flex

1. V-T If you flex your muscles or parts of your body, you bend, move, or stretch them for a short time in order to exercise them. 屈伸 (肌肉或身体某部分)

He slowly flexed his muscles and tried to stand. 他缓慢地活动了一下肌肉，想站起来。

2. N-VAR A flex is an electric cable containing two or more wires that is connected to an electrical appliance. (电器用的) 花线[英国英语]

3. to flex your muscles→see muscle