Significant progress has been made in the development of countermeasures to attenuate the negative consequences of prolonged exposure to microgravity on astronauts’ bodies. Deconditioning of several organ systems during flight includes losses to cardiorespiratory fitness, muscle mass, bone density and strength. Similar deconditioning also occurs during prolonged bedrest; any protracted time immobile or inactive, especially for unwell older adults (e.g., confined to hospital beds), can lead to similar detrimental health consequences. Due to limitations in physiological research in space, the six-degree head-down tilt bedrest protocol was developed as ground-based analogue to spaceflight. A variety of exercise countermeasures have been tested as interventions to limit detrimental changes and physiological deconditioning of the musculoskeletal and cardiovascular systems. The Canadian Institutes of Health Research and the Canadian Space Agency recently provided funding for research focused on Understanding the Health Impact of Inactivity to study the efficacy of exercise countermeasures in a 14-day randomized clinical trial of six-degree head-down tilt bedrest study in older adults aged 55–65 years old (BROA). Here we will describe the development of a multi-modality countermeasure protocol for the BROA campaign that includes upper- and lower-body resistance exercise and head-down tilt cycle ergometry (high-intensity interval and continuous aerobic exercise training). We provide reasoning for the choice of these modalities following review of the latest available information on exercise as a countermeasure for inactivity and spaceflight-related deconditioning. In summary, this paper sets out to review up-to-date exercise countermeasure research from spaceflight and head-down bedrest studies, whilst providing support for the proposed research countermeasure protocols developed for the bedrest study in older adults.

/pdf/implementation-of-exercise-countermeasures-during-1a9v3ic1.pdf

Implementation of exercise countermeasures during spaceflight and microgravity analogue studies: Developing countermeasure protocols for bedrest in older adults (BROA)

Space colonization represents the most insidious challenge for mankind, as numerous obstacles affect the success of space missions. Specifically, the absence of gravitational forces leads to systemic physiological alterations, with particular emphasis on the musculoskeletal system. Indeed, astronauts exposed to spaceflight are known to report a significant impairment of bone microarchitecture and muscle mass, conditions clinically defined as osteoporosis and sarcopenia. In this context, space medicine assumes a crucial position, as the development of strategies to prevent and/or counteract weightlessness-induced alterations appears to be necessary. Furthermore, the opportunity to study the biological effects induced by weightlessness could provide valuable information regarding adaptations to spaceflight and suggest potential treatments that can preserve musculoskeletal health under microgravity conditions. Noteworthy, improving knowledge about the latest scientific findings in this field of research is crucial, as is thoroughly investigating the mechanisms underlying biological adaptations to microgravity and searching for innovative solutions to counter spaceflight-induced damage. Therefore, this narrative study review, performed using the MEDLINE and Google Scholar databases, aims to summarize the most recent evidence regarding the effects of real and simulated microgravity on the musculoskeletal system and to discuss the effectiveness of the main defence strategies used in both real and experimental settings.

/pdf/microgravity-and-musculoskeletal-health-what-strategies-pw8r83lo.pdf

Microgravity and Musculoskeletal Health: What Strategies Should Be Used for a Great Challenge?

Homo sapiens and their predecessors evolved in the context of the boundary conditions of Earth, including a 1 g gravity and a geomagnetic field (GMF). These variables, plus others, led to complex organisms that evolved under a defined set of conditions and define how humans will respond to space flight, a circumstance that could not have been anticipated by evolution. Over the past ~60 years, space flight and living in low Earth orbit (LEO) have revealed that astronauts are impacted to varying degrees by such new environments. In addition, it has been noted that astronauts are quite heterogeneous in their response patterns, indicating that such variation is either silent if one remained on Earth, or the heterogeneity unknowingly contributes to disease development during aging or in response to insults. With the planned mission to deep space, humans will now be exposed to further risks from radiation when traveling beyond the influence of the GMF, as well as other potential risks that are associated with the actual loss of the GMF on the astronauts, their microbiomes, and growing food sources. Experimental studies with model systems have revealed that hypogravity conditions can influence a variety biological and physiological systems, and thus the loss of the GMF may have unanticipated consequences to astronauts’ systems, such as those that are electrical in nature (i.e., the cardiovascular system and central neural systems). As astronauts have been shown to be heterogeneous in their responses to LEO, they may require personalized countermeasures, while others may not be good candidates for deep-space missions if effective countermeasures cannot be developed for long-duration missions. This review will discuss several of the physiological and neural systems that are affected and how the emerging variables may influence astronaut health and functioning.

