OBJECTIVE: To investigate the effectiveness of walking/running, cycling, or swimming for treating or preventing nonspecific low back pain (LBP). DESIGN: Intervention systematic review. LITERATURE SEARCH: Five databases were searched to April 2021. STUDY SELECTION CRITERIA: Randomized controlled trials evaluating walking/running, cycling, or swimming to treat or prevent LBP were included. DATA SYNTHESIS: We calculated standardized mean differences (SMDs) and 95% confidence intervals (CIs). Certainty of evidence was evaluated with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. RESULTS: No trials assessed LBP prevention or addressed acute LBP. Nineteen trials (2362 participants) assessed treatment of chronic/recurrent LBP. Low-certainty evidence suggests that walking/running was less effective than alternate interventions in reducing pain in the short term (8 trials; SMD, 0.81; 95% CI: 0.28, 1.34) and medium term (5 trials; SMD, 0.80; 95% CI: 0.10, 1.49). High-certainty evidence suggests that walking/running was less effective than alternate interventions at reducing disability in the short term (8 trials; SMD, 0.22; 95% CI: 0.06, 0.38) and medium term (4 trials; SMD, 0.28; 95% CI: 0.05, 0.51). There was high-certainty evidence of a small effect in favor of walking/running compared to minimal/no intervention for reducing pain in the short term (10 trials; SMD, -0.23; 95% CI: -0.35, -0.10) and medium term (6 trials; SMD, -0.26; 95% CI: -0.40, -0.13) and disability in the short term (7 trials; SMD, -0.19; 95% CI: -0.33, -0.06). Scarcity of trials meant few conclusions could be drawn regarding cycling and swimming. CONCLUSION: Although less effective than alternate interventions, walking/running was slightly more effective than minimal/no intervention for treating chronic/recurrent LBP. J Orthop Sports Phys Ther 2022;52(2):85-99. Epub 16 Nov 2021. doi:10.2519/jospt.2022.10612.