Are the mechanical properties of Achilles tendon altered in CrossFit athletes? Reliability and accuracy of myotonometry.

Purpose: Tendons adapt to loads affecting them by changing tendons' mechanical and morphological properties. The aim of the study was to investigate the influence of involvement in sport activities in the form of CrossFit training by individuals of different age upon the mechanical properties of Achilles tendon.

Methods: 231 people participated in the study. One group consisted of subjects who trained CrossFit as amateurs, the other group comprised subjects who were not physically active. Achilles tendon was studied for various positions of the ankle joint: 0° DF/PF, 10° DF, 20° DF, 20° PF and 40° PF. The following mechanical and viscoelastic tendon properties were measured using MyotonPRO: frequency [Hz], stiffness [N/m], decrement [log], relaxation time [ms] and creep [De]. The results have been compared in reference to physical activity, BMI, age and length of training history.

Results: Both the tension and stiffness increased with degree of Achilles tendon stretching and decreased as it contracted. Higher values have been noted in the group of people in training and with higher BMI values. The elasticity of Achilles tendon decreased with plantar flexion increase. Lower elasticity has been recorded in the group in training and with higher BMI. No significant influence of age and length of training history upon the parameters achieved has been noted.

Conclusions: The specificity of CrossFit training and accompanying mechanical load result in development of adaptation changes in Achilles tendon, in the form of its higher tone/tension and stiffness, as well as lower elasticity.