Intersegmental Modulation of Lower-Limb Corticospinal Excitability and Inhibition Induced by Upper-Limb Isometric...

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Intersegmental neural modulation describes how activating one limb affects remote motor areas.
• Previous studies suggest upper-limb contractions influence lower-limb motor excitability, but findings lack consistency.

Purpose of the Study:

• To systematically review evidence on upper-limb isometric contractions' effects on lower-limb motor representations in healthy adults.
• To clarify corticospinal excitability and inhibitory mechanisms modulated by upper-limb contractions.

Main Methods:

• Systematic review following PRISMA 2020 guidelines across major scientific databases.
• Included studies on healthy adults (18-65 years) performing upper-limb isometric contractions (%MVC).
• Assessed lower-limb corticospinal excitability and intracortical/interhemispheric inhibition using transcranial magnetic stimulation.

Main Results:

• Seventeen studies (n=351) met inclusion criteria.
• Most studies showed increased lower-limb motor evoked potential amplitude during upper-limb contractions (≥70% MVC).
• Short-interval intracortical inhibition decreased, indicating motor cortex disinhibition; interhemispheric inhibition results were inconsistent.

Conclusions:

• Upper-limb isometric contractions consistently facilitate lower-limb corticospinal excitability and reduce intracortical inhibition.
• Methodological heterogeneity complicates effect magnitude interpretation.
• Standardized protocols are needed to elucidate intensity-response relationships and neurophysiological mechanisms.