Roger Bartlett is Professor of Sports Biomechanics in the School of Physical Education, University of Otago, New Zealand. He is an Invited Fellow of the International Society of Biomechanics in Sports and an Honorary Fellow of the British Association of Sport and Exercise Sciences, of which he was Chairman from 1991-4.Chris Gratton is Professor of Sports Economics and Director of the Sport Industry Research Centre at Sheffield Hallam University, UK.Christer Rolf is Professor of Sports Medicine, Consultant Orthopaedic Surgeon and Executive Director, Sheffield Centre of Sports Medicine, University of Sheffield, UK.