Tread water in deep end of pool, arms out to sides and legs extended beneath you. Engaging abs, squeeze legs together and sweep them backward, bending knees slightly, then quickly extend them forward (like a dolphin's tail); counterbalance motion by sweeping arms through water in opposite direction of legs. Continue for 1 minute. TRAINER TIP: Your whole body should crack like a whip; initiate the movement from your core, not your legs.

Source by rominarahimirza