Obtaining maximum muscle excitation for normalizing shoulder electromyography in dynamic contractions

Area of Science:

• Biomechanics
• Human Movement Science
• Exercise Physiology

Background:

• Maximal voluntary isometric contractions (MVIC) are standard for normalizing electromyographic signals (EMG).
• The suitability of MVIC for normalizing EMG during dynamic contractions is debated.
• Accurate EMG normalization is crucial for understanding muscle function during movement.

Purpose of the Study:

• To compare EMG amplitude normalization methods for dynamic shoulder muscle contractions.
• To evaluate the effectiveness of different maximal voluntary contraction types for EMG normalization.
• To determine the optimal method for normalizing dynamic EMG data.

Main Methods:

• Shoulder muscle EMG was recorded during manually resisted MVICs and maximum voluntary dynamic concentric contractions (MVDC).
• Dynamic contractions included isokinetic testing and manual bi-rotation of a tilted wheel at high velocity (120°/s).
• EMG data from the wheel task was normalized to MVIC, MVICALL, MVDC, and maximum experimental excitation (MEE).

Main Results:

• EMG normalization to muscle-specific MVIC resulted in up to 45% greater mean EMG values compared to normalization using MEE.
• Seventy-five percent of MEEs were observed during dynamic concentric contractions (MVDCs).
• Significant differences in normalized EMG were found across various normalization methods.

Conclusions:

• Normalizing dynamic shoulder EMG to muscle-specific isometric contractions can overestimate muscle activation.
• Maximum experimental excitation (MEE), often occurring during dynamic contractions, is a more representative normalization strategy.
• This study proposes an effective process for obtaining maximal shoulder muscle excitation for accurate dynamic EMG normalization.