Abstract：
Prolonged bed rest impairs standing balance but the underlying mechanisms are uncertain. Previous research suggests strength loss is not the cause, leaving impaired sensorimotor control as an alternative. Here we examine vestibular control of posture in 18 male volunteers before and after 60 days of bed rest. Stochastic vestibular stimulation (SVS) was used to evoke sway responses before, 1 and 6 days after bed rest under different head yaw orientations. The directional accuracy and precision of these responses were calculated from ground reaction force vectors. Bed rest caused up to 63% increases in spontaneous standing sway and 31% reductions in leg strength, changes which were uncorrelated. The increase in sway was exacerbated when the eyes were closed. Mean directions of SVS-evoked sway responses were unaffected, being directed towards the anodal ear and rotating in line with head orientation in the same way before and after bed rest. However, individual trial analysis revealed 25%-30% increases in directional variability, which were significantly correlated with the increase in spontaneous sway (r = 0.48-0.71; P ≤ 0.044) and were still elevated on day 6 post-bed rest. This reveals that individual sway responses may be inappropriately oriented, a finding masked by the averaging process. Our results confirm that impaired balance following prolonged bedrest is not related to loss of strength. Rather, they demonstrate that the sensorimotor transformation process which converts vestibular feedback into appropriately directed balance responses is impaired. KEY POINTS: Prolonged inactivity impairs balance but previous research suggests this is not caused by loss of strength. Here we investigated vestibular control of balance before and after 60 days of bed rest using electrical vestibular stimulation (EVS) to evoke sway responses. Spontaneous sway significantly increased and muscle strength reduced following bed rest, but, in keeping with previous research, these two effects were not correlated. While the overall accuracy of EVS-evoked sway responses was unaffected, their directional variability significantly increased following bed rest, and this was correlated with the increases in spontaneous sway. We have shown that the ability to transform head-centred vestibular feedback into an appropriately directed body sway response is negatively affected by prolonged inactivity; this may contribute to the impaired balance commonly observed following bed rest.
摘要：
长时间的卧床休息会损害站立平衡，但潜在的机制尚不确定。以前的研究表明，力量损失不是原因，留下受损的感觉运动控制作为替代。在这里，我们检查了18名男性志愿者在卧床休息60天之前和之后的前庭姿势控制。之前使用随机前庭刺激(SVS)来唤起摇摆反应，床后1天和6天，在不同的头部偏航取向下休息。这些响应的方向精度和精度是从地面反作用力矢量计算的。卧床休息导致自发性站立摇摆增加63％，腿部力量减少31％，不相关的变化。当眼睛闭合时,摇摆的增加加剧。SVS诱发摇摆反应的平均方向不受影响，指向阳极耳，并在卧床前后以相同的方式与头部方向一致旋转。然而,个别试验分析显示方向变异性增加25%-30%，与自发摇摆的增加显着相关（r=0.48-0.71；P≤0.044），并且在卧床休息后第6天仍然升高。这表明，个人摇摆反应可能是不恰当的，被平均过程掩盖的发现。我们的结果证实，长时间卧床休息后平衡受损与力量丧失无关。相反，他们证明，将前庭反馈转化为适当定向的平衡反应的感觉运动转化过程受损。关键点：长时间不活动会损害平衡，但先前的研究表明这不是由力量损失引起的。在这里，我们使用电前庭刺激（EVS）引起摇摆反应，研究了卧床休息60天之前和之后的前庭平衡控制。卧床休息后，自发性摇摆显着增加，肌肉力量降低，但是,与之前的研究一致,这两种效应并不相关。虽然EVS诱发摇摆反应的整体准确性不受影响，他们的方向变异性在卧床休息后显著增加，这与自发摇摆的增加有关。我们已经证明，长时间不活动会对将以头部为中心的前庭反馈转化为适当定向的身体摇摆反应的能力产生负面影响；这可能导致卧床休息后通常观察到的平衡受损。
