Sen—Living in microgravity has many consequences for the human body. Bone deterioration and muscle loss mean crew members aboard the International Space Station must excercise for 2 to 3 hours every day. Fluid redistribution triggers the body to excrete fluids, leading to dehydration. Decreased physical stress causes the heart to slow down and reduces the production of red cells causing "space anemia". Immune system and production of infection fighting cells is reduced. Prolonged weightlessness also causes blurred vision after about 6 weeks that can perist for months after returning to Earth. Balance is also impaired as inner ear receptors are affected, with returning astronauts often experiencing dizziness. More minor problems include puffiness of the face, flatulence, weight loss, nasal congestion, sleeplessness and space sickness as the body tries to adapt to being weightless.

The European Space Agency is currently running a study with 12 volunteers spending 21 days in bed with their heads tilted 6 degrees below the horizontal, causing their bodies to react in similar ways to being weightless. They will not be allowed to get up for any reason. They will be divided into 3 groups. The first will use resistive and vibrating exercise machines. Another group will use the exercise machines and eat nutritional supplements with the control group being given no counter measures. After 21 days they get 4 months to recover before the groups are switched and the process repeated two more times until all groups have tried each regime.

One other noted effect of living in microgravity is that astronauts can grow up to 3 percent taller during a mission, returning to their usual height on return to Earth. To study the impact of this change on the spine NASA has installed Ultrasound 2 on the ISS as part of the Spinal Ultrasound Investigation.

"This is the very first time that spinal ultrasound will be used to evaluate the changes in the spine," said Scott A. Dulchavsky, M.D., Ph.D., principal investigator for the station study. "Today there is a new ultrasound device on the station that allows more precise musculoskeletal imaging required for assessment of the complex anatomy and the spine," Dulchavsky said. "The crew will be able to perform these complex evaluations in the next year due to a newly developed Just-In-Time training guide for spinal ultrasound, combined with refinements in crew training and remote guidance procedures."

Six crew members will serve as test subjects. An astronaut will scan a fellow crew member at 30, 90, and 150 days into the flight. Researchers will watch from the ground via streaming video downlinks. The ultrasound will focus on the cervical and lumbar areas of the spine and surrounding tissues. The test subjects will also undergo pre- and post-flight ultrasound and MRI scans on Earth to provide baseline data.

It is hoped that both studies will help to develop exercises to improve crew health and rehabilitation techniques when astronauts return to Earth and also will help crews prepare for future long-duration missions.