Edgerton V R, Roy R R
Department of Physiological Science, University of California, Los Angeles, USA.
Adv Space Biol Med. 1994;4:33-67. doi: 10.1016/s1569-2574(08)60134-3.
The chronic "unloading" of the neuromuscular system during spaceflight has detrimental functional and morphological effects. Changes in the metabolic and mechanical properties of the musculature can be attributed largely to the loss of muscle protein and the alteration in the relative proportion of the proteins in skeletal muscle, particularly in the muscles that have an antigravity function under normal loading conditions. These adaptations could result in decrements in the performance of routine or specialized motor tasks, both of which may be critical for survival in an altered gravitational field, i.e., during spaceflight and during return to 1 G. For example, the loss in extensor muscle mass requires a higher percentage of recruitment of the motor pools for any specific motor task. Thus, a faster rate of fatigue will occur in the activated muscles. These consequences emphasize the importance of developing techniques for minimizing muscle loss during spaceflight, at least in preparation for the return to 1 G after spaceflight. New insights into the complexity and the interactive elements that contribute to the neuromuscular adaptations to space have been gained from studies of the role of exercise and/or growth factors as countermeasures of atrophy. The present chapter illustrates the inevitable interactive effects of neural and muscular systems in adapting to space. It also describes the considerable progress that has been made toward the goal of minimizing the functional impact of the stimuli that induce the neuromuscular adaptations to space.
太空飞行期间神经肌肉系统的长期“卸载”会产生有害的功能和形态学影响。肌肉组织代谢和力学特性的变化很大程度上可归因于肌肉蛋白的流失以及骨骼肌中蛋白质相对比例的改变，尤其是在正常负荷条件下具有抗重力功能的肌肉中。这些适应性变化可能导致日常或特殊运动任务的表现下降，而这两者对于在改变的重力场中生存（即在太空飞行期间以及返回1G重力环境期间）可能都至关重要。例如，伸肌质量的减少要求在执行任何特定运动任务时运动神经元池的募集比例更高。因此，被激活的肌肉会更快出现疲劳。这些后果凸显了开发技术以尽量减少太空飞行期间肌肉流失的重要性，至少是为太空飞行后返回1G重力环境做准备。通过研究运动和/或生长因子作为萎缩对策的作用，人们对神经肌肉适应太空的复杂性和相互作用因素有了新的认识。本章阐述了神经和肌肉系统在适应太空过程中不可避免的相互作用。它还描述了在实现将诱导神经肌肉适应太空的刺激的功能影响降至最低这一目标方面所取得的重大进展。
