Changes in nocturnal heart rate variability and endurance performance during a high-intensity or high-volume endurance training period in recreational endurance runners

Abstract

It is known that endurance training affects the modulation of the autonomic nervous system and heart rate variability (HRV). As a method HRV may be a potential tool to monitor trainability and endurance training adaptation. The purpose of this study was to examine changes in nocturnal HRV indices and endurance running performance during high intensity versus high volume endurance training. In total, 28 recreational male and female endurance runners (35 ± 8 year, VO2max 50 ± 5 ml/kg/min) were matched into two training groups after the 8 week basic training period (BTP) according to HRV, endurance performance and training adaptation during BTP. During the 8 week hard training period (HTP), the high intensity training (HIT) group (n=14) increased training intensity and the high volume training (HVT) group (n=14) increased training volume from level of BTP. Basal nocturnal HRV indices (RMSSD, SDNN, LFP, HFP, TP) and endurance running performance were measured at baseline, after BTP and HTP. In the HIT group, VO2max (3.7 %, p=0.005) and Vpeak (2.4 %, p=0.002) improved significantly during HTP, whereas no changes were observed in the HVT group. Similarly, nocturnal HRV indices (RMSSD: 11.6 %, p=0.034; SDNN: 11.4 %, p=0.005; TP: 2.4 %, p=0.040) increased only in the HIT group but not in the HVT group. Significant correlations were observed between endurance training adaptation and changes in nocturnal HRV indices (∆VO2max, ∆TP: r=0.54, p=0.045 and ∆Vpeak, ∆SDNN: r=0.55, p=0.050) in the HIT group. This study showed that high intensity endurance training induced greater chang-es in nocturnal HRV indices and endurance running performance compared with high volume training. In order to lead significant changes in nocturnal HRV indices among recreational endurance runners high intensity endurance training seems to be needed. Finally, the present findings support the suggestion of HRV as a monitoring tool of endurance training adaptation.