Reduced cortical voluntary activation during bilateral knee extension.

Area of Science:

• Exercise Physiology
• Neuroscience
• Biomechanics

Background:

• The bilateral deficit phenomenon, where bilateral contractions yield less force than unilateral ones, is often attributed to reduced neural drive.
• Understanding the neural control of voluntary movements is crucial for optimizing training and rehabilitation.

Purpose of the Study:

• To investigate changes in voluntary activation during bilateral knee extensions.
• To compare voluntary activation assessed via peripheral nerve stimulation and transcranial magnetic stimulation.

Main Methods:

• Fourteen participants performed unilateral and bilateral knee extensions.
• Voluntary activation was assessed using superimposed femoral nerve electrical stimulation (VA_FNES) and transcranial magnetic stimulation (VA_TMS).

Main Results:

• Maximal voluntary contraction (MVC) force was not different between unilateral and bilateral knee extensions.
• A significant reduction in VA_FNES (-2.1±2.4%) and VA_TMS (-1.6±2.7%) was observed during bilateral contractions.

Conclusions:

• Despite no change in MVC force, neural activation is reduced during bilateral knee extensions.
• Counterbalancing mechanisms may mask the decrease in voluntary activation during bilateral contractions.