Maximal isometric strength on the kinetic communicator system for Duchenne muscular dystrophy patients.

Abstract

The purpose of this study was to create a quantitative muscle strength reference for the knee extensors, ankle plantar flexors, elbow extensors and elbow flexors for Duchenne Muscular Dystrophy (DMD) patients from age six to fifteen. The second purpose was to determine the relationship of maximal isometric contractile force between the left and the right sides of the four muscle groups.

Two hundred and fourteen DMD boys were tested isometrically using the Kinetic Communicator system. The best six measurements in each muscle group on both sides of the body were obtained. The average of the best six measurements was defined as the maximal isometric contractile force for each individual. An average maximal isometric contractile force for individual muscle groups was computed for each age. Ninety-five percent confidence intervals for the mean scores of each muscle group in each age group of DMDs were calculated. A paired comparison t test was used to compare the maximal isometric force between the left and the right sides of the four muscle groups. Maximum and minimum scores in each age group were determined. Linear regression equation models were built to predict the muscle deterioration rate for all DMD subjects. Predicted maximal isometric forces for all subjects from age six to fifteen were calculated using the simple linear regression equations. All predicted values were referred to the normative references in maximal isometric force for DMD patients.

The results showed that maximal isometric force was significantly correlated with age in DMD patients. A negative linear regression relationship was significant between age and maximal isometric force at the .01 level for knee extensors, elbow extensors and elbow flexors. It was significant at the .05 level on ankle plantar flexors. Knee extensors lost 26.4% of their isometric strength each year of age. Elbow extensors lost 3.2% of their force per year, and a 10.9% muscle force loss was seen for elbow flexors a year. The force deterioration on ankle plantar flexors was predicted at 2.2% each year. The data in this study indicated that muscle force declined with age for the knee extensors and the elbow flexors. The relationship between age and muscle force is not as strong for the ankle plantar flexors and elbow extensors. The comparison between the left and the right sides of the four muscle groups revealed that there were no statistically significant differences for knee extensors (p = .904), ankle plantar flexors (p = .319), elbow extensors (p = .055), and elbow flexors (p = .172). Combining right and left muscle groups, the linear regression equations for these four muscle groups are shown in the following: LNYke=4.615- 0.169age; LNYpf=5.13-0.03409 age; LNYee=3.31-0.04018age; LNYef=3.723-0.08883 age. .