Presynaptic Modulation of Ia Afferents in Young and Old Adults When Performing Force and Position Control
Presynaptic Modulation of Ia Afferents in Young and Old Adults When Performing Force and Position Control
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DOI：
10.1152/jn.00839.2009
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发表时间：
2010-02-01
影响因子：
2.5
通讯作者：
Enoka, Roger M.
中科院分区：
文献类型：
--
作者：
Baudry, Stephane;Maerz, Adam H.;Enoka, Roger M.
Baudry S，Maerz AH，Enoka RM.年轻人和老年人进行力和位置控制时Ia传入神经的突触前调制。J Neurophysiol 103：623-631，2010.首次发表于2009年11月25日; doi：10.1152/jn.00839.2009。目前的工作调查突触前调制Ia传入桡侧腕伸肌（ECR）时，年轻人和老年人施加手腕伸展力，以支持惯性负载（位置控制）或实现一个等效的恒定扭矩对刚性约束（力控制）在5，10，和15%的最大力量。刺激手肘上桡神经诱发ECR内H反射。将条件刺激施加到手肘以上的正中神经以评估对同种异体Ia传入的突触前抑制（D1抑制），或施加到腕部（手掌分支）以评估对会聚到ECR运动神经元池的异种异体Ia传入的持续突触前抑制（异种异体Ia易化）。青年组在位置任务中D1抑制和异源Ia易化的发生率分别为79%和132.1%，而在力量任务中分别为69.1%和115.1%（P < 0.05）。相比之下，老年人在D1抑制（类似于72%）或异源性Ia易化（类似于114%）两项任务之间没有差异。收缩强度不影响D1抑制或异源性Ia促进的量为任何一组受试者。拮抗剂共激活的数量是相似的任务之间的年轻人，而它是更大的位置任务的老年人（P = 0.02）。这些数据表明，在年轻的成年人，老年人没有调制突触前抑制Ia传入控制时的位置，一个兼容的负载，而是增加了拮抗肌的共激活。
Baudry S, Maerz AH, Enoka RM. Presynaptic modulation of Ia afferents in young and old adults when performing force and position control. J Neurophysiol 103: 623-631, 2010. First published November 25, 2009; doi: 10.1152/jn.00839.2009. The present work investigated presynaptic modulation of Ia afferents in the extensor carpi radialis (ECR) when young and old adults exerted a wrist extension force either to support an inertial load (position control) or to achieve an equivalent constant torque against a rigid restraint (force control) at 5, 10, and 15% of the maximal force. H reflexes were evoked in the ECR by stimulating the radial nerve above the elbow. A conditioning stimulus was applied to the median nerve above the elbow to assess presynaptic inhibition of homonymous Ia afferents (D1 inhibition) or at the wrist (palmar branch) to assess the ongoing presynaptic inhibition of heteronymous Ia afferents that converge onto the ECR motor neuron pool (heteronymous Ia facilitation). The young adults had less D1 inhibition and greater heteronymous Ia facilitation during the position task (79 and 132.1%, respectively) compared with the force task (69.1 and 115.1%, respectively, P < 0.05). In contrast, the old adults exhibited no difference between the two tasks for either D1 inhibition (similar to 72%) or heteronymous Ia facilitation (similar to 114%). Contraction intensity did not influence the amount of D1 inhibition or heteronymous Ia facilitation for either group of subjects. The amount of antagonist coactivation was similar between tasks for young adults, whereas it was greater in the position task for old adults (P = 0.02). These data indicate that in contrast to young adults, old adults did not modulate presynaptic inhibition of Ia afferents when controlling the position of a compliant load but rather increased coactivation of the antagonist muscle.