Validity and reproducibility of the Jamar dynamometer in children aged 4 – 11 years

PURPOSE: Validity and reproducibility of the Jamar dynamometer were evaluated in children aged 4-11 years. METHOD: Hand grip strength was measured on the dominant side and non-dominant side in 67 patients who had been referred to our specialist centre in the past 3 years because of suspected myopathy. All the patients had had muscle biopsy. Sixteen out of the 67 patients proved to have myopathy, while 51 had no myopathy. The investigator was blinded against the true diagnosis and clinical course of the patients at the time of testing. Validity was assessed by the power to discriminate between patients with and without myopathy, using logistic regression analysis and receiver operating characteristic (ROC) analysis. The area under the ROC curve (AUC) was calculated as a measure of the discriminative power. Sensitivity (Se) and specificity (Sp) were assessed at a specifically chosen cut-off point. Reproducibility was assessed by evaluating the test-retest reliability in a stratified random sample of 40 patients who returned for remeasurements, using the intraclass correlation coefficient (ICC). RESULTS: AUCs ranged from 0.78 - 0.82. At an Se = 81% cut-off point, Sp varied from 67-73%. ICCs ranged from 0.91-0.93. CONCLUSIONS: The Jamar dynamometer had discriminative power in children with suspected myopathy. Reproducibility was high. The Jamar dynamometer was a good, but not completely accurate, test for myopathy.