Exercise, specifically loading exercises like treadmill walking with bungee cords, is required to maintain bone and muscle health in microgravity.

“in space you don't load your skeleton by walking we heavily supplement vitamin d calcium there's those things you need to scaffold and build bone so the astronauts get get their vitamins and minerals and then like leland was saying two hours a day of exercise where we load people on the t2 treadmill”

Resistance exercise like lifting free weights is essential to prevent bone density loss and osteoporosis during long-duration space flight.

“when you go to space the morphology of your bone structure changes because there is no gravity well we're we're in free fall around the planet there was actually gravity nine what nine tenths of a g in 240 miles up but your bones start to change and when you come home if you haven't done resistive e”