What? You thought they only spend a few minutes a day in the heavy gyms?
.9 standard is about .81 Earth gravity at sea level. Test load is an amount equal to 20% of the subject's body mass.
Orion medicals have the authority to order more time to counter bone and muscle degeneration. Peach and X are risking health problems by letting their duties keep them away. For this reason command staff spend a minimum of one full cycle recovering from interstellar missions (which is actually the only way the Expeditionary Corps can get anyone to take an HQ assignment).
Sky, for some reason, hasn't needed to set foot in a heavy gym since gaining access to an unlocked fabber, in spite of those heels she runs around in lately.