Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by expansion of a translated CAG repeat in Ataxin-1 (ATXN1). To determine the long-term effects of exercise, we implemented a mild exercise regimen in a mouse model of SCA1 and found a considerable improvement in survival accompanied by up-regulation of epidermal growth factor and consequential down-regulation of Capicua, which is an ATXN1 interactor. Offspring of Capicua mutant mice bred to SCA1 mice showed significant improvement of all disease phenotypes. Although polyglutamine-expanded Atxn1 caused some loss of Capicua function, further reduction of Capicua levels--either genetically or by exercise--mitigated the disease phenotypes by dampening the toxic gain of function. Thus, exercise might have long-term beneficial effects in other ataxias and neurodegenerative diseases.