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

Abstract

Objective: To compare the static moment of force required for a muscle group to support a limb segment against gravity with the maximal dynamic moment it can generate. Design: Based on anthropometric measures of both sexes and theoretical calculations, the estimated anti-gravity static muscular moments (MGM) at the shoulder, elbow, hip and knee joints were compared with published data relating to the isokinetic strength (MIM) of the same muscle groups. Results: The ratio of static to dynamic moment, MGM/MIM, was drastically higher in muscles operating on the proximal compared with the more distal joints. In women, the values of this ratio in the shoulder, hip, elbow and knee muscles were 7-27%, 5-65%, 7% and 5-10% respectively. The corresponding figures in men were 7-21 %, 4-44%, 8-10% and 5-8%. The ratios relating to the abductors, flexors and extensors of the hip joint were substantially higher in women than in men. Conclusions: Since MGM and MIM correspond to grades 3 and 5 in manual muscle testing, the findings of this theoretical analysis indicate that elbow and knee muscles assessed as having grade 4 may generate as low as 10% of their maximal strength. With regard to shoulder and hip muscles the corresponding values are typically around 20% and 30-40%. Coupled with the very limited human precision in sensing of force, these findings indicate that where quantitative targets in muscle strength conditioning are set or when an accurate measure of impairment is being sought, grade 4 cannot and should not serve as a valid criterion.