 For this purpose, the laboratory UMR Inserm U930 - CNRS ERL 3106 in Tours has developed a non-invasive ultrasonic device, named Achillus, which, via an ultrasonic probe, allowing to access the viscoelastic properties of the tendon during the contraction of the sural triceps. It is therefore important in the exploratory work we propose to have a proven method of calibration of forces applied to the tendon, which is why an ergometer laboratory biomechanics and bioengineering at UT Compiègne is associated with our experiments. 