However, evidence, primarily from the adjuvant setting, that physical activity impacts on treatment tolerability and tumor progression is a strong enough rationale to now embark on this prospective trial. By assessing in a large randomized controlled trial whether a 12-week structured physical activity program during chemotherapy in patients with newly diagnosed colorectal cancer undergoing standard first-line chemotherapy improves progression-free survival as compared to standard first-line chemotherapy alone, all pre-requisites for a practice-changing intervention are met.