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Motor Unit Stimulation

Motor Unit Stimulation

When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...

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Related Experiment Video

Updated: Oct 2, 2025

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Published on: September 13, 2015

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

Jennifer Cooper¹, Andrew Karduna¹

¹Department of Human Physiology, University of Oregon, Eugene, OR, United States.

Journal of Biomechanics

|March 1, 2022

Summary

This study found that normalizing electromyography (EMG) data using standardized submaximal contractions offers a reliable alternative when maximal voluntary contractions are impractical. Reliability varied by muscle, but submaximal normalization is a viable technique for most muscles.

Keywords:

Electromyography Kinematics Normalization Shoulder

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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.