A systematic review of nine randomized controlled trials (14 comparisons) examined how MRI-measured articular cartilage responds to exercise in people with knee osteoarthritis (OA). Key findings The review found that exercise did not harm cartilage in the following OA groups: At-risk populations: No effect on cartilage defects was observed. One comparison showed improved glycosaminoglycan (GAG) content. Established OA: Most comparisons showed no effect on cartilage thickness