Many people start swimming with fins and are initially surprised by the pain in their feet and ankles. Ankle mobility is the root cause of pain when it comes to swimming with fins, which requires both practice and stretching. It typically takes 3-4 weeks to feel like you can finish a swim with fins workout without such discomfort in the feet and ankles. This is one of several reasons we recommend adding mobility training to your workouts. You can do this swim workout any day of the week.