Body surfing:
Body surfing works every muscle in your body. Walking through waist-deep water, diving under the waves, maintaining your position and then catching waves makes for a great workout.
Ocean swimming:
Ocean swimming is highly aerobic, and it's low-impact. Plus, it's great for your back because your stomach muscles are doing so much of the work
Surfing:
As well as building upper- and lower-body strength, surfing builds stamina and is great cardio. It works almost every muscle in your body. If you ride 20 waves, you've done 20 pushups.
Soft-sand running:
Running on sand is physically more demanding than running on a hard surface, but less stressful because of the greater shock absorption.
