Cardiovascular Reactivity (CVR) During Repetitive Work in the Presence of Fatigue

Fatigue during repetitive tasks in the workplace has been intrinsically connected with occupational risk and a reduction in productivity. Currently, the measures taken are based on subjective interpretations of fatigue by the workers or on direct muscular activity, which then make up for a cumulative evaluation of fatigue. The concept of “Industry 4.0” wearable devices would allow a continuous monitoring and thus, a more realistic representation of their fatigue levels.Aim: To quantify heart rate variability, measuring cardiovascular responsiveness, during repetitive work when 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 fractal analysis and time domain variables. Hypothesis: It was hypothesized that 1) the amount of variability and 2) 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. Between each trial, a muscular fatigue protocol was carried out, targeting the main agonist muscle. An ECG was collected during the trials (Baseline, Fatigue 1, and Fatigue 2) through a wearable band placed on the level of the xiphoid appendix. Results: The nonlinearity of the heart rate variability showed no statistically significant changes, unlike the time domain measures that significantly differentiated the baseline trial from the fatigue trials, namely the Standard Deviation of NN intervals, the Root Mean Square of successive RR interval differences, Coefficient of Variation, and Heart Rate itself. Conclusions: These results are enthusiastic for applying algorithms that use heart rate variability to quantify cardiovascular responsiveness to fatigue during repetitive work. They show that with information in the time domain, it is possible to verify physiological changes that the worker is undergoing. Additionally, these changes are also related to the amount of variability and not to the fractal structure of heart rate variability.