Hip Abductor and Knee Extensor Muscle Strength of Children with and without Down Syndrome

The purposes of this study were to 1) determine test-retest reliability of hand-held dynamometer measurements of right hip abductor and knee extensor muscle strength in children with Down syndrome (DS), 2) identify differences in isometric muscle strength between children with DS and peers who are developing typically, and 3) determine the relationship between various anthropometric and demographic variables and isometric muscle strength.

Seventeen children with DS between the ages of seven and 15 years and a comparison group of 17 age- and gender-matched peers who were developing typically participated in the study. A hand-held dynamometer was used to measure peak force during maximal isometric right hip abduction and knee extension at two test sessions approximately one week apart. Peak torque values were calculated by multiplying peak force measurements by the appropriate segment lengths. Anthropometric measurements were obtained, and a questionnaire was used to measure habitual physical activity levels.

Test-retest reliability was high, with intraclass correlation coefficients ranging from 0.89 to 0.95. Children with DS had significantly lower mean peak torque values for hip abduction and knee extension than children in the comparison group. Regression analyses indicated that weight, body mass index, height, activity level, and gender were significant predictors of peak torque production for the sample as a whole.

Hand-held dynamometry can be used to obtain reliable measurements of isometric muscle strength in children with DS. Anthropometric characteristics and activity levels may play a role in peak torque production in children with and without DS.