Muscles are required for all of the movements we make. They become stronger when we work harder, and lose mass when we fall into inactivity. Unfortunately, in space, no matter how hard they are working, astronauts lose muscle mass. Weightlessness removes most all of the daily exercise that maintains the body’s musculoskeletal system. Even just standing on Earth involves constant effort – the muscles in the back of the leg must be constantly active to keep the body upright. Muscles are also needed to keep the spine straight and the head upright. In space, the control of movement shifts to the arms, hands and fingers, leaving the lower extremities with little exposure to activity.
As activity decreases, protein synthesis in the muscle fiber declines. This atrophy can occur rapidly when muscles are used at much lower rates than normal. With the addition of under-nutrition and stresses that are prone to occur in space, the loss of muscle can progress even more rapidly. A variety of environmental and biological factors converge to lessen muscle mass, making the response to spaceflight intrinsically individualized. While some individuals may find spaceflight more taxing, others may find it much more manageable.
The prime solution would be artificial gravity, which would simulate the activity required to perform tasks on Earth and properly exercise the muscular system. Currently, though, it is ineffective to simulate all of Earth gravity – one-third or one-sixth of Earth’s gravity, applied intermittently could be almost as effective. Research is still being done in this area.
The treatment plan for muscle loss must be tailored to the individual, a key point of Astro-Omics. Aerobic exercise, stretching, strength training and even electrical stimulation (which activates muscles and increases protein synthesis) can be used at different levels for different people. Also, interventions like antioxidants, growth hormone, growth factor, steroids, etc., could be effective in maintaining muscle mass. Even atrophy inhibitors could be used to block biochemical pathways involved in protein degradation. Also in the realm of Astro-Omics would be the individualized monitoring of weight, biochemical measurements, anthropometric measurements, and performance in functional tests and activity, which could guide exercise and nutritional prescriptions.