Factors Associated With Longitudinal Psychological and Physiological Stress in Health Care Workers During the COVID-19 Pandemic: Observational Study Using Apple Watch Data - Robert P Hirten; Matteo Danieletto; Lewis Tomalin; Katie Hyewon Choi; Micol Zweig; Eddye Golden; Sparshdeep Kaur; Drew Helmus; Anthony Biello; Renata Pyzik; Claudia Calcagno; Robert Freeman; et al. (Journal of Medical Internet Research, 2021)