Primary (Ia) sensory afferents that innervate muscle spindles provide strong synaptic input to homonymous motoneurons and are thought to play a role in balance control. In addition, Ia afferents have broad heteronymous connections; i.e., projections to motoneurons that innervate other muscles that act at the same joint as well as at different joints. The purpose of the current study was to investigate heteronymous Ia afferent connections from the triceps surae muscles to lower limb and back muscles during quiet standing in humans. We applied supra-threshold noisy vibration (10−115 Hz) to the right Achilles tendon of 12 participants maintaining quiet stance and recorded EMG activity bilaterally from homonymous (Soleus) and heteronymous muscles (Semitendinosus, Vastus Lateralis, Erector Spinae). We estimated coherence, phase, and gain between the tendon probe acceleration and rectified EMG from each muscle. We found significant coherence between the probe acceleration and EMG in ipsilateral Soleus (5−100 Hz), Semitendinosus (10−75 Hz), Vastus Lateralis (5-70 Hz), and bilateral Erector Spinae muscles (10−70 Hz). These results provide evidence that triceps surae muscle spindle afferents can influence the activity of muscles proximal to the ankle joint across a broad frequency band during quiet standing.

支配肌肉纺锤体的初级（Ia）感觉传入神经为同音运动神经元提供强大的突触输入，并被认为在平衡控制中发挥作用。另外，Ia传入具有广泛的异质连接；即，运动神经元的投影会支配作用于同一关节以及不同关节的其他肌肉。本研究的目的是调查人静静站立时从肱三头肌到下肢和背部肌肉的异种Ia传入连接。我们对12名保持安静姿势的参与者的右跟腱施加超阈值噪声振动（10−115 Hz），并记录了同音肌（Soleus）和异肌（Semitendinosus，Vastus Lateralis，Erector Spinae）的EMG活动。我们估算了相干性，相位，并在每根肌肉的肌腱探针加速度和矫正肌电图之间获得增益。我们发现在同侧比目鱼肌（5-100 Hz），半腱肌（10-75 Hz），侧头肌（5-70 Hz）和双侧竖脊肌（10-70 Hz）中，探头加速度与EMG之间具有显着的一致性。这些结果提供了证据，表明在安静站立期间，肱三头肌肱三头肌肌梭传入神经可在宽频带上影响踝关节近端的肌肉活动。