ACHILLES - New methods to study Achilles tendon structure and loading

Achilles tendon is an important tissue in locomotion, but human research lacks clinically relevant evidence of tendon structure–function relationships. Animal and cadaver studies have revealed the complex structure of the Achilles tendon (AT) with three subtendons, which is likely a key for understanding individual differences in the function of healthy and pathological tendons. ACHILLES first develops a USTIM-method for mapping the three-dimensional structure of the AT and its three subtendons in vivo, using ultrasonography, kinematics, electrical stimulation and computational modeling. Human experiments are intertwined with modeling of AT subtendons using our newly developed continuum finite beam elements for beam-like soft tissue structures. The experimental data feeds the models that are used to find factors predisposing AT to high regional strains and stresses. Ultimately, ACHILLES produces a REHAB-TRAINING tool to address the need for individualized treatments that can be used to guide rehabilitation. ACHILLES bridges the current gap between in vivo human and cadaver/animal studies in the area of muscle-tendon tissue biomechanics and advances understanding of human AT structure function relationships with the novel tools.

Current information

Volunteer for student helper or intern (unpaid) and gain experience in data analysis! Contact Taija.m.juutinen@jyu.fi for information.

May 2025: We are not actively recruiting anymore, and focus now on data analysis. 

March 2025: First publication on new method to study Achilles subtendon structure https://onlinelibrary.wiley.com/doi/10.1111/sms.70042 

USTIM method was developed in the project

USTIM uses ultrasound, motion analysis and electrical stimulation to examine the subtendon structure of the Achilles tendon (Finni et al. 2025, link above). The measurement is performed in the prone position, where the Achilles tendon is imaged with ultrasound in different positions of the ankle joint. At the same time, the calf muscles are electrically stimulated from the surface of the skin at three different points in turn. The electrical stimulation is performed at very low intensity in short bursts of about one second. This is followed by ultrasound imaging of the tendon during ankle extension in the sitting position with the knee straight and the knee bent.

In USTIM measurements the participant is lying on her stomach while the Achilles tendon is being imaged with ultrasound.

Functional measurements

In functional measurements, EMG electrodes are placed on the skin of the legs to measure the electrical activity of the muscles along with reflective markers for motion imaging. At the same time, the Achilles tendon is imaged using ultrasound. During the measurements, the subject will be asked to walk, perform heel raises and drops in a seated and standing position on both one and two legs, do bilateral squats, and jumps. If you have a tension injury, you will only do as much as you can safely do in normal life. The purpose of the measurements is to determine the function and load on the tendon during different movements.  

Tendon force measurements using shear wave tensiometry

For subsample of participants, we applied shear wave tensiometry for assessing Achilles tendon forces and compared it against estimations from kinematic and kinetic analysis. In tendon force measurements, a device is attached around the ankle to measure the strength of the Achilles tendon from the skin surface. The rest of the measurement is similar to the functional measurements described above, where the subject is asked to run, walk, jump, and perform various rehabilitation exercises.

Questionnaire validation study 

Cross-cultural adaptation into the Finnish language is being carried out for the Achilles Tendon Total Rupture score (ATRS) and Tendinopathy Severity of the Achilles (TENDINS-A) questionnaires.