Knee and hip strength measurements obtained by a hand-held dynamometer stabilized by a belt and an examiner demonstrate parallel reliability but not agreement

Objectives: To verify the intrasession reliability and the agreement between strength measurement of hip and knee muscles using hand-held dynamometer stabilized by a belt or by an examiner.

Design: Test-retest design.

Setting: Knee and hip muscles strength were measured bilaterally using hand-held dynamometer stabilized by a belt and by an examiner.

Participants: 24 young and healthy participants.

Main outcome measures: The reliability was verified by the intraclass correlation coefficient_2,1 and the standard error of measurement. Agreement between stabilization methods was verified by the Bland Altman's method.

Results: Reliability was excellent for all muscle groups when stabilized by a belt (intraclass correlation coefficient = 0.78 to 0.95) and by the examiner (intraclass correlation coefficient = 0.83 to 0.97); standard error of measurement ranged between 1kgf to 4kgf at both methods, but they are proportionally lower when stabilized by the examiner. No agreement between both methods was identified for all knee strength measurements and for bilateral hip flexion, right internal and external rotation and left adduction.

Conclusions: The hand-held dynamometer is reliable for hip and knee strength evaluation despite of the stabilization method. However, for the majority of the movements, greater strength and lower error are expected when the examiner stabilizes it.