1. UCLA Exercise Physiology Research Laboratory, Department of Medicine, David Geffen School of Medicine; University of California; 10833 Le Conte Avenue, 37-131 CHS Los Angeles 90095 USA
2. Department of Physiology, David Geffen School of Medicine; University of California; Los Angeles USA
3. Department of Neurology, David Geffen School of Medicine; University of California; Los Angeles USA
4. Cambridge University Sports & Exercise Medicine Unit, Addenbrooke's Hospital; Cambridge England
5. Queen's University; Belfast Northern Ireland UK