It strengthens the upper body. When you paddle on your surfboard, you exercise your shoulders and upper back. When you reach for that bomb of a wave coming at you, your triceps, biceps, deltoids, and core muscles (trapezius, rectus abdominis, latissimus dorsi, and obliques) all kick in. All of this activity helps build muscle mass and strength. Surfing also requires you to control a board that is at least 38 inches wide. This involves using your arms and hands for balance as you paddle out into the ocean. The more you surf, the better you get at it. So, over time, you will find that you can do more intricate maneuvers with your board while keeping your balance. This will help strengthen your arms, chest, and back. Finally, surfing is an outdoor sport that requires you to be in good physical condition. You need strong legs, glutes, abs, chest, and arm muscles to stand up under the heavy load of the ocean when it dumps its water onto the shore. The more you surf, the more exercise you get. This means that surfing is a great way to stay in shape. It's fun, too!