Intensity- and Dose-Dependent Differences in Heart Rate Variability Following an Acute Bout of Aerobic Exercise

Aerobic exercise requires a redistribution of blood flow to active tissue. The autonomic nervous system contributes to this redistribution of blood flow, which could impact heart rate variability (HRV) following exercise. However, little is known about the impact of exercise intensity and dose on post exercise HRV. The purpose of this study was to investigate HRV following aerobic exercise at different intensities and doses. We hypothesized that higher intensities and doses are associated with lower HRV values following exercise. To address this, 10 recreationally active young adults (5 females, 4 males, age = 28 ± 5 years, BMI = 23.06 ± 2.11 kg/m 2 ) completed a maximal oxygen uptake (VO 2 max) treadmill test and 3 experimental study days in randomized order where they exercised at 1) 30% VO 2 max for 30 minutes (30 EX), 2) 70% VO 2 max for 30 minutes (70 EX), and 3) 70% VO 2 max for a duration that resulted in energy expenditure equal to the 30 EX visit (70 EX EE ). Participants were instrumented with a 3-lead electrocardiogram (ECG) and HRV was measured at 25 minutes and 45 minutes post exercise for all study days. HRV was quantified as the root mean square of successive differences (RMSSD), high frequency (HF) power, low frequency (LF) power, the ratio of LF to HF (LF/HF), and the standard deviation of RR intervals (SDRR). During the post exercise period, heart rate (HR) differed by condition and time (time: P = 0.01, condition: P < 0.01, interaction: P < 0.01) such that HR was lower after 30 EX at both 25 minutes (55 ± 6 bpm) and 45 minutes (57 ± 9 bpm) compared to 70 EX (25 minutes = 73 ± 7 bpm, 45 minutes = 69 ± 4 bpm; P < 0.01 for both). At 25 minutes, HR was lower after 30 EX (55 ± 6 bpm) than 70 EX EE (67 ± 9 bpm; P < 0.01). Post exercise RMSSD differed by condition (time: P = 0.13, condition: P < 0.01, interaction: P < 0.01) such that RMSSD was lower 25 minutes after 70 EX (38 ± 19 ms) compared with 30 EX (95 ± 32 ms; P < 0.01). RMSSD was also lower 45 minutes after 70 EX (41 ± 12 ms) compared with 30 EX (66 ± 23 ms; P ≤ 0.05). RMSSD was lower 25 minutes after 70 EX EE (38 ± 19 ms) compared with 30 EX (95 ± 32 ms, P < 0.05). Post exercise HF power differed by condition and time (time: P < 0.05, condition: P < 0.01, interaction: P = 0.53) such that at 25 min, HF power was lower after 70 EX (893 ± 1300 ms 2 ) compared with 30 EX (4119 ± 2288 ms 2 ; P < 0.01), as well as 70 EX EE (1380 ± 1833 ms 2 ) compared with 30 EX (4119 ± 2288 ms 2 ; P < 0.01). The effect of exercise on SDRR differed by condition and time (time: P < 0.01, condition: P < 0.01, interaction: P = 0.53) such that at 25 min, SDRR was lower after 70 EX (47 ± 22 ms) compared with 30 EX (83 ± 26 ms; P < 0.01), as well as 70 EX EE (50 ± 22 ms) compared with 30 EX (83 ± 26 ms; P < 0.01). There were no differences between study days for post exercise LF or LF/HF ratio (P > 0.05 for all). There were also no differences between 70 EX and 70 EX EE for any measure of HR or HRV (P > 0.05 for all). These results indicate that exercise intensity can independently, and in combination with dose, affect HR and HRV after exercise. Specifically, higher intensity exercise resulted in higher HR and lower HRV 25 minutes after exercise. However, at 45 minutes post exercise, there were dose and intensity interactions only on RMSSD and HR. This implies that intensity is more impactful than dose on HR and HRV following exercise, and that some effects may resolve within 45 minutes of exercise. Funding: Wisconsin Alumni Research Foundation, NIH HL118154 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.