Introduction to the Frontiers Research Topic: Optimization of Exercise Countermeasures for Human Space Flight - Lessons From Terrestrial Physiology and Operational Considerations

Abstract

Exercise in space has evolved from rudimental testing into the multi-modal countermeasure (CM) program used on the International Space Station (ISS). However, with the constraints of future exploration missions, replicating this program will be a significant challenge. Recent ISS data suggest that crew now experience only relatively moderate levels of microgravity (μG)-induced adaptation, although significant variation remains, with some crew displaying marked changes despite significant time/effort investment. This suggests that the efficacy of exercise CMs is yet to be optimized for all individuals. With the current suite of exercise devices operational for almost a decade, and with exploration approaching, it is timely to re-visit the terrestrial literature to identify new knowledge relevant to the management of μG adaptation. As such, the aim of the Frontiers Research Topic Optimization of Exercise Countermeasures for Human Space Flight - Lessons from Terrestrial Physiology and Operational Considerations, is to synthesize current terrestrial exercise physiology knowledge and consider how this might be employed to optimize the use of exercise CM. The purpose of this Perspective, which serves as a preface to the Research Topic is threefold: to briefly review the use and apparent efficacy of exercise in space, to consider the impact of the transition from ISS to exploration mission vehicles and habitats, and to identify areas of terrestrial exercise physiology where current knowledge might contribute to the optimization of CM exercise for exploration. These areas include individual variation, high intensity interval training, strength development/maintenance, concurrent training, plyometric/impact exercise, and strategies to enhance exercise efficacy.

Keywords: cardiovascular; exercise countermeasures; human space exploration; microgravity; musculoskeletal.

FIGURE 1

Hardware used for exercise countermeasures. Top Row (from left to right): ESA Astronaut Alexander Gerst exercising using the advanced resistive exercise device (ARED) on the International Space Station (ISS); Copyright: ESA/NASA: Id 312342); ESA Astronaut Frank de Winne using the T2 treadmill on ISS (Copyright: NASA: ISS021-E-007807); ESA Astronaut Luca Parmitano using the Cycle Ergometer with Vibration Isolation and Stabilization System (CEVIS) on ISS (Copyright: ESA/NASA: Id 300078). Middle Row (from left to right): NASA Astronaut Dan Tani, Expedition 16 Flight Engineer, using the Interim Resistive Exercise Device (iRED) on ISS (Copyright: NASA: ID iss016e027909); Astronaut Joseph Tanner, STS-97 Mission Specialist, using the cycle ergometer aboard the Space Shuttle Endeavour (Copyright: NASA: ID sts097-317-017); Astronaut Sandra Magnus, Expedition 18 Flight Engineer, equipped with a bungee harness, using the Treadmill with Vibration Isolation and Stabilization System (TVIS) in the Zvezda Service Module on ISS (Copyright: NASA: NASA ID iss018e030096). Bottom Row (from left to right): The ‘Apollo Exerciser’ used by Apollo 11 astronauts during their July 1969 mission (Photo by Eric F. Long, Smithsonian National Air and Space Museum [NASM 2009-4775] Used with Permission [Permission Number: 19-BK-063]); The Teflon-covered treadmill-like device used during Skylab 4 (Photo Credit: NASA).

FIGURE 2

Inter-individual variation in changes in bone mineral density (BMD) with long-duration spaceflight. Depicted are relative (%) changes from pre- to post-flight in ISS (n = 33, triangles) and Mir (n = 35, circles) crewmembers. BMD was measured using Dual-energy X-ray absorptiometry (DXA). (Figure reprinted with permission from: Evaluating Bone Loss in ISS Astronauts, Sibonga et al., 2015).