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7. The model demonstrates that when the knees are locked the joints of the ankles and hips become coupled together so that movement of one is accompanied by movement of the others. The strength of this coupling increases with stance width. The stiffness of the legs-pelvic structure is therefore passively increased by increasing stance width. 

8. Coupling of the hips and ankles also predicts an increase in proprioceptive sensitivity to lateral motion about the ankles with increasing stance width, a factor which may contribute to the observed reduction in lateral motion. At the same time the model predicts that information from receptors in the head (visual and vestibular) become less sensitive in the detection of lateral motion about the ankles with increasing stance width. This may explain why vision was less effective in reducing lateral velocity of the body with greater stance widths.

 INTRODUCTION

 Even when attempting to stand still the upright human body continues to move. For a healthy person these residual movements are usually not a problem since the magnitude of body motion that remains is too small to threaten equilibrium; the vertical projection of the body's centre of mass can be readily maintained within the area of support bounded by the outer edges of the feet. However, difficulty may be experienced by patients with central nervous system damage when attempting to stand upright because of excessive sway. The pattern of residual body motion may be quite different for patients with lesions at different sites. For example, patients with alcoholic cerebellar degeneration predominantly affecting the anterior lobe of the cerebellum have been reported to exhibit pronounced anteroposterior body movements at around 3 Hz when standing with eyes closed (Mauritz, Dichgans & Hufschmidt, 1979) whereas patients with Friedreich's ataxia affecting posterior columns and spinocerebellar input exhibit lower frequency (<1 Hz) body movements which tend to have a stronger lateral sway component (Diener, Dichgans, Bacher & Gompf, 1984). Lesions of the vestibulocerebellar connections result in multi- directional low-frequency body oscillations (Diener et al. 1984) while patients with lesions of the cerebellar hemispheres have been found to be either indistinguishable from healthy subjects (Diener et al. 1984) or to show enhanced sway with a directional preponderance to the left and right (Umemura, Ishizaki, Matsuoka, Hoshino & Nozue, 1989). In some unilateral thalamic lesions (Masdeu & Gorelick, 1988) and unilateral basal ganglia lesions (Labadie, Awerbuch, Hamilton & Rapcsak, 1989) pronounced dysequilibrium can occur such that the patient often falls in a direction away from the side of the lesion. Patients with Wallenberg's syndrome following a lateral medullary infarct exhibit a diagonal pattern of body sway, from right forward to left backward for right sided lesions and from left forward to right backward for left sided lesions (Dieterieh & Brandt, 1992). In an effort to understand such direction-specific postural deficits we have analysed some of the mechanical and neural factors that influence normal, residual body motion in three dimensions during quiet stance. 

When considering direction-specific instability it may be important to make allowance for mechanical differences in the skeletal structure between the sagittal and frontal planes. Structural differences in these two principal planes are

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 7. 该模型表明，当膝盖锁定时，脚踝和臀部的关节会连接在一起，因此一个的运动伴随着另一个的运动。 这种耦合的强度随着站立宽度的增加而增加。 因此，通过增加站姿宽度被动地增加腿部-骨盆结构的刚度。

 8. 髋关节和踝关节的结合也预示着随着站立宽度的增加，对围绕踝关节横向运动的本体感觉敏感性增加，这一因素可能有助于观察到的横向运动减少。 同时，该模型预测来自头部受体（视觉和前庭）的信息在检测踝关节横向运动时会随着站立宽度的增加而变得不那么敏感。 这可以解释为什么视觉在降低站立宽度较大的身体横向速度方面效果较差。

  介绍

  即使试图站立不动，直立的人体也会继续移动。 对于健康人来说，这些残余运动通常不是问题，因为剩余的身体运动幅度太小，不足以威胁到平衡； 身体重心的垂直投影可以很容易地保持在由脚的外边缘限定的支撑区域内。 然而，中枢神经系统受损的患者在尝试直立时可能会因为过度摇摆而遇到困难。 对于不同部位病变的患者，残余身体运动的模式可能大不相同。 例如，据报道，主要影响小脑前叶的酒精性小脑变性患者在闭眼站立时表现出约 3 Hz 的明显前后身体运动 (Mauritz, Dichgans & Hufschmidt, 1979)，而患有弗里德赖希共济失调的患者则影响小脑前叶。 柱和脊髓小脑输入表现出较低频率 (<1 Hz) 的身体运动，这些身体运动往往具有更强的横向摇摆分量 (Diener, Dichgans, Bacher & Gompf, 1984)。 前庭小脑连接的损伤导致多向低频身体振荡（Diener et al. 1984），而小脑半球损伤的患者被发现与健康受试者无法区分（Diener et al. 1984）或显示 以向左和向右的方向优势增强摇摆（Umemura、Ishizaki、Matsuoka、Hoshino 和 Nozue，1989）。 在一些单侧丘脑病变 (Masdeu & Gorelick, 1988) 和单侧基底节病变 (Labadie, Awerbuch, Hamilton & Rapcsak, 1989) 中，可能会出现明显的平衡失调，使得患者经常向远离病变一侧的方向跌倒。 外侧延髓梗死后的 Wallenberg 综合征患者表现出身体倾斜的倾斜模式，右侧病变从右向前向左向后，左侧病变从左向前向右后 (Dieterieh & Brandt, 1992)。 为了理解这种特定方向的姿势缺陷，我们分析了一些机械和神经因素，这些因素影响安静站立期间三个维度的正常残余身体运动。

 在考虑特定方向的不稳定性时，考虑矢状面和额状面之间骨骼结构的机械差异可能很重要。 这两个主平面的结构差异是

Dì 480 yè.

