AUTHOR=Bevelacqua Joseph J. , Welsh James , Mortazavi S. M. J. TITLE=Commentary: Introduction to the Frontiers Research Topic: Optimization of Exercise Countermeasures for Human Space Flight–Lessons From Terrestrial Physiology and Operational Considerations JOURNAL=Frontiers in Physiology VOLUME=10 YEAR=2019 URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.00915 DOI=10.3389/fphys.2019.00915 ISSN=1664-042X