Heteronymous muscle responses to noisy achilles tendon vibration during standing


Background and Aim: Primary (Ia) afferents have been shown to influence both homonymous (parent muscle) and heteronymous (muscles other than the parent muscle) motoneurons. Specifically, the Ia muscle spindle afferents of Soleus have been shown to influence motoneurons of muscles acting at the knee and hip joints through both monosynaptic and polysynaptic pathways in humans [1,2]. The purpose of this study was to investigate the heteronymous (thigh and back muscle) responses to noisy Achilles tendon vibration during quiet standing. Methods: Noisy vibration (10-115 Hz) was applied to right Achilles tendon to investigate the frequency characteristics of the heteronymous responses in bilateral Semitendinosus, Vastus Lateralis, and Erector Spinae muscles. Participants (n=12; 5 Male) maintained standing balance for a series of two minute trials. Coherence was estimated between the tendon probe acceleration (input signal) and the rectified EMG (output signal) of each muscle. Results: We found significant coherence between the tendon probe acceleration and the EMG of ipsilateral Soleus (across a 10-70 Hz bandwidth), Semitendinosus (10-60 Hz), and Vastus Lateralis (10-60 Hz). Responses were observed bilaterally in Erector Spinae (10-50 Hz), with both ipsilateral and contralateral muscles showing similar coherence. Conclusions: Results from this study provide evidence that muscle spindle feedback from the triceps surae influences the activity of proximal muscles that are important for the control of standing balance. [1] Pierrot-Deseilligny et al., Exp. Brain Res. 42, 337-350, 1981; [2] Meunier et al., Exp. Brain Res. 96, 534-544, 1993;

Acknowledgments: Funded by NSERC