How should it change over time, and how can your friend track changes in muscular endurance?

Over time muscular endurance will improve if you are progressively training- getting harder. you could measure this by seeing how many push ups you can do to exhaustion and recording the result down each week. if the performer has been training they should be able to do more push ups   

One health risk and the most important one is obesity, it can cause obesity since you are not leveling your food like you wont ever get full because your just snacking between foods which can also cause diabetes.hope this : )

What are the following? i would expect him to get check-ups often.