For many human movements, the relation between intensity and injury is a u-curve with high risk at extremely low intensity (atrophy) and extremely high intensity (overuse/repetitive strain), and low risk at moderate intensity.

It's not so much the time as the toughness over time.

Have a steak or dense bread to exercise your jaws.

Or maybe beef jerky?

> We can't win, can we?

"All day": There's your problem.