Publications

• This study brings novel insights into the reliability of the MyotonPRO and provides standardized procedures for measuring Achilles tendon stiffness in clinical trials with patients. /…/ Not only does this study show superior reliability outcomes with a standardized seated position, it also demonstrated consistent outcomes between days and weeks.
• Compared to more operator-dependent modalities (e.g., ultrasound elastography), the MyotonPRO requires less specialized training and reduces user-dependent variability. Its portability and straightforward setup make it a convenient tool for researchers and clinicians to measure soft-tissue stiffness quickly and accurately.
• The MyotonPRO provides a convenient and portable solution, particularly in situations where visual imaging is not essential but reliable numerical estimates of tendon stiffness are required.

Objectives: This study evaluates the test-retest reliability and inter-rater reliability of the MyotonPRO for measuring Achilles tendon stiffness at two standardized sites over various time frames and settings.

Methods: Eight healthy participants underwent assessments by three raters over six visits. Tendon stiffness was measured at proximal (mid-portion) and distal (insertional) regions of the Achilles tendon at various time frames (10–15 s, 10–15 min, 24 h, and 14 days apart). Measurements included participant repositioning and two activity stimuli (daily living and sport). Reliability was calculated using the intraclass correlation coefficient (ICC), its 95% confidence interval, coefficient of variation, standard error of measurement, and minimal detectable change.

Results: Short-term reliability (10–15 min) was excellent, with an ICC of 0.956 (0.929–0.974). Between days reliability (24 h) was good, with an ICC of 0.889 (0.802–0.938). Between weeks reliability (2 weeks) was good with an ICC of 0.886 (0.811–0.931). Short-term reliability with the simulation of activity of daily living was good, with an ICC of 0.917 (0.875–0.945). Short-term reliability with the simulation of sport was good with an ICC of 0.933 (0.891–0.96). Between days reliability with the simulation of sport was good, with an ICC of 0.920 (0.859–0.955).

Conclusions: When used in a standardized position, the MyotonPRO demonstrates reliable repeated measurements of Achilles tendon stiffness. This protocol provides a foundation for clinical research and rehabilitation by clarifying expected reliability across minutes, days, and weeks, thus aiding clinicians and researchers in monitoring tendon adaptations and making evidence-based decisions.

Figure 2. Standardized measurement of Achilles tendon stiffness. (A) Sitting position; (B) Measured sites; (C) Foot positioning; (D) MyotonPRO positioning.

Keywords: Achilles tendon, stiffness, reliability, MyotonPRO, tendon

Overall, the MyotonPRO has demonstrated good to excellent reliability when utilizing a standardized participant position and precise positioning of the measuring device on the rack to eliminate any deviations in the angle relative to the measured Achilles tendon. Nevertheless, these findings primarily apply to healthy young adults under controlled conditions, and must be interpreted with caution in clinical scenarios involving older or symptomatic populations. The reliability of the MyotonPRO has been confirmed for the same operator across different days and weeks, as well as between two operators using the same standardized measurement protocol. Within these parameters, the MyotonPRO can be confidently employed to capture tendon stiffness values in a consistent manner. However, additional research is warranted to determine the device’s performance in diverse patient groups and real-world clinical settings.

In conclusion, while these findings underscore the reliability of MyotonPRO measurements for Achilles tendon stiffness in healthy young adults, they should be interpreted with caution when applying them to clinical populations. Future work might explore other sampling sites, employ alternative exercise stimuli, and include symptomatic individuals to better elucidate the MyotonPRO’s full potential in rehabilitation and performance contexts.