1 Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Netherlands; Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Belgium. Electronic address: W.Back@uu.nl.
2 Department of Human Movement Sciences, Vrije Universiteit Amsterdam, Netherlands; Faculty of Sports and Nutrition, Amsterdam University of Applied Sciences, Netherlands. Electronic address: M.Hofmijster@vu.nl.