This study will examine the role of temperature in modulating aspects of energy metabolism in human skeletal muscle. Tests will be conducted at rest and during concentric dorsiflexion exercise of the Tibialis anterior (TA) muscle using an existing custom-designed dynamometer in conjunction with mild local heating and cooling. Magnetic resonance spectroscopy (MRS), performed in a 4-tesla whole-body NMR system, will be used to non-invasively measure muscle temperature and energy-state. Specifically these tests will assess the extent to which temperature changes occur during aerobic exercise and how small temperature changes affect mitochondrial function in-vivo.