Added load increases the peak frequency of intermuscular coherence

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Cortical motor neuron activity influences lower motor neurons via distinct beta (15-30 Hz) and gamma (30-50 Hz) frequency bands.
• The transition dynamics of cortical drive frequency with changing contraction strength remain unclear.

Purpose of the Study:

• To investigate how the frequency of common neuronal drive shifts between synergistic arm muscles as isometric contraction strength increases.
• To determine if the shift in cortical drive frequency is continuous or abrupt with varying loads.

Main Methods:

• Utilized intermuscular coherence (IMC) analysis between synergistic arm muscles (biceps and brachioradialis).
• Recorded surface electromyography (EMG) from nine healthy adults performing isometric holds with varying added loads (0, 3, 5, 10 pounds).
• Calculated IMC across muscle groups during sustained isometric contractions.

Main Results:

• Significant IMC was observed in the 20-50 Hz range across all tested loads.
• Repeated measures ANOVA revealed a significant increase in the peak IMC frequency with added load.
• Peak IMC frequency rose from 32.7 Hz (no load) to 35.3 Hz, 35.7 Hz, and 36.3 Hz with 3, 5, and 10-pound loads, respectively.

Conclusions:

• Increased load during isometric contractions leads to a significant elevation in the peak frequency of intermuscular coherence.
• Findings suggest that cortical drive operates across a spectrum of frequencies, adapting to the demands of isometric contractions against external loads.
• The study provides evidence for a load-dependent modulation of cortical drive frequency during motor tasks.