Yogi: I feel tired being aware of the 5 physical objects after a day.
Sayadaw: If you get tired, then something is not right with the practice. So, don’t follow any particular object; rather, stay with the awareness. Then, you use less energy. You can know the awareness, right?
So, don’t follow any object; seeing the process (follow the awareness) is good enough.
So, your only object is the awareness.