While both cycling and running can strengthen your core muscles, running has the advantage of burning more calories in a shorter period, leading to faster fat loss. As a result, the visible toning of your core muscles may be more pronounced with running. That said, both forms of exercise can be effective for improving your core strength. Running and cycling both require the engagement of your core muscles to maintain proper form and stability. By focusing on keeping your core muscles engaged and strong, you can maximize the benefits of either activity and improve your overall fitness level.