Wiktionary
tone up
vb. 1 To cause to give a higher tone or sound; to give a higher tone to; to make more intense; to heighten; to strengthen. 2 To firm and strengthen the muscles of the body by regular exercise.
WordNet
tone up
v. give a healthy elasticity to; "Let's tone our muscles" [syn: tone, strengthen]
Usage examples of "tone up".
He could tone up and sweat off some weight while keeping an eye on things.
Even in my college classes, close to 75% of 18 to 22-year-olds want to lose some weight or to tone up.
Why, it will be just the story to tone up that alleged page of society news you hand out in the Sunday Star.
Someone had once told her that Thek created novas to tone up their inner cores.
What I needed was a little touch of action to tone up my drooping nerve aids and accelerate my sluggish blood.