Muscle weakness detected by Maximal Voluntary Isometric Contractions may go undetected by Manual Muscle Testing in men with Spinal Bulbar Muscular Atrophy

Authors

• S Gonzalez-Hernandez
• YS Mukouyama

Abstract

Manual Muscle Testing (MMT) is the most common clinical strength assessment. Drawbacks of MMT include poor sensitivity for strong muscles, subjective grading, and examiner stature influence. Alternatively, Maximal Voluntary Isometric Contraction (MVIC) provides precise measurement for all strength levels, but is costly and time-consuming. MMT and MVIC have not been compared in Spinal and Bulbar Muscular Atrophy (SBMA), a progressive neuromuscular disease characterized by muscle weakness. This study compared MMT and MVIC testing in 44 adult men (53y ± 10y) with SBMA.

Eight bilateral muscles were tested: elbow flexors, elbow extensors, shoulder abductors, knee extensors, hip abductors, hip extensors, hip flexors, and ankle dorsiflexors. MMT was scored on a 10-point scale. MVIC was converted into percent of predicted strength using normative equations. Correlations were run between strength tests and quality of life/functional measures: Short Form 36 Questionnaire, Activities of Daily Living, Two Minute Walk Test, and Adult Myopathy Assessment Tool.

All muscles combined, MVIC revealed more weakness than MMT (MVIC mean 50.6% of predicted, MMT mean 8.9/10). Notably, for knee extensors, hip abductors, and ankle dorsiflexors, ‚â• 75% of patients scored 10/10 on MMT, but had an average of only 35-55% of predicted strength. MMT did not correlate with MVIC. Correlations between strength and quality of life/functional measures were stronger for MVIC than MMT.

In this population, MMT did not detect significant muscle weakness, therefore clinicians should not interpret an MMT score of 10 as “healthy”. MVIC more accurately identified weakness and correlated with function, allowing for earlier intervention strategies.

Scientific Focus Area: Clinical Research

This page was last updated on Monday, September 25, 2023