Analysis of Surface EMG Signals in Isometric Contraction at Different Angles Using Rainflow Counting Algorithms

Area of Science:

• Biomechanics
• Neuroscience
• Sports Science

Background:

• Muscle strengthening and endurance are crucial for fitness, sports, and prosthetics.
• Understanding the relationship between muscle activity and joint angles is key to optimizing performance.
• The biceps brachii muscle plays a vital role in elbow joint stability during flexion and extension.

Purpose of the Study:

• To analyze isometric contractions of the biceps brachii muscle at different elbow joint angles.
• To introduce and evaluate a new feature, cycle crossing intensity (CCI), derived from surface electromyography (sEMG) signals.
• To assess the statistical significance of CCI in differentiating muscle activity across various elbow flexion angles.

Main Methods:

• Surface electromyography (sEMG) signals were recorded from the biceps brachii of 20 healthy subjects.
• Subjects performed isometric contractions using a 6kg dumbbell at elbow angles of 30°, 60°, and 90°.
• Preprocessed sEMG data were analyzed using the rainflow counting algorithm to calculate CCI and its peak intensity.

Main Results:

• Cycle crossing intensity (CCI) values were distinct for each tested elbow flexion angle.
• CCI magnitude increased with greater elbow flexion angles, with average peak intensities of 425 (30°), 1073 (60°), and 2336 (90°).
• The CCI feature demonstrated high statistical significance for 30°-90° and 60°-90° elbow flexion ranges.

Conclusions:

• The developed CCI feature effectively quantifies differences in biceps brachii muscle activity during isometric contractions at various elbow angles.
• This sEMG-based analysis provides a valuable tool for understanding muscle behavior across the range of elbow joint motion.
• The technique holds potential for application in assessing muscle function in neuromuscular conditions like fatigue.