Effects of natural between-days variation in sleep on elite athletes` psychomotor vigilance and sport-specific measures of performance - Knufinke, M.; Nieuwenhuys, A.; Maase, K.; Moen, M. H.; Geurts, S. A. E.; Coenen, A. M. L.; Kompier, M. A. J. (Journal of Sports Science & Medicine, 2018)