scientific flight investigations prevents consensus on specific protocols for maintaining fitness. The Strategy report emphasizes that the paucity of flight experiment opportunities necessitates greater reliance on ground-based models for refining hypotheses and assessing countermeasure efficacy and implementation. In the era of ISS, progress on preventing muscle debilitation will depend greatly on the close coordination of medical operations monitoring of crew health and fitness with basic research flight investigations on humans. New technologies for noninvasive monitoring of muscle health during spaceflight are being developed. This should achieve the Strategy report goal of improved documentation of individual astronaut’s history of muscle use to control for intersubject variation and reduce uncontrolled variables. In the past, countermeasure testing and validation were not the primary objectives of spaceflight missions. Without manifesting them as high-priority goals, as recommended in the Strategy report, and instituting a formal process to incorporate potential countermeasures from both intra- and extramural laboratories, progress in solving muscle-related problems will fall further behind that required to support the continuous presence of humans in space. Congruent with the Strategy report, the muscle research program is putting great effort into understanding the basic cellular and molecular mechanisms for atrophy, weakness, and susceptibility to injury. Progress is being to be made in defining how muscle cells sense working length and load imposed by gravity through unloading and hypergravity ground-based studies of normal and genetically altered rodents, as recommended by the Strategy report. These studies are exploring hormones, growth factors, second messengers, and drugs that potentially translate into novel countermeasure applications. Additional studies called out in the Strategy report are needed to examine nerve and muscle repair, failed microcirculation, and fundamental aspects of myogenesis and regeneration because muscle damage and repair during spaceflight are inevitable in spite of rigorous safety practices and countermeasures.


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