Before revision: Only the bicycle ergometer was used on Skylab 2, the MK I and MK II “Mini Gym” exercisers were added for Skylab 3, and a passive “treadmill” was flown on Skylab 4.
After revision: Only the bicycle ergometer was used on Skylab 2, the MK I and MK II "Mini Gym" exercisers were added for Skylab 3, and a passive "treadmill" was flown on Skylab 4.