A Pandemic within the Pandemic? Physical Activity Levels Substantially Decreased in Countries Affected by COVID-19 - Wilke, Jan; Mohr, Lisa; Tenforde, Adam S.; Edouard, Pascal; Fossati, Chiara; Gonzalez-Gross, Marcela; Sanchez Ramirez, Celso; Laino, Fernando; Tan, Benedict; Pillay, Julian David; Pigozzi, Fabio; Jimenez-Pavon, David; et al. (International Journal Of Environmental Research And Public Health, 2021)