Fatigue during functional neuromuscular stimulation

Area of Science:

• Neurology
• Biomedical Engineering
• Rehabilitation Science

Background:

• Muscle fatigue limits the effectiveness of functional neuromuscular stimulation (FNS).
• Understanding fatigue parameters during intermittent stimulation is essential for optimizing FNS protocols.
• Previous research has not fully elucidated the impact of intermittent stimulation on fatigue.

Purpose of the Study:

• To compare muscle fatigue generated by continuous electrical stimulation versus intermittent stimulation schemes.
• To investigate how fatigue parameters are influenced by different stimulation patterns in T5-T6 paraplegics.
• To develop a model for FNS controllers that accounts for fatigue-induced non-stationarity.

Main Methods:

• Experiments were conducted on T5-T6 paraplegics using both continuous and intermittent electrical stimulation.
• Torque development over time was measured and analyzed using exponential time constants.
• Average torque over time was calculated for intermittent stimulation to estimate fatigue parameters.

Main Results:

• Continuous stimulation resulted in torque decay described by a double exponential, with a falling time constant of 100-200 sec.
• Intermittent stimulation markedly postponed fatigue, with torque time courses also following a double exponential.
• Fatigue led to a decline in average muscle torque to a patient-specific constant level, independent of the stimulation duty cycle.

Conclusions:

• Intermittent electrical stimulation is a viable strategy to mitigate muscle fatigue in FNS applications.
• The developed model accurately estimates fatigue parameters and can inform the design of adaptive FNS controllers.
• Findings provide insights into managing non-stationarity caused by fatigue in neuromuscular electrical stimulation.