Ultrasound Echogenicity as an Indicator of Muscle Fatigue during Functional Electrical Stimulation

Area of Science:

• Biomedical Engineering
• Rehabilitation Technology
• Neuroscience

Background:

• Functional electrical stimulation (FES) aids mobility in neurological conditions but is limited by rapid muscle fatigue.
• Developing reliable methods to detect FES-induced muscle fatigue is crucial for effective neurorehabilitation.

Purpose of the Study:

• To investigate ultrasound (US) imaging-derived echogenicity as a sensitive indicator of FES-induced muscle fatigue.
• To assess the correlation between US echogenicity and muscle fatigue under isometric and dynamic conditions.

Main Methods:

• Eight non-disabled participants underwent FES on their tibialis anterior (TA) muscles during isometric and dynamic ankle dorsiflexion.
• Synchronously collected data included ankle torque/angle, US echogenicity signals from TA, and stimulation intensity.
• Analyzed the relative change in US echogenicity (ERC) in relation to muscle fatigue progression.

Main Results:

• US echogenicity relative change (ERC) showed an exponential decrease with progressing fatigue under both isometric (R2=0.891±0.081) and dynamic (R2=0.858±0.065) conditions.
• A strong linear relationship was observed between US ERC and muscle fatigue benchmarks (R2=0.840±0.054 isometric; R2=0.794±0.065 dynamic).

Conclusions:

• US echogenicity is a computationally efficient signal that accurately represents FES-induced muscle fatigue.
• This finding supports the potential for real-time implementation of US echogenicity in FES systems for closed-loop fatigue management.