Or ... He exercises every morning, so that he can keep healthy. The second is literal translation, which is not as good as the first.
2. How do you keep healthy?
In order to keep healthy, you should go on a diet and do some exercise. Foreigners seldom use imperative mood must, but they often use suggestive should.
I run five kilometers every day to keep healthy.
We must do enough exercise to keep healthy. It's different here. The subject has changed. This is an objective fact. Just contact me with must ~ if you are not satisfied, I hope it will help.