Validity and reproducibility of hand-held dynamometry in children aged 4-11 years.

Objective: To evaluate validity and reproducibility of hand-held dynamometry in 11 different muscle groups in children.

Design And Patients: Maximum isometric muscle strength was measured with a calibrated hand-held dynamometer in 61 patients aged 4-11 years who had been referred to our specialist centre in the past 3 years because of suspected myopathy. All the patients had had muscle biopsy.

Methods: Validity was assessed by the power to discriminate between patients with and without myopathy, using logistic regression analysis and receiver operating characteristic analysis and sensitivity and specificity at a specifically chosen cut-off point. Reproducibility was evaluated by test-retest reliability in a stratified random sample of 40 patients who returned for re-measurements, using the intraclass correlation coefficient and the standard error of measurement.

Results: In the patients, areas under the receiver operating characteristic curve ranged from 0.66 to 0.88. At a specifically chosen cut-off point, sensitivity varied from 73% to 87%, while specificity varied from 54% to 80%. Intraclass correlation coefficients ranged from 0.73 to 0.91. The standard error of measurement ranged from 3.3 N to 12.2 N.

Conclusion: Performance of hand-held dynamometry varied widely in the 11 muscle groups. Highest performance was observed in the elbow flexors. Test-retest reliability of the mean value of 2 efforts was generally higher than the maximum value.