Motoneuron persistent inward current contribution to increased torque responses to wide-pulse high-frequency...

Area of Science:

• Neuroscience
• Exercise Physiology
• Rehabilitation Science

Background:

• Neuromuscular electrical stimulation (NMES) is used to improve muscle function.
• Wide-pulse high-frequency (WPHF) NMES aims to enhance muscle activation.
• The role of remote contractions in modulating NMES effects is not fully understood.

Purpose of the Study:

• To investigate the impact of a remote handgrip contraction during WPHF NMES.
• To assess effects on torque production and motoneuron excitability in plantar flexors.
• To estimate the contribution of persistent inward current (PIC) to motoneuron firing.

Main Methods:

• Ten participants performed plantar flexion contractions.
• WPHF NMES was applied with and without a concurrent remote handgrip contraction.
• High-density EMG recorded during contractions to estimate PIC contribution (∆F).

Main Results:

• While extra torque was not significantly increased, sustained EMG activity was higher with remote contraction.
• ∆F, an estimate of PIC contribution, was significantly greater with WPHF NMES plus remote contraction compared to control.
• A positive correlation was observed between ∆F change score and extra torque.

Conclusions:

• Remote muscle contraction during WPHF NMES enhances central drive to the target muscle.
• This enhancement may be mediated by an increased PIC contribution to motoneuron firing.
• Understanding these mechanisms can optimize NMES interventions for improved neuromuscular function.