Aerobic exercise is a vital treatment for people living with Parkinson’s disease. Although anti-parkinsonian medication helps alleviate Parkinson’s symptoms, it is not known to slow the rate of disease progression. Aerobic exercise is a treatment with the most compelling evidence for its potential to slow Parkinson's disease progression. While both moderate- and high-intensity aerobic exercise provide health benefits, it is currently unclear which intensity is more effective for people with Parkinson’s. The SPARX3 (NCT04284436) study is the first randomized control trial designed to investigate the effects of moderate- and high-intensity aerobic exercise on disease progression in untreated patients with Parkinson’s.