The study was withdrawn prior to enrollment. The objectives of this study were incorporated into a broader registered and completed study, making this record redundant and no longer necessary to maintain as a separate entry.

This work is designed as a prospective cohort study, in which the effects of a protocol of 12-week resistance training loading the Achilles tendon in patients with Achilles tendinopathy (AT) will be monitored. It is estimated that at least 20 patients will participate. In addition, there will be a small control group of healthy participants which will not complete the same protocol, but will be monitored for natural changes in same objectives. Group of patients will be instructed to perform a training protocol.

The research within one participant will last a total of 26 weeks from the initial to the final examination and will include control measurements at 6 and 12 weeks from the beginning of therapy. Potential participants will be selected based on the recommendation of a specialist doctor and their suitability will be assessed according to the inclusion criteria. They will then be invited to an initial examination. This will include an objective examination by a physiotherapist, a subjective assessment by the patient and an ultrasonographic (USG) examination followed by a micromorphological analysis using special software. At the end of the initial examination, the participant will be informed about training protocol.

Inclusion Criteria:

• the patient shows symptoms of Achilles tendinopathy (pain, swelling and dysfunction in the area of Achilles tendon), which at least partially limit his quality of life during normal or sporting activities,
• the patient is in the age group of 18-60 years,
• the patient has difficulties in only one lower limb; the second, asymptomatic limb will be considered the reference,
• the patient is not aware of any mechanical damage to the tendon in symptomatic limb in the past (e.g. partial or complete rupture as a result of an injury),
• the patient has not undergone any treatment aimed at AS in the last 3 months (surgery, corticoid application, plasma therapy, shock waves, physiotherapy, etc.), objective US examination of AS shows structural changes (expansion, neovascularization, focal hypoechoic areas, etc.).

Exclusion Criteria:

• patient has been diagnosed with a rheumatic disease or a disease of the central nervous system
• patient is aware of mechanical damage to the Achilles tendon as a result of an injury in the past.