School of Sport and Exercise Sciences, University of Kent, UK. Department of Paediatrics, University of Alberta, Edmonton, Canada. Department of Nutrition, Exercise and Sports, University of Copenhagen, August Krogh 2nd Floor, Universitetsparken 13, Copenhagen DK-2100, Denmark; Department of Respiratory Medicine, Bispebjerg University Hospital, Copenhagen, Denmark. Electronic address: mhostrup@nexs.ku.dk.