7. Gāi móxíng biǎomíng, dāng xīgài suǒdìng shí, jiǎohuái hé túnbù de guānjié huì liánjiē zài yīqǐ, yīncǐ yīgè de yùndòng bànsuízhe lìng yīgè de yùndòng. Zhè zhǒng ǒuhé de qiángdù suízhe zhànlì kuāndù de zēngjiā ér zēngjiā. Yīncǐ, tōngguò zēngjiā zhàn zī kuāndù bèidòng dì zēngjiā tuǐ bù-gǔpén jiégòu de gāngdù.

8. Kuān guānjiéhé huái guānjié de jié hé yě yùshìzhe suízhe zhànlì kuāndù de zēngjiā, duì wéirào huái guānjié héngxiàng yùndòng de běntǐ gǎnjué mǐngǎn xìng zēngjiā, zhè yī yīnsù kěnéng yǒu zhù yú guānchá dào de héngxiàng yùndòng jiǎnshǎo. Tóngshí, gāi móxíng yùcè láizì tóu bù shòu tǐ (shìjué hé qiántíng) de xìnxī zài jiǎncè huái guānjié héngxiàng yùndòng shí huì suízhe zhànlì kuāndù de zēngjiā ér biàn dé bù nàme mǐngǎn. Zhè kěyǐ jiěshì wèishéme shìjué zài jiàngdī zhànlì kuāndù jiào dà de shēntǐ héngxiàng sùdù fāngmiàn xiàoguǒ jiào chà.

 Jièshào

 jíshǐ shìtú zhànlì bù dòng, zhílì de réntǐ yě huì jìxù yídòng. Duìyú jiànkāng rén lái shuō, zhèxiē cányú yùndòng tōngcháng bùshì wèntí, yīnwèi shèngyú de shēntǐ yùndòng fúdù tài xiǎo, bùzú yǐ wēixié dào pínghéng; shēntǐ zhòngxīn de chuízhí tóuyǐng kěyǐ hěn róngyì dì bǎochí zài yóu jiǎo de wài bian yuán xiàndìng de zhīchēng qūyù nèi. Rán'ér, zhōngshū shénjīng xìtǒng shòu sǔn de huànzhě zài chángshì zhílì shí kěnéng huì yīn wéi guòdù yáobǎi ér yù dào kùnnán. Duìyú bùtóng bùwèi bìngbiàn de huànzhě, cányú shēntǐ yùndòng de móshì kěnéng dà bù xiāngtóng. Lìrú, jù bàodào, zhǔyào yǐngxiǎng xiǎonǎo qián yè de jiǔjīng xìng xiǎonǎo biànxìng huànzhě zài bì yǎn zhànlì shí biǎoxiàn chū yuē 3 Hz de míngxiǎn qiánhòu shēntǐ yùndòng (Mauritz, Dichgans& Hufschmidt, 1979), ér huàn yǒu fú lǐ dé lài xī gòng jì shītiáo de huànzhě zé yǐngxiǎng xiǎonǎo qián yè. Zhù hé jǐsuǐ xiǎonǎo shūrù biǎoxiàn chū jiào dīpínlǜ (<1 Hz) de shēntǐ yùndòng, zhèxiē shēntǐ yùndòng wǎngwǎng jùyǒu gèng qiáng de héngxiàng yáobǎi fènliàng (Diener, Dichgans, Bacher& Gompf, 1984). Qiántíng xiǎonǎo liánjiē de sǔnshāng dǎozhì duō xiàng dī pín shēntǐ zhèndàng (Diener et al. 1984), Ér xiǎonǎo bànqiú sǔnshāng de huànzhě pī fà xiàn yǔ jiànkāng shòu shì zhě wúfǎ qūfēn (Diener et al. 1984) Huò xiǎnshì yǐ xiàng zuǒ hé xiàng yòu de fāngxiàng yōushì zēngqiáng yáobǎi (Umemura,Ishizaki,Matsuoka,Hoshino hé Nozue,1989). Zài yīxiē dān cè qiūnǎo bìngbiàn (Masdeu& Gorelick, 1988) hé dān cè jīdǐ jié bìngbiàn (Labadie, Awerbuch, Hamilton& Rapcsak, 1989) zhōng, kěnéng huì chūxiàn míngxiǎn de pínghéng shītiáo, shǐdé huànzhě jīngcháng xiàng yuǎnlí bìngbiàn yī cè de fāngxiàng diédǎo. Wàicè yánsuǐ gěngsǐ hòu de Wallenberg zònghé zhēng huànzhě biǎoxiàn chū shēntǐ qīngxié de qīngxié móshì, yòu cè bìngbiàn cóng yòu xiàng qián xiàng zuǒ xiàng hòu, zuǒ cè bìngbiàn cóng zuǒ xiàng qián xiàng yòu hòu (Dieterieh& Brandt, 1992). Wèile lǐjiě zhè zhǒng tèdìng fāngxiàng de zīshì quēxiàn, wǒmen fēnxīle yīxiē jīxiè hé shénjīng yīnsù, zhèxiē yīnsù yǐngxiǎng ānjìng zhànlì qíjiān sān gè wéidù de zhèngcháng cányú shēntǐ yùndòng.

Zài kǎolǜ tèdìng fāngxiàng de bù wěndìng xìng shí, kǎolǜ shǐ zhuàng miàn hé é zhuàng miàn zhī jiān gǔgé jiégòu de jīxiè chāyì kěnéng hěn zhòngyào. Zhè liǎng gè zhǔ píngmiàn de jiégòu chāyì shì