hit the wall idiom
（奔跑、运动、比赛期间疲倦到无法继续）遭遇极点
to reach a point when you are running, exercising, playing sports, etc. where you are so physically tired you feel you cannot continue
Many marathon runners hit the wall at around 20 miles. 许多跑马拉松的人在20英里左右会遭遇极点。