Evoked EMG versus Muscle Torque during Fatiguing Functional Electrical Stimulation-Evoked Muscle Contractions and Short-Term Recovery in Individuals with Spinal Cord Injury

Sensors, 2014 · DOI: 10.3390/s141222907 · Published: December 3, 2014

Spinal Cord Injury Neurology Musculoskeletal Medicine

Simple Explanation

This study explores how muscle torque relates to m-waves (electrical signals from muscles) after brief rests between repeated muscle contractions caused by functional electrical stimulation (FES). FES is used to stimulate muscles in people with spinal cord injuries (SCI). The research looks at whether the connection between muscle torque and m-waves stays consistent after short breaks, during repeated isometric muscle contractions induced by FES in SCI individuals. The study found that even when the same muscle torque was produced, m-wave characteristics changed during the contractions. This suggests that using m-waves to estimate torque during FES exercise in people with SCI can be affected by short recovery periods.

Study Duration

Not specified

Participants

8 male subjects with SCI

Evidence Level

Not specified

Key Findings

1
M-wave amplitude and area increased significantly as muscles fatigued, while the time between the stimulus and the positive peak of the m-wave decreased.
2
M-wave variables recovered faster and more completely than torque after recovery intervals.
3
The relationship between m-waves and torque changes depending on the degree of muscle fatigue, indicating that m-waves cannot be used as a direct proxy for torque estimation during FES exercise with recovery periods.

Research Summary

The study investigated the relationship between muscle torque and m-waves during fatiguing FES-evoked contractions and short-term recovery in individuals with SCI. The results showed that m-wave variables changed progressively throughout the contractions, even when the same muscle torque was generated, and that these variables recovered faster than torque after recovery intervals. The study concluded that short recovery intervals between FES-evoked exercise sessions can interfere with using m-waves as a proxy for torque estimation in individuals with SCI.

Practical Implications

Improved FES Control Strategies

The findings suggest the need for advanced signal processing and control techniques to accurately estimate muscle torque from m-waves during FES, particularly when recovery periods are involved.

Personalized FES Models

The study indicates that FES feedback systems based on m-waves may be more effective if tailored to individual legs or subjects, accounting for variations in the m-wave × torque relationship.

Further Research on Muscle Fatigue

The paper highlights the need for further investigation into the mechanisms of muscle fatigue and recovery in SCI populations to improve the utility of m-waves as a sensor of muscle fatigue during FES-evoked physical activities.

Study Limitations

1
Relatively small sample size (n=8)
2
Potential for large intra-individual difference of m-wave characteristics between subjects
3
Temporal variations within and between m-waves limit their use as a proxy for force or a predictor of fatigue-failure

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