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What triggers the continuous muscle activity during upright standing?
Kei Masani1, Dimitry G Sayenko, Albert H Vette
1Lyndhurst Centre, Toronto Rehabilitation Institute, Toronto, ON M4G 3V9, Canada. k.masani@utoronto.ca
Gait & Posture
|July 25, 2012
Summary
Ankle extensor activity during standing is driven by the need to counteract gravity
Area of Science:
- Biomechanics
- Human Physiology
- Motor Control
Background:
- Ankle extensors are crucial for maintaining balance during quiet standing.
- They primarily resist the forward toppling torque caused by gravity.
- Understanding the triggers for continuous muscle activity is key to motor control research.
Purpose of the Study:
- To determine if standing muscle activity is dictated by joint torque requirements or vertical limb load.
- To investigate the role of anti-gravity muscles in bipedal equilibrium.
Main Methods:
- Healthy adults stood on a force plate, with measurements of ankle torque, angle, and lower leg muscle electromyograms.
- A knee support device was used to eliminate ankle torque requirements while maintaining vertical load and posture.
- Comparison of muscle activity between free standing and supported conditions.
Main Results:
- Plantarflexor muscle activity significantly decreased to resting levels when ankle torque demand was removed.
- This attenuation of muscle activity was observed even when vertical load and upright posture were maintained.
- Support of one leg led to reduced activity only in the ipsilateral plantarflexors.
Conclusions:
- Continuous muscle activity in anti-gravity muscles is not determined by vertical limb load.
- The primary driver for this muscle activity is the joint torque required to oppose gravity's toppling effect.
- This finding clarifies the control mechanisms for maintaining upright posture.
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