Sixty physically active patients (aged 18-45) with chronic mid-portion Achilles tendinopathy will be recruited to take part in the study. The patients will be diagnosed by a sports medicine doctor and an MRI scan and will be experiencing palpable Achilles pain at the time of inclusion. The patients will be randomized into either a group performing the Silbernagel combined concentric-eccentric program, or a group performing a novel multi-phase program with specific outcome measures. The study will assess the patients calf strength, reactive strength and running biomechanics at baseline, week's 6 and 12 of a rehabilitation program and be available for a 6 month, 12 month and 2 year follow-up interview. The VISA-A questionnaire will be the primary outcome measure and will be completed at each testing and follow-up session.

Achilles tendinopathy is an overuse injury commonly seen in sports and physical activities that involve running, jumping and hopping. Patients with Achilles tendinopathy experience pain, morning stiffness and reduced ability to exercise. This condition can last for several years in some cases.

Exercise therapy in the form of resistance training has been demonstrated to be the most effective rehabilitation tool to reduce pain and increase function in patients with Achilles tendinopathy. Patients often experience clinical improvements before any meaningful structural changes on MRI or ultrasound imaging are observed. Returning athletes back to competitive sport requires a progressive loading program to enable them to tolerate high stretch-shortening cycle loads appropriate to the demands of their sport.

The SSC6 rehabilitation program is a six-stage pathway with a focus on strength development of the local muscle-tendon unit and the kinetic chain, the development of power and kinetic strength, running biomechanics and running load modification. The progression through each phase is guided by objective outcome criteria based on pain and function, strength and performance tests and achieving individualised resistance load targets. The strength and power exercises are performed at high intensity three days per week with 48 hours recovery. The Silbernagel program is a four-phase involves a daily exercise program of lower intensity with progression through each phase guided by symptoms and function.

This study will compare the effectiveness of a comprehensive Achilles tendinopathy rehabilitation program with progression criteria with a common Achilles tendinopathy rehabilitation program. Sixty recreationally-active subjects aged between 18-45 years who meet the inclusion criteria, will be recruited to partake in this study. The subjects will be randomly assigned to one of two groups where they will undergo a multi-phase rehabilitation program. Data will be collected at baseline, 6 weeks and 12 weeks, to monitor pain and functional response, biomechanical and structural changes. At 6, 12 and 24 months following the commencement of the rehabilitation program, patients will be required to complete a follow-up questionnaire to monitor progress and any re-injury incidence that may have occurred.

The following testing protocols will be performed:

1. VISA-A Questionnaire The VISA-A questionnaire has been shown to be a valid, reliable and easy to use outcome measure tool for intervention studies on Achilles tendinopathy. It consists of eight questions regarding pain and function during both daily living and sporting activities. The overall score is between 0-100 where higher scores represent reduced pain and improved function. An improvement of 21 points between 2 and 12 weeks of a rehabilitation program have been typically observed. The difference in VISA-A score between both training protocols from baseline testing to the outcome testing at 6 weeks, 12 weeks, 6 and 12 months; will formulate the primary outcome measure for this study.
2. Ankle isokinetic testing Achilles tendinopathy has been associated with reduced plantar flexor strength. Isokinetic testing is commonly used to measure plantarflexor peak torque. The subjects will perform 2 isokinetic tests. In the first test the subjects will lie in a prone position in an isokinetic dynamometer with full knee extension and the foot securely strapped to a pedal a neutral ankle position (tibia perpendicular to the sole of the foot). The centre of rotation of the ankle axis will be aligned with the dynamometer. Subjects will be asked to perform a warm-up involving 5 sub maximal concentric plantarflexion and dorsiflexion contractions between 60-100% of their self-perceived MVC. The subjects will then be required to produce a maximal plantarflexion force 5 repetitions for 2 sets with a 1 minute rest between sets. In the second test the subjects will lie in supine position with the knee flexed to 80º in order to specifically test the peak torque of the soleus. The same warm-up protocol and sets and repetitions as the previous test will apply. Both tests will use a speed of 60º per second and operate through an ankle range of between 30º plantarflexion and 20º dorsiflexion.
3. Running biomechanics Altered running biomechanics and muscle recruitment strategies have been highlighted in runners with Achilles tendinopathy. The subjects will be asked to run on the treadmill at a self-selected sub maximal speed. Using 3D motion analysis (Run 3D, Oxford, United Kingdom), a number of biomechanical variables will be measured. These include: vertical and leg stiffness, contact time, flight time, stride length, stride frequency and joint angular displacements from initial contact to mid stance phase.
4. Hop testing Achilles tendon material properties contribute to stretch shortening cycle performance during hopping tasks. Reduced tendon mechanical properties, plantar flexor muscle rate of force development and deficits on a single leg horizontal hop have previously been observed in patients with Achilles tendinopathy. Jump height, ground contact time and reactive strength index (RSI) will be measured using a double and single leg drop jump. Vertical, leg and ankle joint stiffness will be calculated using a novel single leg hurdle hop test. A pilot study has previously been carried out on 10 healthy subjects prior to the commencement of the Achilles RCT study. Good to excellent reliability was found for of vertical stiffness, contact time, ground reaction force, hop distance and rebound distance and 3 trials were sufficient to obtain a true measure of performance across most variables.
5. Subjective questionnaire After the completion of the rehabilitation program patients will be ask to provide feedback on the prescribed program and will complete a training diary where compliance and adherence to the program will be monitored.

Inclusion Criteria:

• Diagnosed with mid-portion Achilles Tendinopathy by a sports medicine physician
• Have experienced symptoms for more than 3 months and less than 3 years
• Aged between 18-45 years,
• Regularly perform running-based exercise more than twice per week

Exclusion Criteria:

• Have a co-existing lower limb injury.
• Have had another running-related injury in the previous 12 months.
• Have had an Achilles injection in the past 6 months