Achilles tendinopathy is a frequent overuse disorder caused by repetitive loading of the tendon, particularly observed in athletes and middle-aged men. It is typically characterized by mid-portion pain, stiffness in the morning, and functional limitations, with structural alterations such as thickening and disrupted collagen alignment. Chronic progression often compromises performance and quality of life.
Eccentric training protocols, such as the Alfredson regimen, are commonly prescribed but their standardized nature does not fully address individual variability. Alternative approaches including Heavy Slow Resistance training and progressive loading models (e.g., Silbernagel protocol) have demonstrated clinical effectiveness and higher patient adherence, yet they still apply uniform loading across the triceps surae without accounting for architectural differences.
Given the heterogeneous structure of the soleus and gastrocnemii, targeted loading strategies may be required to optimize tendon adaptation. To address this, the present study employs a muscle architecture-based exercise program tailored to the functional and structural properties of each muscle. Ultrasound imaging will be used to evaluate muscle-tendon morphology, while isokinetic dynamometry and functional performance tests will quantify outcomes. Pain (VAS) and functional capacity (VISA-A) will also be assessed.
This randomized controlled trial aims to compare the effectiveness of an architecture-specific program with the Alfredson protocol on tendon remodeling, strength, endurance, functional performance, and symptom reduction in individuals with non-insertional Achilles tendinopathy.
Presence of pain and tenderness in the mid-portion of the Achilles tendon (2-6 cm proximal to the insertion) persisting for at least 3 months
Clinical diagnosis of non-insertional Achilles tendinopathy
Pain aggravated by physical activity
Palpable tenderness localized to the mid-portion of the tendon
Diagnosis of insertional Achilles tendinopathy
History of surgery or fracture in the affected lower limb within the past 12 months
Corticosteroid injection to the Achilles tendon within the past month
Presence of systemic diseases (e.g., diabetes mellitus, rheumatoid arthritis)
Parallel
Muscle Architecture-Based Exercise Program
Other interventionParticipants in this arm will perform exercises specifically designed according to the architectural and functional properties of the triceps surae muscles. For example, knee-flexed positions will be used to target the soleus, while knee-extended positions will be emphasized for the gastrocnemii. Loading intensity and exercise progression will be tailored to optimize tendon and muscle remodeling.
Alfredson Protocol
Other interventionThis intervention involves the traditional eccentric heel-drop program, originally developed for mid-portion Achilles tendinopathy. Participants perform three sets of 15 repetitions, twice daily, throughout the intervention period. Exercises are carried out both with the knee extended and flexed to load different portions of the triceps surae. The protocol applies repetitive eccentric loading to the Achilles tendon with the aim of stimulating collagen synthesis, reducing symptoms, and promoting tendon adaptation.
Muscle Strength and Endurance - Cybex HUMAC/NORM Isokinetic Dynamometer
Lower limb plantar flexor strength and endurance will be assessed using the Cybex HUMAC/NORM 2002 isokinetic dynamometer. Participants will be seated securely in the test chair, with trunk and pelvis stabilized by straps.The ankle joint will be aligned with the dynamometer axis at the lateral malleolus, starting in 0° plantargrade neutral. Range of motion will be set between 20° dorsiflexion and 30° plantar flexion, and participants will wear flat-soled shoes. Three test protocols will be applied: Soleus-dominant assessment: knee flexed at 80-90°, concentric mode, angular velocity 90°/s, 20 consecutive repetitions; outcome: peak torque (Nm) Eccentric-concentric assessment: knee extended, eccentric-concentric mode, velocity 90°/s, 3 maximal repetitions; outcome: peak torque (Nm). Combined gastrocnemius-soleus assessment: knee extended, concentric-concentric mode, velocity 180°/s outcome: peak torque (Nm).
Muscle and Tendon Architecture Measurements
Muscle architecture of the medial and lateral gastrocnemius and soleus will be assessed with B-mode ultrasonography. Outcomes include fascicle length (cm), pennation angle (°), thickness (mm), cross-sectional area (cm²), and volume (cm³). Participants will be prone with standardized alignment; images will be acquired using a 5-12 MHz probe in longitudinal and transverse planes. Muscle thickness will be measured between aponeuroses, fascicle length measured directly or calculated, pennation angle determined from fascicle-aponeurosis intersection, CSA traced from transverse images, and volume calculated from serial CSA values. Image analysis will be performed using ImageJ. Achilles tendon will be evaluated with a 10-15 MHz probe in prone with slight knee flexion. Outcomes include tendon thickness (mm, 3 cm proximal to insertion), fibrillar organization scored qualitatively, and neovascularization graded via Power Doppler. All measurements will be obtained by blinded experienced examiner
Function - Victorian Institute of Sport Assessment-Achilles (VISA-A)
The VISA-A is an 8-item, self-reported questionnaire specifically developed to assess symptoms related to Achilles tendinopathy. Scores range from 0 to 100, with higher values indicating better clinical status. The scale has been demonstrated to be a valid and reliable tool for evaluating the clinical severity of Achilles tendinopathy. The Turkish version (VISA-A-Tr) has also shown high test-retest reliability and acceptable internal consistency, confirming its suitability for use in this population.
Muscle Elasticity - Myoton PRO
Muscle and tendon elasticity will be assessed with the MyotonPRO device in prone position with ankles in neutral. The probe applies a brief mechanical impulse, and five measurements per site will be averaged. Measurements will be obtained at the medial gastrocnemius, lateral gastrocnemius, soleus, and Achilles tendon. Separate outcomes will be reported for each parameter: frequency (Hz), stiffness (N/m), decrement (logarithmic), creep (µm/N), and relaxation time (ms). This method provides reliable and reproducible data on tissue mechanical properties.
Pain - Numeric Rating Scale (NRS)
Pain intensity will be assessed using the 3-stage Numeric Rating Scale. Participants will rate their "worst pain," "least pain," and "current pain" experienced in the past 24 hours on a scale from 0 to 10. The mean of these three values will be recorded as the overall pain score. The NRS is a widely used, valid, and reliable tool for quantifying pain in musculoskeletal conditions.
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Halic University
Lead sponsor
Istanbul University
Collaborator
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