The association between depression symptoms, psychological burden caused by Covid-19 and physical activity: An investigation in Germany, Italy, Russia, and Spain - Brailovskaia, J.; Cosci, F.; Mansueto, G.; Miragall, M.; Herrero, R.; Bañosc, R. M.; Krasavtseva, Y.; Kochetkov, Y.; Margraf, J. (Psychiatry Research, 2020)