Seen a surfer’s body lately? They got those great muscles by using their calves, thighs and upper body to maintain balance while surfing. uSurfâ„¢ is designed to simulate the motions of surfing, and to shape and tone targeted muscle groups. The wave-action deck of uSurf rocks both back and forth and side to side. As you ride, your body automatically engages your calves, thighs, hips, and seat. Leaning back and forth also engages abs, obliques, and back muscles.