Principal component analysis biplot visualization of electromyogram features for submaximal muscle strength grading.

Area of Science:

• Biomedical Engineering
• Rehabilitation Science
• Signal Processing

Background:

• Submaximal muscle strength grading is crucial for monitoring rehabilitation progress, particularly for core back muscles.
• Conventional manual muscle testing (MMT) lacks objectivity and struggles with fine gradations (4-, 4, 4+).
• Electromyogram (EMG) offers quantitative insights, but selecting relevant features for grading remains challenging.

Purpose of the Study:

• To develop and validate a method for selecting optimal EMG features for accurate submaximal muscle strength grading.
• To address the limitations of subjective MMT in assessing core back muscle strength progression.
• To enhance the quantitative assessment of muscle strength during rehabilitation using EMG.

Main Methods:

• Utilized Principal Component Analysis (PCA) biplot visualization for selecting EMG features that capture subtle strength variations.
• Employed Root Mean Square (RMS) EMG and Waveform Length as key features identified through biplot analysis.
• Applied K-means and Gaussian Mixture Model (GMM) clustering for grading submaximal muscle strength (4-, 4, 4+, 5) and compared performance using silhouette scores.

Main Results:

• The proposed feature set (RMS EMG and Waveform Length) combined with GMM clustering achieved the highest accuracy.
• Significant mean Silhouette Index (SI) scores were obtained for key back muscles (Longissimus thoracis, Iliocostalis lumborum).
• High grade-wise SI scores confirmed the method's effectiveness in distinguishing between submaximal strength grades (4-, 4, 4+, 5).

Conclusions:

• The study successfully identified a minimal yet effective set of EMG features for submaximal muscle strength grading.
• PCA biplot visualization provides a robust approach to overcome challenges in selecting appropriate EMG features for core back muscles.
• The proposed method significantly improves the objective assessment and monitoring of muscle strength recovery in clinical settings.