Effects of neuromuscular electrical stimulation on contralateral quadriceps function

Area of Science:

• Neuromuscular Physiology
• Exercise Science
• Rehabilitation Engineering

Background:

• Maximal voluntary strength in knee extensor muscles can be augmented by applying neuromuscular electrical stimulation (NMES) to the contralateral homologous muscle.
• The underlying neural mechanisms and potential intensity-dependent effects of this contralateral facilitation remain incompletely understood.

Purpose of the Study:

• To investigate if concomitant NMES application to the contralateral quadriceps enhances neural drive to the agonist muscles during maximal voluntary contractions (MVCs).
• To examine a potential dose-response relationship between NMES intensity and the degree of contralateral strength facilitation.

Main Methods:

• Twelve healthy men performed MVCs of the left knee extensors under three conditions: low-intensity NMES (10% MVC) to the right quadriceps, high-intensity NMES (30% MVC), or no NMES.
• Voluntary activation was assessed using supramaximal nerve stimulation.
• Electromyography (EMG) of vastus lateralis (VL) and biceps femoris (BF) was recorded.

Main Results:

• MVC torque, voluntary activation, and VL EMG activity were significantly higher with both low- and high-intensity NMES compared to the no-NMES condition (P < .05).
• No significant differences in strength or neural activation were observed between the low- and high-intensity NMES conditions.
• NMES applied to the right quadriceps enhanced MVC strength of the contralateral left knee extensors.

Conclusions:

• Acute NMES of the contralateral quadriceps facilitates maximal voluntary strength of the homologous muscle by enhancing efferent neural drive.
• The observed contralateral facilitation does not appear to be intensity-dependent within the tested range (10-30% MVC).