Quadriceps muscle stimulation evokes heteronymous inhibition onto soleus with limited Ia activation compared to femoral nerve stimulation

• Type of Material: Article
• Authors: Mark Lyle, Emory University; Cristian Cuadra, Universidad Andres Bello; Steven L Wolf, Emory University
• Language: English
• Date: 2022-07-26
• Publisher: Springer Nature
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: Copyright © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature
• Final Published Version (URL): https://doi.org/10.1007%2Fs00221-022-06422-7
• Title of Journal or Parent Work: Experimental Brain Research
• Volume: 240
• Issue: 9
• Start Page: 2375
• End Page: 2388
• Grant/Funding Information: Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health under Award Number K01HD100588 and 1R01HD095975-01A1, as well as National Institute of Neurological Disorders and Stroke awards 5U01NS086607-05, U01NS166655, and 1U01NS102353-01.
• Keywords: Golgi tendon organ; Muscle spindle; Recurrent inhibition; Spinal reflex
• Research Categories: Biology, Neuroscience; Biology, Anatomy

Abstract

Heteronymous excitatory feedback from muscle spindles and inhibitory feedback from Golgi tendon organs and recurrent inhibitory circuits can influence motor coordination. The functional role of inhibitory feedback is difficult to determine because nerve stimulation, the primary method used in humans, cannot evoke inhibition without first activating the largest diameter muscle spindle axons. Here, we tested the hypothesis that quadriceps muscle stimulation could be used to examine heteronymous inhibition more selectively when compared to femoral nerve stimulation by comparing the effects of nerve and muscle stimulation onto ongoing soleus EMG held at 20% of maximal effort. Motor threshold and two higher femoral nerve and quadriceps stimulus intensities matched by twitch evoked torque magnitudes were examined. We found that significantly fewer participants exhibited excitation during quadriceps muscle stimulation when compared to nerve stimulation (14–29% vs 64–71% of participants across stimulation intensities) and the magnitude of heteronymous excitation from muscle stimulation, when present, was much reduced compared to nerve stimulation. Muscle and nerve stimulation resulted in heteronymous inhibition that significantly increased with increasing stimulation evoked torque magnitudes. This study provides novel evidence that muscle stimulation may be used to more selectively examine inhibitory heteronymous feedback between muscles in the human lower limb when compared to nerve stimulation.