There are plenty of high intensity activities with low risk of injury. Rowing and swimming come to mind. I think the bigger problem is that, as far as I can te

There are plenty of high intensity activities with low risk of injury. Rowing and swimming come to mind. I think the bigger problem is that, as far as I can tell, very few people have the appropriate personality type for high intensity exercise. Most people seem to experience it just as pointless discomfort.