We aim investigating whether endurance exercise has the capability of stabilizing and / or reversing PGC-1α dependent decline of muscle function and structure in HD patients, and whether muscle training ameliorates muscular and cardiovascular function, as well as coordination and cognitive decline in HD. To this end, we will train 20 male HD patients using a 6 months progressive endurance exercise program. In order to compare the size effect of exercise between HD patients and healthy individuals, 20 age-matched healthy males will perform the identical exercise regimen as HD patients. Within one week before the training period starts and within one week after it has ended, we will assess metabolic and functional data. In addition, we will analyze muscle tissue samples for muscle fiber structure, metabolic phenotype and cellular pathology. Finally, gene and protein expression analyses will be performed on muscle tissue extracts to gain insights into the molecular regulation of training adaptations in HD.