Nowadays, the public emphasis exercise, especially aerobic exercise, can make us healthier. Exercise should be good to health, but I think exercise should be treated carefully or exercise is not good for health.
First, it is common to be injured due to exercise. It is very common to hear that some famous football player or basketball player are injured and cannot play in that season. Some injury cannot be totally recovered. The Athlete may feel painful when they get old and on a rainy day. Injury certainly violate the standard of being healthy. Moreover, there is even a research claims that chlorine in swimming pool may cause cancer.
Second, the performance of exercise are based on physical and biological rules, but not way to make us healthy. For those who play sports, they usually not only want to be healthy, but also want to win in a competition. For example, the pose of fencing seems not natural as they need to turn their head and walk like a crap. For track and field, athlete need to follow exactly what the performance required and train for a specific muscle.
I am not saying that we should not exercise, but we need to exercise in the safe way and choose the exercise that do not harm our health.