Control of upright standing posture during low-frequency linear oscillation

Area of Science:

• Biomechanics
• Human Physiology
• Neuroscience

Background:

• Maintaining upright stance is crucial for daily activities.
• Sensory feedback, including vestibular and proprioceptive inputs, is vital for postural control.
• The role of specific joints and muscle activation patterns during dynamic postural challenges requires further investigation.

Purpose of the Study:

• To investigate the effects of anteroposterior sled movement on human upright standing.
• To analyze body sway, joint kinematics, and muscle electromyographic (EMG) activity during varying acceleration levels.
• To explore the contribution of the ankle joint and neck muscles to postural stability.

Main Methods:

• Six healthy males stood on a sled platform in darkness.
• Sinusoidal anteroposterior acceleration was applied at different magnitudes (0.02–0.08 G) and stroke lengths (6–14 m).
• Body sway, head-neck movement, and lower leg muscle EMG activity were recorded.

Main Results:

• Low acceleration (0.02–0.04 G) induced ankle-driven body sway with tonic EMG activity in lower leg muscles.
• High acceleration (0.06–0.08 G) increased body sway, showing reciprocal muscle activation and marked tonic activation of neck muscles.
• The head remained upright, suggesting the vestibulocollic reflex contributed to neck muscle activation.

Conclusions:

• Anteroposterior sled oscillation causes body sway proportional to acceleration, primarily involving the ankle joint.
• Higher accelerations elicit increased body sway and significant neck muscle activation, indicating a role in head stabilization.
• The vestibulocollic reflex likely plays a role in tonic neck muscle activation during dynamic postural control.