Phase-dependent reflex reversal in human leg muscles during walking

Area of Science:

• Neuroscience
• Human Physiology
• Biomechanics

Background:

• Reflex responses are crucial for maintaining balance and adapting to uneven terrain during locomotion.
• Previous studies have primarily investigated reflexes during standing, with limited understanding of dynamic changes during walking.

Purpose of the Study:

• To investigate reflex responses in leg muscles during human walking.
• To identify changes in reflex direction (excitation vs. inhibition) during the gait cycle.
• To compare reflex responses during walking with those during standing.

Main Methods:

• Stimulation of the tibial nerve at the ankle in human subjects during walking and standing.
• Monitoring M-wave from intrinsic foot muscles to control stimulus intensity.
• Electromyographic recording of ipsilateral tibialis anterior (TA), soleus (SO), and rectus femoris (RF) muscles.

Main Results:

• Reproducible middle-latency reflexes (50-90 ms) were observed in TA, SO, and RF muscles during walking, likely of cutaneous origin.
• A novel reversal from reflex excitation to inhibition within single muscles was documented during walking, observed across all subjects and muscles.
• This reflex reversal was not elicited during standing; instead, a consistent inhibition was observed, similar to responses during the stance phase of walking.

Conclusions:

• Human walking involves dynamic reflex modulation, including a previously undocumented excitation-to-inhibition reversal in leg muscles.
• Standing and walking utilize distinct reflex pathways, despite sharing common movement goals.
• These findings advance our understanding of sensorimotor control during human locomotion.