Publications

• MyotonPRO has excellent reliability in measuring the tendon and muscle stiffness.
• Stiffness of Achilles tendon and gastrocnemius muscle is higher in males.
• Tension effect in tendon and muscle stiffness is similar in both genders.

Purpose: The purpose of the present study was to investigate sex-related differences in the stiffness of the Achilles tendon and gastrocnemius muscle at rest and tensioned state. Another purpose of the study was to investigate the inter-observer reliability and inter- day repeatability of MyotonPRO, a portable myotonometer, in measuring tendon and muscle stiffness.

Methods: The study included 73 healthy participants (19 males for the reliability and repeatability study; 24 males and 30 females for the experimental study) with an age range of 19-27 years. The stiffness of the Achilles tendon and medial gastrocnemius muscle was measured with a portable myotonometer (MyotonPRO, Muomeetria Ltd., Tallinn, Estonia). The stiffness measurements of the Achilles tendon and medial gastrocnemius muscle were performed at 0° and 10° of ankle joint dorsiflexion. The stiffness measurements were performed by two physiotherapists to determine the inter-observer reliability of the device. For the interday repeatability (or between-day precision), the same individuals were reassessed by the same examiner after a 3-day interval.

Results: It was found that MyotonPRO has excellent inter-observer reliability and inter-day repeatability in measuring the stiffness of the Achilles tendon and medial gastrocnemius muscle (ICC=0.83-0.98). The stiffness of the Achilles tendon and gastrocnemius muscle at neutral and 10° joint dorsiflexion was higher in males compared to females (p<0.05); however, the stiffness value of difference between neutral and 10º joint dorsiflexion for the Achilles tendon and gastrocnemius muscle was similar in both groups (p>0.05).

Discussion: The obtained results suggest that MyotonPRO is a reliable and repeatable device in measuring the stiffness of the Achilles tendon and gastrocnemius muscle. Furthermore, males have stiffer Achilles tendon and gastrocnemius muscle, compared to females; however, the change in the stiffness of the assessed tissues caused by joint motion was similar in both sexes.

Keywords: Achilles tendon; gastrocnemius muscle; sex; stiffness; myotonometer; reliability.

It was found that males have stiffer Achilles tendon and gastrocnemius muscle compared to females; however, changes in the stiffness of the assessed tissues caused by joint motion were similar in both sexes. Lower tendon and muscle stiffness in females may cause the impaired joint stability and/or control compared to males, and it may cause an increase in the musculoskeletal injury risk in females. On the other hand, the obtained results suggest that MyotonPRO has excellent inter-observer reliability and inter-day repeatability in measuring the stiffness of the Achilles tendon and medial gastrocnemius muscle.

Brief summary