Student or Learner
Please set me clear on the following in red.
On workout intensity, Jack LaLanne explained how, as people get older, they still need to give it all they've got. The writer for <USA Today> asked for clarification, "Don't doctors tell senior citizens not to push it too hard?" to which Jack barked, "What the hell do they know about exercise? Most of them know zero! You gotta push elderly people to muscle failure like everyone else. That's the only way the body responds."
Jack was 86 at the time, 50 years my senior, and still tearing up the gym every day. I remember thinking how I'd be happy to just be able to to get out and walk on the beach when I reach that age.
Especially, what does "muscle failure" mean? And I don't know what "tearing up" means in the context. Does it mean "exercise hard in the gym"?