Steele James, Androulakis-Korakakis Patroklos, Perrin Craig, Fisher James Peter, Gentil Paulo, Scott Christopher, Rosenberger André
School of Sport, Health, and Social Sciences, Solent University, Southampton, United Kingdom.
Ukactive Research Institute, London, United Kingdom.
Front Physiol. 2019 Sep 10;10:1150. doi: 10.3389/fphys.2019.01150. eCollection 2019.
Prolonged periods in microgravity (μG) environments result in deconditioning of numerous physiological systems, particularly muscle at molecular, single fiber, and whole muscle levels. This deconditioning leads to loss of strength and cardiorespiratory fitness. Loading muscle produces mechanical tension with resultant mechanotransduction initiating molecular signaling that stimulates adaptations in muscle. Exercise can reverse deconditioning resultant from phases of detraining, de-loading, or immobilization. On Earth, applications of loading using exercise models are common, as well as in μG settings as countermeasures to deconditioning. The primary modalities include, but are not limited to, aerobic training (or "cardio") and resistance training, and have historically been dichotomized; the former primarily thought to improve cardiorespiratory fitness, and the latter primarily improving strength and muscle size. However, recent work questions this dichotomy, suggesting adaptations to loading through exercise are affected by intensity of effort independent of modality. Furthermore, similar adaptations may occur where sufficient intensity of effort is used. Traditional countermeasures for μG-induced deconditioning have focused upon engineering-based solutions to enable application of traditional models of exercise. Yet, contemporary developments in understanding of the applications, and subsequent adaptations, to exercise induced muscular loading in terrestrial settings have advanced such in recent years that it may be appropriate to revisit the evidence to inform how exercise can used in μG. With the planned decommissioning of the International Space Station as early as 2024 and future goals of manned moon and Mars missions, efficiency of resources must be prioritized. Engineering-based solutions to apply exercise modalities inevitably present issues relating to devices mass, size, energy use, heat production, and ultimately cost. It is necessary to identify exercise countermeasures to combat deconditioning while limiting these issues. As such, this brief narrative review considers recent developments in our understanding of skeletal muscle adaptation to loading through exercise from studies conducted in terrestrial settings, and their applications in μG environments. We consider the role of intensity of effort, comparisons of exercise modalities, the need for concurrent exercise approaches, and other issues often not considered in terrestrial exercise studies but are of concern in μG environments (i.e., O consumption, CO production, and energy costs of exercise).
长时间处于微重力（μG）环境会导致许多生理系统功能失调，尤其是在分子、单纤维和全肌肉水平上的肌肉。这种功能失调会导致力量和心肺功能下降。对肌肉施加负荷会产生机械张力，由此引发的机械转导会启动分子信号传导，从而刺激肌肉适应。运动可以逆转因停训、卸载或固定阶段导致的功能失调。在地球上，使用运动模型进行负荷训练很常见，在μG环境中也是对抗功能失调的对策。主要方式包括但不限于有氧训练（或“有氧运动”）和阻力训练，并且历来被分为两类；前者主要被认为可改善心肺功能，后者主要改善力量和肌肉大小。然而，最近的研究对这种二分法提出了质疑，表明通过运动对负荷的适应受努力强度的影响，而与运动方式无关。此外，在使用足够努力强度的情况下可能会出现类似的适应情况。针对μG引起的功能失调的传统对策主要集中在基于工程的解决方案上，以实现传统运动模型的应用。然而，近年来，在理解陆地环境中运动诱导的肌肉负荷的应用及后续适应方面的当代发展取得了很大进展，以至于可能有必要重新审视相关证据，以了解如何在μG环境中使用运动。随着国际空间站最早将于2024年退役以及载人月球和火星任务的未来目标，必须优先考虑资源效率。基于工程的应用运动方式的解决方案不可避免地会出现与设备质量、尺寸、能源使用、热量产生以及最终成本相关的问题。有必要确定运动对策以对抗功能失调，同时限制这些问题。因此，本简要叙述性综述考虑了我们从陆地环境研究中对骨骼肌通过运动适应负荷的理解的最新进展，以及它们在μG环境中的应用。我们考虑了努力强度的作用、运动方式的比较、同时进行运动方法的必要性，以及其他在陆地运动研究中通常不考虑但在μG环境中令人关注的问题（即运动的氧气消耗、二氧化碳产生和能量成本）。
