9 +/- 0.9, 3.5 +/- 1.5; p = 0.049), PPSD1(.)PPSD2(-1) (0.23 +/- 0.11, 0.29 +/- 0.17; p = 0.047) and Detrended Fluctuation Analysis alpha 1 (0.95 +/- 0.25, 0.82 +/- 0.28; p = 0.006). Both 2MI (15.6 +/- 2.0 min, 14.2 +/- 1.7 min; p <= 0.001) and VO(2)max (50.6 +/- 7.6, 52.7 +/- 7.3; p = 0.049) improved with training. Change in sample entropy (SampEn) was correlated with change in 2MI (rho = - 0.379, p = 0.016), suggesting an association between this measure of HRV and endurance performance.ConclusionsMeasures of short-term HRV change with marathon training and may reflect adaptation independent of change in aerobic capacity.