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Reduced inhibition from quadriceps onto soleus after acute quadriceps fatigue suggests Golgi tendon organ contribution to heteronymous inhibition
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  • Cristian Cuadra,
  • Adam DeBoef,
  • Sarah Luong,
  • SL Wolf,
  • Richard Nichols,
  • Mark Lyle
Cristian Cuadra
University at Buffalo
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Adam DeBoef
Georgia Institute of Technology
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Sarah Luong
Emory University School of Medicine
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SL Wolf
Emory University School of Medicine
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Richard Nichols
Georgia Institute of Technology
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Mark Lyle
Emory University School of Medicine

Corresponding Author:[email protected]

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Abstract

Heteronymous inhibition between lower limb muscles is primarily attributed to recurrent inhibitory circuits in humans but could also arise from Golgi tendon organs (GTOs). Distinguishing between recurrent inhibition and mechanical activation of GTOs is challenging because their heteronymous effects are both elicited by stimulation of nerves or a muscle belly above motor threshold. Here, the unique influence of mechanically activated GTOs was examined by comparing the magnitude of heteronymous inhibition from quadriceps (Q) muscle belly stimulation onto ongoing soleus (SOL) EMG at five Q stimulation intensities (1.5-2.5x motor threshold) before and after an acute bout of stimulation-induced Q fatigue. Fatigue was used to decrease Q stimulation evoked force (i.e., decreased GTO activation) despite using the same pre-fatigue stimulation currents (i.e., same antidromic recurrent inhibition input). Thus, a decrease in heteronymous inhibition after Q fatigue and a linear relation between stimulation-evoked torque and inhibition both before and after fatigue would support mechanical activation of GTOs as a source of inhibition. A reduction in evoked torque but no change in inhibition would support recurrent inhibition. After fatigue, Q stimulation-evoked knee torque, heteronymous inhibition magnitude, and inhibition duration were significantly decreased for all stimulation intensities. In addition, heteronymous inhibition magnitude was linearly related to twitch-evoked knee torque before and after fatigue. These findings support mechanical activation of GTOs as a source of heteronymous inhibition along with recurrent inhibition. The unique patterns of heteronymous inhibition before and after fatigue across participants suggest the relative contribution of GTOs and recurrent inhibition may vary across persons.