Submaximal contractions can serve as a reliable technique for shoulder electromyography normalization.

Area of Science:

• Biomechanics
• Neuroscience
• Physiology

Background:

• Electromyography (EMG) data normalization is crucial for comparing muscle activity.
• Maximal voluntary contraction (MVC) is the standard normalization method but is not always practical.
• Alternative normalization techniques are needed for diverse clinical and research scenarios.

Purpose of the Study:

• To evaluate the reliability of electromyography (EMG) data normalization using standardized submaximal contractions.
• To compare the reliability of submaximal normalization across different muscles and force percentages.
• To determine the viability of submaximal normalization when MVC is impractical.

Main Methods:

• Twenty healthy subjects (10 male, 10 female) participated in the study.
• Surface and fine-wire electromyography were used to record muscle activity.
• Data were collected over two sessions at 15%, 30%, 45%, and 60% of day 1 maximum force, with testing repeated after an average of 5.3 days.

Main Results:

• Intraclass correlation coefficient (ICC) and standard error of measurement (SEM) values indicated varying reliability across submaximal percentages for different muscles.
• Deltoid heads, upper trapezius, and serratus anterior showed good reliability under at least one submaximal condition.
• Latissimus dorsi and supraspinatus demonstrated moderate reliability, while the infraspinatus showed poor reliability across all tested conditions.

Conclusions:

• Electromyography (EMG) amplitude normalization to standardized submaximal contractions is a viable alternative to MVC for many muscles.
• This technique is particularly useful in situations where MVC is impractical or subject to change.
• Muscle-specific reliability should be considered when choosing a submaximal normalization percentage.