Reliability and Asymmetry Associated with Different Plantar Flexion Assessments Using a Portable Fixed Dynamometer

Background Decreased plantar flexion strength has been linked to several lower limb injuries such as ankle sprains, Achilles tendon ruptures and calf muscle strains. Therefore, it would seem important to assess and monitor an individual’s plantar flexion strength. Aims The purpose of this study was to, 1) quantify the intra- and inter-session reliability of a portable fixed dynamometer (PFD) for measuring peak force (PF) and peak RFD (PRFD) during two dynamic plantar flexion assessments, and 2) determine the inter-limb and inter-protocol asymmetries for PF and PRFD. Methods Eleven participants completed both neutral and maximal dorsi-flexed movements over three testing sessions separated by seven days. Results Good to excellent relative consistency (intraclass correlation coefficients – ICC) and acceptable absolute intra- and inter-session reliability (coefficient of variation – CV) was observed for PF during both protocols (ICC = 0.90–0.99, CV = 1.6–5.3%). Poor to moderate intra- and inter-session reliability was observed for PRFD measures during both protocols (ICC = 0.48–0.96, CV = 5.7–27.0%). There were no differences between left and right legs except for PRFD for the neutral position ( p  < 0.05, ES = -0.82). There were significant differences between protocols, with the neutral position producing higher force outputs ( p  < 0.01, 6.44–66.22%, ES = 1.05–1.75). Conclusions It appears that PFD can be used to reliably measure PF during two dynamic plantar flexion protocols in a healthy male population, however the results from the different protocols cannot be used inter-changeably.