Quantifying the Stiffness of Achilles Tendon: Intra- and Inter-Operator Reliability and the Effect of Ankle Joint Motion.

BACKGROUND The objectives of the present study were to examine the intra- and inter-operator reliability of the MyotonPRO device in quantifying the stiffness of the Achilles tendon and the device's ability to examine the modulation in stiffness of the Achilles tendon during ankle joint flexion. MATERIAL AND METHODS Twenty asymptomatic participants (10 males and 10 females; mean age: 25.0±3.1 years) were recruited for this study. The stiffness of the Achilles tendon was quantified using the MyotonPRO device. RESULTS The results revealed excellent intra- and inter-operator reliability for quantifying Achilles tendon stiffness with the ankle joint in a neutral position and detected a 13.9% increase in stiffness of the Achilles tendon between 0° and 30° of ankle joint flexion. The minimal detectable change (MDC) in tendon stiffness was 45 Newton/meter (N/m). CONCLUSIONS Our findings indicated that the MyotonPRO device is a feasible method to quantify the stiffness of the Achilles tendon and monitor its changes. Thus, it is an essential tool to use to examine the modulation in the stiffness of the Achilles tendon due to pathology or interventions for future studies.