Exercise Neuroscience Research Group, University of São Paulo, Brazil.
School of Arts, Sciences and Humanities, University of São Paulo, Brazil.
J Gerontol A Biol Sci Med Sci. 2021 Mar 31;76(4):568-575. doi: 10.1093/gerona/glab010.
Age-related changes in presynaptic inhibition (PSI) have not been observed during gait initiation, which requires anticipatory postural adjustment (APA). As APA is centrally modulated and is impaired in older compared to young adults, here we aimed to study the presynaptic control and co-contraction levels in the ankle muscles during gait initiation in older compared to young adults. Fifteen older (age range 65-80 years) and 15 young adults (age range 19-30 years) performed a gait initiation task on a force platform under 3 conditions: (i) without electrical stimulation; (ii) test Hoffman reflex (H-reflex); and (iii) conditioned H-reflex. H-reflexes were evoked on the soleus muscle when the APA amplitude exceeded 10%-20% of the average baseline mediolateral force. Participants also performed quiet stance as a control task. Results showed that both age groups presented similar PSI levels during quiet stance (p = .941), while in the gait initiation older adults presented higher PSI levels, longer duration, and lower amplitude of APA than young adults (p < .05). Older adults presented higher co-contraction ratio in both tasks than young adults (p < .05). Correlations between the PSI levels and the APA amplitude (r = -0.61, p = .008), and between the PSI levels and the co-contraction ratio during gait initiation (r = -0.64, p = .005) were found for older adults only. APA amplitude explained 49% of the variance of the PSI levels (p = .003). Our findings suggest that older compared to young adults have increased presynaptic control to compensate for the decreased supraspinal modulation on impaired APAs during gait initiation.
年龄相关的突触前抑制（PSI）变化在步态启动过程中尚未观察到，而步态启动需要预期姿势调整（APA）。由于 APA 是中枢调节的，并且在老年人中比年轻人更受损，因此我们旨在研究老年人和年轻人在步态启动过程中踝关节肌肉的突触前控制和共同收缩水平。15 名老年人（年龄范围 65-80 岁）和 15 名年轻人（年龄范围 19-30 岁）在力平台上完成了步态启动任务，共 3 种情况：（i）无电刺激；（ii）测试霍夫曼反射（H 反射）；（iii）条件性 H 反射。当 APA 幅度超过平均基线横向力的 10%-20%时，在比目鱼肌上诱发 H 反射。参与者还进行了安静站立作为对照任务。结果表明，两个年龄组在安静站立时都表现出相似的 PSI 水平（p=.941），而在步态启动时，老年人的 APA 幅度更高、持续时间更长、PSi 水平更高比年轻人（p <.05）。老年人在两项任务中的共同收缩比年轻人更高（p <.05）。老年人仅在步态启动时的 PSI 水平与 APA 幅度（r = -0.61，p =.008）和 PSI 水平与共同收缩比之间存在相关性（r = -0.64，p =.005）。仅老年人的 APA 幅度解释了 PSI 水平变化的 49%（p =.003）。我们的研究结果表明，与年轻人相比，老年人的突触前控制增加，以补偿步态启动时 APA 受损导致的上运动神经元调节减弱。
