Sunita Williams & Butch Wilmore face gravity struggles after space return.
Astronauts set to return to Earth on March 19 after being stranded.
Gravity will feel harsh, making even lifting a pencil feel exhausting.
Cartilage damage is a concern due to reduced movement in space.
Jumping exercises may help astronauts strengthen their cartilage.
Williams will undergo rehab to regain strength & bone density.
Despite challenges, both astronauts are excited to return home!