I don't know if you can control how much energy you have throughout the day. Perhaps with more exercise you can increase it somewhat, but there is always a limit. The best way to deal with this is to recognize when you have the most energy and do your most important work during that time. I personally have the most energy in the morning. So I block off my calendar before 1 PM and tell people not to invite me to meetings then. I try to have all my meetings in the afternoon, which for me doesn't take as much energy and focus. In the morning I then do my highest intensity, highest focus work. For me this is writing code. For a CEO I'm not sure but probably something like thinking through the vision and strategy of the company.