When muscles are exercised often and properly, they keep the arms firm and sinewy.

如果能经常正确地锻炼肌肉的话，双臂就会一直结实而强健。

youdao

I have evolved my own exercises, for the muscles I wish to keep firm, and I know they are right for me because I can feel them putting the proper muscles into play as I exercise.

我知道这是适合我的方法，因为当我运动的时候，我能感觉到它把我想要的部位运动起来。

youdao