Shoulder muscle force and electromyography activity during make versus break tests

Area of Science:

• Biomechanics
• Kinesiology
• Clinical Assessment

Background:

• Shoulder muscle force is clinically assessed using isometric "make" tests or examiner-resisted "break" tests.
• Understanding the force discrepancies between these testing methods is crucial for accurate clinical evaluation.

Purpose of the Study:

• To elucidate the differences in shoulder muscle force production between isometric "make" and "break" testing protocols.
• To compare muscle activity (EMG) during both testing modalities.

Main Methods:

• 25 subjects performed isometric shoulder external rotation and elevation tests.
• Peak isometric and break forces were measured, alongside surface EMG of the infraspinatus and middle deltoid.
• Paired t-tests compared force and EMG data between the "make" and "break" conditions.

Main Results:

• Peak break force was significantly greater than isometric force for both external rotation (46.9%) and elevation (63%).
• Infraspinatus EMG was significantly higher during the break test for external rotation (17.0%).
• Middle deltoid EMG showed a non-significant increase during the break test for elevation.

Conclusions:

• A notable difference exists in both force output and muscle activity between "make" and "break" shoulder tests.
• Clinicians should standardize their force measurement techniques, recognizing that break tests elicit maximal force.
• Greater force during break tests is likely attributed to brief eccentric contractions rather than enhanced muscle recruitment.