Stretch reflex sensitivity: effects of postural and muscle length changes

Area of Science:

• Neurology
• Biomedical Engineering
• Rehabilitation Science

Background:

• Spasticity is a common motor disorder in multiple sclerosis (MS).
• Understanding spasticity's mechanisms under different conditions is crucial for effective management.
• Current assessments may not fully capture the complexity of spasticity.

Purpose of the Study:

• To investigate changes in spasticity sensitivity and mechanisms in multiple sclerosis patients.
• To evaluate the influence of postural variations on spasticity.
• To explore the role of biomechanical and neural factors in spasticity.

Main Methods:

• Clinical evaluation using the Ashworth scale.
• Laboratory testing including the pendulum test under different postures (supine vs. sitting).
• Neuromusculoskeletal model simulation of spasticity.

Main Results:

• Spasticity, measured by the pendulum test, increased in the supine posture compared to sitting.
• Three distinct stretch reflex response patterns were observed.
• Increased rectus femoris stretch in supine posture contributed to spasticity, but modeling revealed complex factors, including supraspinal descending modulation.

Conclusions:

• Postural control and supraspinal descending modulation play a significant role in spasticity severity in MS.
• Biomechanical spasticity testing should incorporate multiple postures and simultaneous muscle activity monitoring.
• Neuromusculoskeletal models are valuable tools for elucidating the neural mechanisms of spasticity.