Permanent muscle loss in zero-g

[GRB 080319B]

Why is there permanent muscle loss from space travel? Is this general muscle atrophy or specific to certain muscles (i.e., which muscles don't experience permanent atrophy and why)?

 

[Ryan_m_b]

Muscle loss isn't permanent. In free-fall muscles are not stimulated and so they begin to atrophy, you would see a similar effect if you lay down in bed for weeks on end.

In addition bone mass also decreases due to the lack of mechanical stimulus.

 

[ViewsofMars]

Why is there permanent muscle loss from space travel? Is this general muscle atrophy or specific to certain muscles (i.e., which muscles don't experience permanent atrophy and why)?

The NATIONAL SPACE BIOMEDICAL RESEARCH INSTITUTE is an excellent place to explore:

The Body in Space

The human body is uniquely designed to live in Earth’s gravity. In space, the body begins to adapt to the microgravity environment.

NSBRI’s science and technology program is addressing ways to reduce or eliminate many of the changes to the body that impact an astronaut’s ability to perform well in space and that might impact their health after returning to Earth. The NSBRI program also looks at ways to enhance countermeasures already in place on long missions.

Here’s a quick introduction to how the body reacts to life in space [. . .]

Muscles
Extended spaceflight results in less load on the leg muscles and on the back’s muscles used for posture. As a result, the muscles can begin to weaken or atrophy, and this could lead to fall-related injuries and accidents during exploration missions. Astronauts currently exercise to help maintain their muscle mass, but nutritional interventions designed to reduce the muscle loss may one day be added as a complement to the exercise program.
[. . .]

Please read on . . .
http://www.nsbri.org/DISCOVERIES-FOR-SPACE-and-EARTH/The-Body-in-Space/