NASA astronauts who return from long ISS missions complete a 45 day rehabilitation program that consists of three phases.
After regaining some of their strength, flexibility and their ability to walk during phase one, the astronauts move onto phase two, which adds proprioceptive exercises and cardio reconditioning.
Proprioceptive exercises strengthen the body and improve the mind's perception of its movement and position.
Phase three, the longest phase, focuses on returning the astronaut to their optimal level of physical performance through functional development training.
Most astronauts return to their re-mission fitness level after the 45 days, according to NASA.