Grade 4 in manual muscle testing: the problem with submaximal strength assessment

Area of Science:

• Biomechanics
• Human Physiology
• Musculoskeletal Research

Background:

• Muscle strength is crucial for limb support and movement.
• Manual muscle testing (MMT) is a common clinical assessment tool.
• Understanding the relationship between static strength and dynamic capacity is important for accurate assessment.

Purpose of the Study:

• To compare the static muscle force required to support limb segments against gravity with the maximal dynamic force muscle groups can generate.
• To evaluate the functional implications of muscle strength ratios in different joints.

Main Methods:

• Theoretical calculations based on anthropometric data for both sexes.
• Comparison of estimated anti-gravity static muscular moments (MGM) with published isokinetic strength data (MIM).
• Analysis of MGM/MIM ratios across shoulder, elbow, hip, and knee joints.

Main Results:

• The ratio of static to dynamic moment (MGM/MIM) was significantly higher for proximal joints (shoulder, hip) than distal joints (elbow, knee).
• In women, MGM/MIM ratios were 7-27% (shoulder), 5-65% (hip), 7% (elbow), and 5-10% (knee).
• In men, MGM/MIM ratios were 7-21% (shoulder), 4-44% (hip), 8-10% (elbow), and 5-8% (knee).
• Hip abductors, flexors, and extensors showed higher MGM/MIM ratios in women than men.

Conclusions:

• Muscles assessed as MMT grade 4 may utilize only 10% of maximal strength for elbow/knee and 20-40% for shoulder/hip.
• MMT grade 4 is not a valid criterion for setting muscle strength conditioning targets or accurately measuring impairment.
• Limited human sensory precision in force perception further complicates quantitative strength assessment.