Abstract-Periodic motion artifacts affect photoplethysmography (PPG) signals in activities of daily living (ADL), cardiopulmonary exercise testing (CPX), and cardiopulmonary resuscitation (CPR). This hampers measurement of inter-beat-intervals (IBIs) and oxygen saturation (SpO2). Our objective was to develop a generic algorithm to remove periodic motion artifacts, recovering artifact-reduced PPG signals for beat-to-beat analysis. Methods: The algorithm was retrospectively evaluated on forehead PPG signals measured while walking on a treadmill. The step rate was tracked in a motion reference signal via a secondorder generalized-integrator with a frequency-locked loop. Two reference signals were compared: sensor motion relative to the skin (∆x[n]) measured via self-mixing interferometry, and head motion (av[n]) measured via accelerometry. The step rate was used in a quadrature harmonic model to estimate the artifacts. Quadrature components need only two coefficients per frequency leading to a short filter, and prevent undesired frequencyshifted components in the artifact estimate. Subtracting the estimate from the measured signal reduced the artifacts. Results: Compared to ∆x[n], av[n] had a better signal-to-noise ratio and more consistently contained a component at the step rate. Artifact reduction was effective for distinct step rate and pulse rate, since the artifact-reduced signals provided more stable IBI and SpO2 measurements. Conclusion: Accelerometry provided a more reliable motion reference signal. The proposed algorithm can be of significance for monitoring in ADL, CPX or CPR, by providing artifact-reduced PPG signals for improved IBI and SpO2 measurements during periodic motion.