The Effects of Submaximal and Maximal Exercise on Heart Rate Variability

The purpose of this study was to examine heart rate variability (HRV) at rest, and during submaximal (100 bpm) and maximal exercise in collegiate distance runners. We predicted there would be less HRV during exercise. Eight collegiate runners (19-22 yrs) were recruited for participation. The participants were equipped with a standard Lead II EKG to record HRV at rest. The participants then performed an incremental VO_2max test while running on a treadmill. EKG was recorded throughout the exercise test and HRV was later calculated during the submaximal and maximal exercise. To assess HRV the standard deviation of R-R intervals (SDNN) was calculated at rest and during submaximal and maximal exercise. A one-way ANOVA was used to determine HRV differences between these three states. The average R-R interval was 0.961 ± 0.155 s (64 bpm), 0.413 ± 0.018 s (146 bpm), and 0.321 ± 0.008 s (187 bpm) for rest, submaximal, and maximal exercise, respectively. There were significant differences in SDNN from rest to submaximal (0.108 ± 0.055 to 0.008 ± 0.002 s, p < 0.05), and from rest to maximal exercise (0.108 ± 0.055 to 0.006 ± 0.002 s, p < 0.05). When comparing HRV between the resting and exercise states it seems that the parasympathetic nervous system (PNS) influence at rest contributes to greater HRV, whereas the sympathetic nervous system (SNS) influence during both submaximal and maximal exercise corresponds to a reduced HRV. These effects may be related to the enhanced automaticity effects of norepinephrine acting on its B₁ receptor sites in the heart.