Heart rate variability during repetitive work in the presence of fatigue

Abstract: Fatigue has been demonstrated to have a direct negative effect on the productivity of the worker and a marked rise in the long-term occupational risk. The measures being presently applied mainly target the muscular activity directly, that together with subjective understandings of one’s own fatigue levels make up an inaccurate cumulative evaluation of fatigue. “Industry 4.0” wearable devices allows for a more complete and continuous measurement of variables related to fatigue, and thus represent a more accurate value of the worker’s fatigue level.Aim: To analyse the structure of heart rate variability, as a measure of cardiovascular responsiveness, during repetitive work when muscular fatigue is present. Tasks: A protocol was developed to simulate a real-life workplace scenario with a set of low-intensity repetitive tasks that are commonly practiced. The signals obtained were then processed, and heart rate variability was calculated using multifractal analysis and frequency domain variables.Hypothesis: It was hypothesized that the structure of variability will change during repetitive work in the presence of fatigue.Methodology: Participants were asked to perform three 10-minute trials of a repetitive task involving a specific set of movements commonly required for work. Between each trial, a fatigue protocol was carried out, targeting the main agonist muscle. An ECG was collected through a wearable band placed on the level of the xiphoid appendix during the three trials denominated: Baseline, Fatigue 1, and Fatigue 2. Results: Significant differences were found in Very Low Frequency and Low Frequency in the Baseline and Fatigue 2 conditions. However, there were no significant differences in High Frequency. The results of the fractal analysis did not show any significant differences for any q-order, indicating that the fractal of HRV is maintained.Conclusions: These results are enthusiastic for applying algorithms that use heart rate variability to quantify cardiovascular responsiveness to fatigue during repetitive work. These results suggest that fatigue alters the variability structure of HRV, but the fractal structure of HRV remains unchanged.

Keywords: ECG, Fatigue, Heart rate variability, Occupational risk, Work, Industry 4.0, Operator 4.0

DOI: 10.54941/ahfe1003433

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