This study assessed the reliability of pulse rate variability (PRV) from wrist worn photoplethysmography (PPG) as a substitute for heart rate variability (HRV) measured via electrocardiography (ECG), across tasks with varying loads and ambulation. Twenty-four healthy adults completed 13 sensorimotor tasks before and after a cognitive fatigue protocol. HRV and PRV were calculated using time domain metrics from filtered ECG and PPG signals. Results showed poor agreement between PRV and HRV in all tasks, with significant differences in 11 of 13 conditions. These findings highlight the limitations of PRV from wrist worn devices as a substitute for ECG based HRV in real world assessments of cardiac variability. Future work should focus on better noise reduction techniques, improved sensor placement, and longer recordings to support spectral analysis, as well as larger sample sizes to clarify when PRV can reliably approximate HRV.
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