Relationship of manual muscle testing to objective strength measurements.

This study investigates the relationship between manual muscle test scores (MMT) and quantitative isometric strength measurements (QIS). It also evaluates the implications of that relationship for design of therapeutic trials. Extension and flexion strength at the elbows, hips, and knees of 21 neuromuscular disease patients were tested a total of 26 times utilizing both MMT and QIS testing. Paired data were evaluated with Spearman ranked correlation coefficients, and then QIS was predicted from MMT using Lowess, a consistent form of nonparametric regression. Finally, the implications of the Lowess analysis for designing a therapeutic trial were evaluated. MMT and QIS measurements were significantly correlated in all movements tested. Lowess analysis yielded prediction errors ranging from 16 to 24% of QIS range. Analysis of the sample size needed for a therapeutic trial suggested that a protocol measuring MMT would require more subjects for the same level of statistical significance as a protocol measuring QIS. Since it was not possible to reliably predict QIS values from MMT scores, such conversions are not appropriate for clinical use. This inconsistent relationship between MMT and QIS carries major implications for the design of therapeutic trials. Since therapeutic trials are time consuming, expensive, and most centers do not have large numbers of individuals available, using QIS as an outcome measure is a preferable research design.

Upper extremity functional rating for patients with Duchenne muscular dystrophy.

The corresponding deterioration of upper extremity strength and functional capability with increasing age and the relationship between average strength and function were evaluated in 28 boys with Duchenne muscular dystrophy (DMD). Manual muscle testing (MMT) was used to evaluate strength and the Brooke upper extremity grading scale to rate upper extremity function. Mean MMT was found to relate to age in logarithmic fastion, ie, a 1% increase in age led to a 0.9% decrease in mean MMT. Functional grade (FG) related to age in a more complex fashion, revealing three groups based on age: under age 10, all in FG 1; between ages 10 and 13, concentration in FG 2 through 4; and over age 13, eight of ten in FG 5. Regression analysis did not contribute further useful information. Finally, mean MMT was found to be highly significantly related to FG. The plot of mean MMT against FG revealed an S-shaped curve, with rapidly rising functional grade once an average upper extremity strength of 4w was reached. The Brooke scale appears to be useful in describing upper extremity function among DMD patients, although it may reflect a three-grade rather than a six-grade discrimination capability. In describing the natural history of DMD, this scale demonstrates a pattern of rapid functional deterioration during the early adolescent years. This functional deterioration apparently takes place when the decline in strength reaches a threshold which cannot be compensated by muscle substitutions. At that time function deteriorates along a relatively rapid but undefined course.