In past spaceflights, astronauts have lost approximately 1% of their bone mass per month due to disuse atrophy. In a process called remodeling, bones are constantly broken down and rebuilt through osteoblasts and osteoclasts. In microgravity, this process is thrown off balance, resulting in localized bone mass loss. Disuse atrophy is very similar to osteoporosis, and growth hormones, sex hormones, and exercise have proven to slow down osteoporosis on Earth (NASA). A rigorous exercise plan on Earth followed by resistance training while in microgravity could slow the effects of disuse atrophy. In recent studies at Columbia University, researchers discovered that when serotonin production is slowed, bone loss is also slowed. A therapy that was developed was not only able to stop osteoporosis in the rodents it was tested in, but also able to reverse the process (Columbia University, 2010). Before long duration spaceflights are planned, the consequences on the human body must be taken into account. Research and development to create a medicine help maintain healthy bones must be funded. Such studies create remedies for astronauts in microgravity and also lead to spin-off medicines for osteoporosis patients on Earth. The impact of microgravity on the skeletal system could lead to dire consequences for long space flights as normal body functions slowly shut down.
Certain muscles in the human body are called antigravity muscles. These muscles, for example the calf, back, and neck muscles, help support the body against the force of gravity. In a flight lasting only 5-7 days, astronauts can lose up to 20% of their muscle mass (Canadian Space Agency). Reduced protein synthesis leads to atrophy, and contractile proteins are lost. Furthermore, actin thin filaments and myosin thick filaments become disproportional in muscles (Fitts, 2000). Hours of exercise every day to counteract this process would be time consuming for an astronaut’s busy schedule, and possible strategies to help build muscle have been tested. One procedure is the Percutaneous Electrical Muscle Stimulator (PEMS), which sends pulses into muscles, causing them to contract (ESA, 2000). The PEMS can accompany exercise aboard the spacecraft to keep astronauts’ muscular systems strong. Traditional exercise should not be forgotten, however, and daily workouts with resistance elastic bands and stationary bikes or rowing machines would also be used.
