weak bones when in a wheelchair?

Question

why do people in wheelchairs with paralyzed lower limbs have thin weak bones in their thighs and legs

Answer 1

Because you have to apply weight and pressure to bones to keep them strong... That's why weight lifting will increase your bone density... people who have lost their teeth get bone resorbtion in the bony ridge in the jaw so their dentures don't fit right, etc.

Bones need to be flexed and pressured and pushed to stay strong. Use it or lose it basically...