Excellent Reliability for an Instrumented Test of Ankle Plantarflexion Force

The assessment of ankle plantarflexion force is commonly required in athletic performance and clinical rehabilitation settings to assess the integrity of the calf and lower limb musculature. The force generating capacity of the soleus muscle is thought to be important in many aspects of sporting and everyday function. Unfortunately, there are only a few reliable tests describing the assessment of the strength of the soleus muscle, especially in dorsiflexion greater than plantar grade/neutral which mimics ankle joint positions associated with higher ground contact forces. Accordingly, the purpose of this study is to describe the reliability, feasibility, and clinimetrics of a novel test of plantarflexion force in a clinical setting.

Test-retest reliability of a seated isometric plantar flexion strength test performed a minimum of one day apart (maximum of six) using the maximum value of four trials was investigated using a force plate and custom apparatus in 61 volunteer adults (of varying activity levels (Tegner one to ten). Inter-rater reliability (ICC_2,1), Bland-Altman, and minimal detectable change values were estimated.

Sixty-one subjects were tested (49 male, 12 female, 39.6±12.6 years, 81.1±13.8kg). Excellent test-retest reliability was demonstrated (ICC_2,1)=0.976 [0.97 to 0.98], p<0.001; and minimal detectable change (MDC) was found to be 118N.

Excellent test-retest reliability and a minimal detectable change of 118N (14.8% bodyweight) were demonstrated for this measure of plantar flexion force. MDC data can inform clinical progression and between-limb differences in healthy and injured individuals. Further, these results can be used to explore the clinical importance of the measurement using the instrumentation.

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