I was at spanish banks this morning (8am with tide at perfection) and did some skimboarding. This is an amazing cardiovascular workout where you can fully utilize your entire body. You have to throw the board and run after it jump on and twist your body around while holding on( almost a mix of skateboarding and snowboarding on water), doing tricks etc. You are engaging so much core which is maybe why the majority of people out on the beach skimming are in pretty good shape. It doesn't matter if you are an expert or first timer because you are sure to get a great workout and the best part is it's alot of fun. Mix up your routine and try it out.