When muscles are used to perform physical activity they must metabolise available fuel to generate energy for contraction. The harder a muscle must work, the more fuel is required. The relation between how hard muscles must work and their need for fuel is an area of intense interest in the study of human performance. In the past, intramuscular energy metabolism has been measured directly by muscle biopsies,¹ which are invasive. During the last two decades, the sophistication of magnetic resonance (MR) technology has steadily improved. Using magnetic resonance spectroscopy (MRS), it is now possible to detect non-invasively changes in a number of important intramuscular fuel sources, such as muscle glycogen,^2–5 during exercise and recovery. Magnetic resonance imaging (MRI) has been used for some time to examine anatomical effects of sport and training.⁶ Recently it has become possible to measure exercise induced physiological changes with MRI and use information from these measurements to determine muscle activity patterns.^7–9 These more recent advances open up a new range of possibilities to use MR technology not only as a diagnostic tool, as in the past, but in …