ABSTRACT
Rodent muscles have been examined in more than 89 spaceflight studies over the last 25 years with much variation in the procedures and results. Mission duration ranged from four days to three weeks, postflight data collection ranged from a few hours to two days after landing, and there is great diversity in the number, size, and age of the rats that have flown. Several different types and sizes of animal enclosures have also been used--a significant factor because cage design affects animal activity and muscle loading. Only a small percentage (approximately 16%) of the total number of striated muscles in the rat have been examined. We have identified both substantial redundancy and inconsistencies in the results from studies to date. However, many of these appear unavoidable due to the great variation in experimental protocol of the different missions. Nevertheless these studies repeatedly confirm that exposure to spaceflight decreases the mass of limb muscles and leads to muscle atrophy. The majority of missions were flown by the former Soviet Union, but the majority of papers have been published by U.S. researchers. A relatively small number of investigators (about 50) clustered into fewer than 15 identifiable research groups worldwide account for most of the results to date. These groups have had access to rodent muscle tissue from two to seven spaceflights each. International cooperation in the post-cold war era and the publication of future work in peer-reviewed international journals should help greatly in reducing redundancy and enriching our knowledge of how gravity affects biological systems.