Quantifying Plantar Flexor Muscles Stiffness During Passive and Active Force Generation Using Shear Wave Elastography...

Area of Science:

• Biomechanics
• Neurology
• Rehabilitation Science

Background:

• Stroke survivors often experience altered muscle mechanical properties, impacting motor function.
• Understanding the specific changes in plantar flexor muscle stiffness is crucial for effective rehabilitation strategies.

Purpose of the Study:

• To investigate the mechanical properties of paretic and healthy plantar flexor muscles.
• To assess the spatial distribution of stiffness between the gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) during active force generation in stroke survivors and healthy controls.

Main Methods:

• Utilized shear wave elastography to measure shear modulus in GM and GL muscles.
• Measurements were taken during passive ankle dorsiflexion and varying levels of maximal voluntary contraction (MVC) in control (CNT) and stroke survivor groups (SSG).
• Evaluated muscle activations of GM, GL, soleus, and tibialis anterior.

Main Results:

• Paretic plantar flexor muscles showed increased passive stiffness with high tension during passive mobilization.
• Paretic plantar flexors exhibited decreased active stiffness levels during submaximal and maximal MVC.
• A discrepancy in stiffness between GM and GL was observed in the passive state, particularly in the SSG, but not during active conditions.

Conclusions:

• Muscle mechanical properties in stroke survivors are differentially affected by the activation state.
• Stiffness distribution among synergistic plantar flexor muscles varies in the passive state but remains consistent during active contractions.