/pdf/homo-sapiens-a-species-not-designed-for-space-flight-health-179v4bct.pdf

Homo sapiens—A Species Not Designed for Space Flight: Health Risks in Low Earth Orbit and Beyond, Including Potential Risks When Traveling beyond the Geomagnetic Field of Earth

Responses of neuromuscular properties to unloading and potential countermeasures during space exploration missions

Intrinsic circadian clocks generate circadian rhythms of physiology and behavior, which provide the capabilities to adapt to cycling environmental cues that result from the self-rotation of the Earth. Circadian misalignment leads to deleterious impacts on adaptation and health in different organisms. The environmental cues on the interplanetary journey to and on Mars dramatically differ from those on Earth. These differences impose numerous adaptive challenges, including challenges for humans’ circadian clock. Thus, adaptation of circadian rhythms to the Martian environment is a prerequisite for future landing and dwelling on Mars. Here, we review the progress of studies associated with the influence of the Martian environment on circadian rhythms and propose directions for further study and potential strategies to improve the adaptation of the circadian clock for future Mars missions.

/pdf/how-to-live-on-mars-with-a-proper-circadian-clock-2r6und3g.pdf

How to Live on Mars With a Proper Circadian Clock?

The purpose of this systematic review is twofold: 1) to identify, evaluate, and synthesize the heretofore disparate scientific literatures regarding the effects of direct exposure to microgravity on the musculoskeletal system, taking into account for the first time both bone and muscle systems of both humans and animals; and 2) to investigate the efficacy and limitations of exercise countermeasures on the musculoskeletal system under microgravity in humans.The Framework for Scoping Studies (Arksey and O'Malley 2005) and the Cochrane Handbook for Systematic Reviews of Interventions (Higgins JPT 2011) were used to guide this review. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist was utilized in obtaining the combined results (Moher, Liberati et al. 2009). Data sources, PubMed, Embase, Scopus, and Web of Science were searched for published articles through October 2019 using the Mesh terms of microgravity, musculoskeletal system, and exercise countermeasures. A total of 84 references were selected, including 40 animal studies and 44 studies with human participants. The heterogeneity in the study designs, methodologies, and outcomes deemed this review unsuitable for a meta-analysis. Thus, we present a narrative synthesis of the results for the key domains under five categories: 1) Skeletal muscle responses to microgravity in humans 2) Skeletal muscle responses to microgravity in animals 3) Adaptation of the skeletal system to microgravity in humans 4) Adaptation of the skeletal system to microgravity in animals 5) Effectiveness of exercise countermeasures on the human musculoskeletal system in microgravity. Existing studies have produced only limited data on the combined effects on bone and muscle of human spaceflight, despite the likelihood that the effects on these two systems are complicated due to the components of the musculoskeletal system being anatomically and functionally interconnected. Bone is directly affected by muscle atrophy as well as by changes in muscle strength, notably at muscle attachments. Given this interplay, the most effective exercise countermeasure is likely to be robust, individualized, resistive exercise, primarily targeting muscle mass and strength.

/pdf/the-effects-of-spaceflight-microgravity-on-the-yhz0p5uncx.pdf

The effects of spaceflight microgravity on the musculoskeletal system of humans and animals, with an emphasis on exercise as a countermeasure: a systematic scoping review.

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The effects of spaceflight microgravity on the musculoskeletal system of humans and animals, with an emphasis on exercise as a countermeasure: a systematic scoping review.