Integrating Astronomical Seasonal Phase into Physical Activity Research

Seasonal phase variation, characterized as a sinusoidal waveform anchored at the annual solstices, can be positively associated with both between- and within-person differences in physical activity in observational, longitudinal, and experimental studies. A continuous measure for adjusting seasonal phase variation will reduce seasonal confounding in physical activity research, increase the precision of effect sizes, and improve the reproducibility of findings. Summary: A continuous measure of astronomical seasonal phase is proposed to advance observational, longitudinal, and experimental research on physical activity.