Participants allocated to the Alfredson exercise program were instructed to exercise twice a day on both legs for 12 months. They performed concentric calf rises (CR) on both legs up and eccentric CR on one leg down.

The protocol contained 15 repetitions and 3 sets on each leg with extended and flexed knee. One session contained 45 reps in the flexed position and 45 reps in the extended position, the total daily number of reps was 180. At the start, the exercises were performed with body weight. Participants could progress by adding the 5, 10 and 15 kg, if they met the criteria. The criteria for adding weight was at least one week of training at the same weight and no disabling pain during or after the exercise during the week.

Participants allocated to the Silbernagel exercise program were instructed to exercise every day with exception of the first week (every other day) for 12 months. The protocol contained 4 phases, which were based on a variety of CR exercises.

The protocol contained concentric and eccentric CR on both legs, CR on one leg, CR in sitting, CR on the step, CR without step, quick rebound CR, CR with added weight and hops on the forefoot.

The daily number of reps for 1st phase was 135, for the 2nd phase was 240, for the 3rd phase was 255 and for the 4th phase was 150. It's performed with body weight, added weight and plyometric loading progressively through all phases (maximal added weight is 15 kilos). To progress to the next phase participant needs to reach pain intensity during and after exercise under 5 from the 10 on the visual analogue scale, morning stiffness should not increase as well as pain during the week.

Alfredson eccentric therapeutical protocol.

The VISA-A questionnaire is the most commonly used outcome in clinical trials of Achilles tendinopathy treatment with proven reliability and validity. It consists of eight questions covering pain, function, daily living and sports activities. The score ranges from 0-100 where 0 means disability (impairment of function and pain of Achilles tendon) and 100 represents no disability.

Achilles tendon stiffness (N/m) is a measure of the biomechanical response of the Achilles tendon tissue. Stiffness was assessed by MyotonPro (Myoton AS), which has been shown as a valid and reliable measurement tool of Achilles tendon mechanical properties in the clinical setting.