This group will receive the standard first-line treatment, which consists of education and progressive exercise-based rehabilitation tailored to the patient. The exercises will be performed once a day and the intensity and number of repetitions will be based on the patients' status. The progressive exercise program is designed to avoid exacerbating the patient's symptoms; however, some pain is permitted during the sessions following the pain monitoring model proposed by Thomee (1997) where the pain is allowed to reach a level of 5 on the Visual Analog Scale during exercises, provided that it diminishes immediately after the session. This pain should subside by the following morning and the pain and stiffness in the Achilles tendon are not permitted to increase from one day to the next.

The intervention group will be given the high volume image-guided injection only once at the beginning of the trial, together with the same education and progressive exercise-based rehabilitation as the control group. The participants will be informed to rest for the first three days and then start slowly the progressive exercises on the same principle as for the control group.

High volume image guided injection consists of 9.5ml of bupivacaine, 0.5ml 20mg Depo-medrol, and 40ml of injectable saline. This procedure will be commenced with a thorough disinfection of the injection site. The mid-portion of the Achilles tendon will then be imaged in the short axis to obtain a cross-sectional view of the tendon, alongside the anterior region, including Kager's fat pad, particularly in areas of maximal pain and increased neovascularity. Once the needle is correctly positioned, the high-volume fluid will be infiltrated under pressure, with ultrasound guidance confirming the reduction or complete disappearance of neovascularisation.

Dynamic stiffness measured using the MyotonPRO at the middle part of the free tendon and over the soleus tendinous junction as identified by ultrasonography in both short and long axis.

The questionnaire encompasses three key domains: pain, functional capacity, and activity level, thereby providing a comprehensive assessment of the patient's condition from their perspective. The Victorian Institute of Sport Assessment - Achilles score ranges from 0 to 100, with 0 indicating no activity and maximum pain, while a score of 100 represents the highest level of activity with no pain experienced. A minimal detectable change of 12 points was considered for the change to be clinically significant (McCormack et al., 2015).

The single-leg heel raise test was utilised to assess the strength and endurance of the plantar flexor muscles. Participants were instructed to lift their heel to the maximum possible height for up to 25 repetitions or until the onset of discomfort or pain, whichever occurred first. A metronome was used to provide auditory feedback to help maintain a consistent pace throughout the test. A successful trial of the single-leg heel raise (SLHR) was recorded if the patient was able to maintain the set pace with the metronome (60 bpm/30 repetitions per minute) and demonstrated proper plantarflexion height and alignment. The trial was considered invalid if the patient compensated by:

• flexing the knee,
• using a hip propulsive strategy,
• or losing vertical displacement due to trunk flexion (Hébert-Losier et al., 2022; Hebert-Losier et al., 2017).

Patients were asked to report any co-interventions undertaken during the 3-month period