Heart rate variability versus visual analog scale for objective and subjective mental fatigue detection: A randomized controlled trial

Fatigue is a multidimensional phenomenon. Although psychological tests can be used to evaluate subjective fatigue, an objective measurement of fatigue is needed to evaluate mental, physical, and occupational health and inform appropriate interventions. Heart rate variability (HRV) has emerged as a potential candidate for assessing objective mental fatigue; however, its effectiveness and safety remain inconclusive. To address these, we conducted a single-center, randomized trial to compare the efficacy and safety of HRV with subjective psychological tests for evaluating mental fatigue. Participants aged 20 to 65 years who had received annual health check-ups and had been found to have no health concerns were included in this study. We compared HRV indexes after performing a calculation task with a control group that rested. The primary outcomes were HRV indexes as recorded by wearable electrocardiography after an intervention consisting of a calculation task. Subjective measures (visual analog scale [VAS] for fatigue and Profile of Mood States 2nd Edition [POMS2]) were evaluated as secondary outcomes. One hundred forty participants were randomized into a calculation task and control groups. Participants who performed the calculation task had a lower square root of the mean squared differences between successive RR intervals (RMSSD), absolute power in the high-frequency band, and standard deviation of Poincaré plot. In psychological tests, participants who performed the calculation task demonstrated significantly higher scores on the VAS for fatigue and POMS2. Multiple comparisons of RMSSD from HRV indexes, VAS for fatigue, and total mood disturbance from POMS2 revealed that RMSSD and VAS for fatigue were significant indicators associated with the calculation task. On the other hand, the vectors of HRV indexes and psychological tests differed based on primary component analysis. We identified RMSSD, an objective index, and VAS for fatigue, a subjective index, as significantly related to mental fatigue.