Define Changes in Body Composition due to Microgravity?

Major stress in space is microgravity. Microgravity refers to an environment in which there is very little net gravitational force, as of a free-falling object, an orbit, or interstellar space. Now let us look at the effects of microgravity, which are listed in Table 18.10.

Several of the patho physiological changes associated with space flight manifest .themselves as the changes in body composition. Space flight presents a unique  challenge for quantifying body composition changes since fluid, bone, muscle and  adipose tissue levels all vary independently of one another in space, and body weight  loss does not follow classical pattern. The body mass measurements were taken for the first time during 28 to 84 day Skylab mission and revealed 0.91 to 3.64 kg losses of pre flight body weight; Analysis of component of the weight loss was based on both direct whole body measurements and on indirect metabolic balance data. A conclusion from the analysis was that more than half of the weight loss was from fat free mass remaining from the fat stores. About half of the total weight loss that occurred within the first two days of flight was due to water loss. All studies of fluid balance during microgravity have indicated a decrease in total body fluids of approximately 500-900 ml.

Most important is muscle loss and limited resistive exercise by crewmembers have been helpful in prevention upto some extent. Skeletal losses unlike muscle losses do appear to be related to the length of flight. About 0.4% to 1.0% of bone minerals are lost per month during space-flight. The role of nutrition in musculoskeletal losses during space flight has not been clearly defined, but data from Skylab mission demonstrate negative nitrogen and potassium balance despite supposedly adequate ingestion of energy and protein. Return to earth poses a major concern. Stress fractures, muscle pulls, ligament stress and inability to ambulate occur and may take 2-8 weeks to resolve. Although experience with long-term space flight has provided considerable confidence in the ability of human body to recover from space flight and readapt to the earth environment, effects observed on the long Sky lab, Mir and Shuttle-Mir missions have convinced the researchers that countermeasures and monitoring are essential to success of space flight.