Shoulder manual muscle resistance test cannot fully detect muscle weakness

Area of Science:

• Orthopedics
• Sports Medicine
• Physical Therapy

Background:

• Manual resistance tests are common for assessing shoulder muscle weakness.
• Previous research has not established thresholds for detecting weakness using these tests.

Purpose of the Study:

• To determine the threshold for muscle weakness detection using shoulder manual resistance tests.
• To establish objective cut-off points for manual assessment of shoulder strength deficits.

Main Methods:

• Fifty-three patients with shoulder injuries (rotator cuff, SLAP, Bankart lesions) underwent manual muscle resistance tests (abduction, external rotation, belly press).
• Subjective weakness was compared to the contralateral shoulder to categorize patients into positive and negative groups.
• Isometric strength was measured with a hand-held dynamometer, and receiver operating characteristic analysis identified cut-off points for side-to-side strength ratios.

Main Results:

• Manual detection of weakness was consistent when strength was below 60% of the contralateral shoulder.
• A mixture of positive and negative results occurred between 60% and 90% strength.
• Specific cut-off points were identified: 78.9% for abduction, 73.8% for external rotation, and 84.0% for belly press tests.

Conclusions:

• Manual shoulder resistance tests can detect side-to-side strength differences when weakness exceeds 15-25% (i.e., strength is <75-85% of the contralateral side).
• Clinicians must recognize the limitations of manual muscle testing, as it may not detect all instances of shoulder muscle weakness.
• Careful consideration of these limitations is crucial for accurate clinical assessment of shoulder function.