There’s a real analogy between looking after your teeth and your back.
We know with our teeth we need to brush our teeth gently and regularly twice or three times a day. The dentist doesn’t say “no no, you don’t need to brush every day; on a Sunday do 35 vigorous minutes of brushing your teeth, that’ll do it”
That’s similar to exercise for the back. We need to exercise our back gently and regularly. And as sugar is bad for the teeth, sitting is bad for the back.