Introduction Neuromuscular development is of importance for motor performance. The aim of this study was to evaluate the reliability of instrumented measurements of ankle resistance during passive movements and muscle strength in the lower leg in children. Methods A test-retest design was used with a 2-way mixed-effects model to calculate intraclass correlation coefficients (ICC). Eleven typically developing children (eight girls), aged 7–14 years, participated. Passive ankle resistance was assessed with the NeuroFlexor, which performed controlled passive movements over 40° from plantarflexion to maximal dorsiflexion at slow and fast velocities. A biomechanical model decomposed measured passive ankle resistance (torque) into non-neural (stiffness coefficient) and maximal neural torque (neural resistance) components. Muscle strength was measured using a rig-fixed dynamometer during maximal isometric voluntary contractions of the plantarflexors and dorsiflexors. Testing was performed twice throughout the same day with a 2-hour interval. Results ICC (95% CI) between the two measurements were as follows: stiffness coefficient: 0.79 (0.13,0.94); maximal neural torque: 0.96 (0.86,0.99); maximal voluntary contraction of plantarflexors: 0.96 (0.86, 0.99); and dorsiflexors 0.96 (0.86, 0.99). Conclusion The NeuroFlexor and rig-fixed dynamometer showed good to excellent test-retest reliability for assessing passive ankle joint resistance and muscle strength in typically developing children. Further research is needed to explore their use in clinical populations.
Åhblom et al. (2026) studied this question.