When she hit, her brain went to jelly, and all her muscles failed.

Sooner or later Human muscles would fail to answer at some critical point.

There had been moments when muscle had failed, but never that.

Just before he reached the floor, however, the muscles of his right leg failed to respond.

The muscles are all failing, like a machine where every part quits at once.

He tried to push himself up, but the muscles of his arms failed and he collapsed.

The man squeezed another shot away, but his muscles were failing him and he slumped to the ground.

He tried to get up from the chair and found that his muscles were failing him.

He stumbled on the step, almost fell, but somehow his weakened muscles did not fail him.

He tried to set the chair down gently, but his muscles failed him and let it crash to the podium.