[Recurrent inhibition during Jendrassik maneuver]

Area of Science:

• Neuroscience
• Human Physiology
• Motor Control

Background:

• The Jendrassik maneuver is known to enhance reflex responses.
• The precise mechanism behind this enhancement, particularly its effect on recurrent inhibition, remains debated.
• Understanding these mechanisms is crucial for interpreting reflex studies and neurological conditions.

Purpose of the Study:

• To investigate whether vigorous handgrip, as part of the Jendrassik maneuver, alters recurrent inhibition of soleus motoneurons.
• To differentiate between changes in motoneuron excitability and recurrent inhibition during the maneuver.

Main Methods:

• Soleus H-reflex was elicited using tibial nerve stimulation in 28 healthy volunteers.
• Measurements were taken at rest and during bilateral vigorous handgrip.
• Paired stimulation techniques with varying interstimulus intervals were employed to assess H1 and H2 waves.
• H-reflex amplitudes were quantified relative to the maximal M-wave amplitude.

Main Results:

• Vigorous handgrip significantly increased the maximal H-reflex amplitude (H1max) compared to rest.
• The maximal conditioned H2 wave amplitude (H2max), reflecting both excitability and inhibition, was significantly higher during handgrip.
• The minimal conditioned H2 wave amplitude (H2), reflecting only recurrent inhibition, showed no significant difference between handgrip and rest conditions.

Conclusions:

• The enhancement of the soleus H-reflex during the Jendrassik maneuver is primarily due to increased motoneuron excitability.
• Recurrent inhibition acting on soleus alpha motoneurons is maintained during remote muscle contraction (handgrip).
• The Jendrassik maneuver does not decrease recurrent inhibition; rather, increased motoneuron excitability drives the reflex potentiation.