Huntington's disease (HD) is an incurable and fatal disorder characterised by progressive degeneration of the basal ganglia and the cerebral cortex. Contrary to earlier thinking, HD is associated with abnormalities in peripheral tissues which might even contribute to brain pathology including muscle wasting, mitochondrial abnormalities, and impaired muscle energy metabolism. Mitochondrial impairment and muscle atrophy in human HD patients and murine models of HD are associated with altered expression of PGC-1a, a transcriptional cofactor that seems to regulate many, if not all of the adaptations of muscle fibres to chronic endurance training, and induces improved exercise performance and increased peak oxygen uptake. We aim at investigating whether endurance exercise has the capability of stabilizing and / or reversing PGC-1a dependent alterations of muscle function and structure in HD patients, and whether muscle training ameliorates musculoskeletal and cardiovascular function, as well as motor and cognitive symptoms in HD patients.