The best way to strengthen back muscles is in a static position, You maintain the position of the core while moving other parts of the body.

They still think of the core as more of a static thing.

He had grown so fast and so tall. We had to strengthen his stomach muscles. He hasn't had a problem since.

I would see this as a game to strengthen his bargaining position in the party.

This is a corporate matter and we maintain the same position as before, which is that this is a matter for companies and shareholders to decide.

It should not strengthen the position of those with a preconceived notion about terrorists.