Answer:
In any event, when someone has bitten off more than he can chew, he has promised himself or others to do a task that cannot be completed. The origin of the phrase itself comes from the act of putting too much food in your mouth at one time and not being able to chew it properly.
Step-by-step explanation:
The meaning of the sentence is that Alex tried too hard and attempted to lift something that he physically was not able to.