Author(s): VALTONEN, R., YLINEN, V., HUIKURI, H., TULPPO, M., Institution: UNIVERSITY OF OULU, Country: FINLAND, Abstract-ID: 1826

INTRODUCTION:
Measurement of cardiac autonomic function, using heart rate variability (HRV) techniques, has become popular among users of wearable devices such as heart rate monitors, smart rings, and smartwatches. One application is to identify recovery status of cardiac autonomic regulation after exercise using vagally mediated short-term HRV measurements. However, the reproducibility of HRV after exercise is not well known. The aim of this study was to identify the reproducibility of heart rate, HRV and blood pressure (BP) before and after aerobic exercises and control measurement.
METHODS:
Eighteen participants (age 27±6, V02max 45±7 ml/kg/min, female n=8) performed an incremental maximal exercise test by bicycle ergometer until exhaustion. Thereafter, participants performed two aerobic sessions (60% of the maximal watts), 30 min each, and one 30 min control session without exercise in randomized order. Heart rate and vagally mediated high frequency power of RR intervals (HF; 0.15-0.4 Hz) were analyzed over 5 min at rest and 30 min after interventions. BP was measured 3 times in 2 min intervals and mean values were used at rest and during recovery. The reproducibility was assessed by the 95% confident interval (CI) of intraclass correlation coefficient at baseline and in recovery phase.
RESULTS:
Heart rate at rest and after interventions was 68±11 vs. 60±9 bpm, 68±11 vs. 72±10 bpm, and 66±11 vs. 70±10 bpm for control, exercise I and exercise II, respectively (time x group interaction p<0.001). Corresponding HF power at rest and after interventions was 6.51±1.68 vs. 6.71±1.36 ms2, 6.41±1.44 vs. 6.21±1.02 ms2, and 6.62±1.42 vs. 6.62±1.15 ms2 (time x group interaction p=ns), and systolic BP at rest and after interventions was 122±9 vs. 118±12 mmHg, 124±15 vs. 113±13 mmHg, and 123±12 vs. 113±12 mmHg (time x group interaction p<0.05). Reproducibility at rest was satisfactory for heart rate (95% CI 0.561-0.937), good for HF power (95% CI 0.643-0.949), and excellent for systolic BP (95% CI 0.810-0.975. Reproducibility after exercise was good for heart rate (95% CI 0.638-0.948), poor for HF power (95% CI 0.002-0.848), and excellent for systolic BP (95% CI 0.812-0.974).
CONCLUSION:
Heart rate was still elevated 30 min after exercise compared to control condition and reproducibility was satisfactory at rest and good after exercise. Despite elevated heart rate, mean HF power values recovered to the baseline level 30 min after exercise and reproducibility of HF power was good at rest but poor after exercise. Finally, reduced systolic BP was obvious after exercise and reproducibility of systolic BP was excellent at rest and after aerobic exercise.