Interlimb communication to the knee flexors during walking in humans

Area of Science:

• Neuroscience
• Human Locomotion
• Motor Control

Background:

• Symmetric gait and environmental adaptation rely on interlimb coordination.
• Quadriceps muscle receptors influence ipsilateral muscles, with contralateral spinal connections observed in animal models.

Purpose of the Study:

• To determine if contralateral reflex connections exist in humans.
• To identify the neural pathways involved in these interlimb reflexes during locomotion.

Main Methods:

• Investigated contralateral reflex responses in the right biceps femoris (cBF) muscle during walking.
• Applied unexpected unilateral knee joint rotations (flexion/extension).
• Used transcranial magnetic and electrical stimulation to probe for transcortical pathway involvement.

Main Results:

• Strong cBF reflex responses (76 ± 6 ms latency) were evoked by ipsilateral knee extension during late stance.
• Facilitation of motor evoked potentials via transcranial magnetic stimulation, but not electrical, indicated a transcortical contribution.
• The response suggests integration with other sensory inputs for flexible motor control.

Conclusions:

• Contralateral reflex responses from knee extension exist in humans, involving a transcortical pathway.
• This interlimb reflex may prepare the contralateral leg for load bearing, enhancing dynamic stability during walking.
• The findings offer insights into neural mechanisms underlying human gait control and adaptation.