The human head weighs 5kg. This weight keeps the neck toned and strong. In zero gravity on extended missions how do astronauts maintain muscle and bone strength in their necks? What type of neck exercises do they perform?
This exercise machine is a real orbital gym in miniature. Here you can twist the pedals of the bike, and do exercises for the back and neck. All this is not just physical education. Doctors call regular exercises - prevention, and astronauts call - a return ticket to Earth. Without such loads in long flights, the bones quickly lose calcium and become soft, and the muscles atrophy.
I don't know what exercises are used by astronauts to train their neck muscles. But there are some exercises here that will work in microgravity too.
Neck muscles will work against the arm muscles instead of gravity.
Isometric Exercises for Strengthening Your Neck Muscles
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The Ohio State University Medical Center