Development and reliability of a hand-held dynamometer device to measure the ankle dorsiflexor muscle strength

Abstract

Background: Ankle dorsiflexor muscle strength is a crucial component of gait.

Objective: We describe the development of a simple, hand-held dynamometer to measure the ankle dorsiflexor muscle strength in the sitting position. In addition, we examine its intra- and inter-rater reliability.

Methods: Measurements of the peak ankle dorsiflexor muscle strength were obtained by two examiners for 30 ankles of 15 healthy adults at two time points, with a one-day interval between measurements, to determine the inter- and intra-rater reliability. The intraclass correlation coefficients were calculated, and an intraclass correlation coefficient > 0.90 was considered as excellent reliability. A Bland-Altman analysis was used to assess systemic bias. The minimal detectable change in muscle strength was calculated with a confidence level of 95% (MDC₉₅).

Results: The reliability of the device was excellent for both intra- (intraclass correlation coefficients [1,3] = 0.94) and inter-rater (intraclass correlation coefficients [2,3] = 0.96) comparisons. No fixed or proportional bias was observed between the two examiners. The MDC₉₅ was 0.77 N/kg.

Conclusions: Our results indicate the excellent reliability and responsiveness of our device. By obtaining the measurements of dorsiflexor strength while sitting, compensatory motions are suppressed, yielding a more consistent measurement that can be reliably used to detect subtle changes in the ankle dorsiflexor muscle strength.

Keywords: Ankle dorsiflexor muscle strength; compensatory motion; hand-held dynamometer; inter-rater; intra-rater; reliability testing.

Figure 1.

Measurement position for use of the hand-held dynamometer.

Figure 2.

Bland–Altman intra-rater reliability data plot (a) and inter-rater reliability data plot (b).