Free radical reactions are recognized as important mechanisms involved in potentially destructive biological processes. However to date, the majority of published literature has focused on examining free radical-mediated lipid peroxidation as opposed to the quantification of free radical species. Electron spin resonance spectroscopy has the ability to detect paramagnetic oxidants of a low concentration in biological systems, and is arguably the most sensitive, specific and direct method of measuring free radicals, but is under-utilised in exercise and medicine. This book will endeavour to examine the link between exercise, free radicals and antioxidants in health and disease. More specifically, the innovative technique of electron spin resonance spectroscopy in conjunction with molecular spin trapping will highlight the extent that exercise and diabetes mellitus per se generates oxidative stress. The latter section of this book will examine the efficacy of antioxidant supplementation in exercise and diabetes mellitus.