Muscle Architecture vs Alfredson Protocol in Achilles Tendinopathy

Official title

The Effects of a Muscle Architecture-Based Exercise Program and the Alfredson Protocol on Muscle-Tendon Architecture and Physical Performance in Subjects With Achilles Tendinopathy

Overview

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.

Detailed description

Achilles tendinopathy is an overuse injury that develops as a result of repetitive microtrauma and is commonly observed in athletes as well as in sedentary male individuals. The clinical presentation is typically characterized by localized pain in the mid-portion of the tendon, tenderness, morning stiffness, and symptoms exacerbated by activity. Structurally, the condition is associated with tendon thickening, reduced echogenicity, and disorganization of collagen alignment . As the pathology becomes chronic, a marked decline in functional capacity is observed, which negatively affects both athletic performance and quality of life.

Conservative management is recommended as the first line of treatment, with the eccentric exercise protocol being the most widely used approach. Developed by Alfredson et al. (1998), this protocol consists of performing three sets of fifteen repetitions twice daily, aiming to stimulate collagen synthesis by mechanically loading the tendon. However, studies have shown that this protocol is not effective in every case; in some individuals, symptoms persist, and because the loading scheme is standardized, it fails to account for inter-individual variability. As an alternative, the Heavy Slow Resistance (HSR) exercise protocol, which includes both eccentric and concentric contractions, is applied three times per week. By incorporating controlled, high-resistance, slow-tempo loading, it aims to achieve functional recovery. Studies by Beyer et al. (2015) demonstrated that the HSR protocol yields clinical outcomes comparable to those of the Alfredson protocol, with higher patient satisfaction and compliance. In addition, the protocol developed by Silbernagel et al. (2007) incorporates both eccentric and concentric loading as well as functional activities in a more progressive model. By tailoring exercises to symptom tolerance during the acute and subacute phases and integrating plyometric activities such as hopping and jumping in the later stages, this protocol adopts a function-oriented perspective. Other conservative interventions, including extracorporeal shock wave therapy, cryotherapy, transverse friction massage, and footwear modifications, may provide symptomatic relief; however, their contribution to tendon remodeling is limited, and they do not ensure long-term structural or functional recovery. Although the Alfredson, HSR, and Silbernagel protocols are clinically effective, they carry significant limitations as they are not designed with muscle architecture-specific loading strategies.

The triceps surae muscle group exhibits heterogeneity in terms of architecture and function: the soleus muscle, with relatively short fascicle length, large cross-sectional area, and high pennation angle, contributes primarily to stability and endurance; the medial gastrocnemius is involved in both stability and controlled force generation; and the lateral gastrocnemius, with long fascicles and a narrow pennation angle, plays a key role in explosive force production. Despite these structural differences, both HSR and Silbernagel protocols apply a uniform loading strategy across all triceps surae muscles. For instance, optimal activation of the soleus requires the knee to be flexed, whereas activation of the medial and lateral gastrocnemius requires knee extension. Some existing protocols fail to consider such joint positioning, which may result in deviations from the optimal contraction axis, thereby reducing the effectiveness of muscle activation. This limitation may create uncertainty in the distribution of loading stimuli, hindering adequate tissue adaptation.

The muscle architecture-based exercise program to be implemented in this study is specifically designed in accordance with the architectural characteristics of each muscle, with the aim of providing the most optimal stimulus for each. Muscle and tendon architecture will be assessed using ultrasonography; strength outcomes will be measured with an isokinetic dynamometer; and functional performance will be evaluated through the Single-Leg Balance Test, Single-Leg Forward Hop Test, and Weight-Bearing Lunge Test. In addition, pain will be assessed using the VAS (Visual Analog Scale), and functional status will be measured with the VISA-A questionnaire. By conducting a comparative analysis, this study aims to evaluate the effects of architecture-based loading relative to classical protocols, thereby offering a novel perspective for treatment.

In light of this information, the present randomized controlled experimental trial has been designed to compare the effects of a muscle architecture-based exercise program with the classical Alfredson protocol on muscle-tendon architecture, muscle strength and endurance, functional performance, and symptomatic outcomes in individuals diagnosed with non-insertional Achilles tendinopathy.

Interventions

• Other Muscle Architecture-Based Exercise Program
  Participants 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.
• Other Alfredson Protocol
  This 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

Primary outcome measures

• Muscle Strength and Endurance - Cybex HUMAC/NORM Isokinetic Dynamometer [Time frame: From enrollment to the end of treatment at 12 weeks]
• Muscle and Tendon Architecture Measurements [Time frame: From enrollment to the end of treatment at 12 weeks]
• Function - Victorian Institute of Sport Assessment-Achilles (VISA-A) [Time frame: From enrollment to the end of treatment at 12 weeks]
• Muscle Elasticity - Myoton PRO [Time frame: From enrollment to the end of treatment at 12 weeks]
• Single Leg Forward Hop Distance (cm) [Time frame: From enrollment to the end of treatment at 12 weeks]
• Single Leg Stance Balance Time (seconds) [Time frame: From enrollment to the end of treatment at 12 weeks]
• Ankle Mobility - Weight-Bearing Lunge Test [Time frame: From enrollment to the end of treatment at 12 weeks]

Secondary outcome measures (1)

• Pain - Numeric Rating Scale (NRS) [Time frame: From enrollment to the end of treatment at 12 weeks]

Eligibility criteria

Inclusion criteria

• 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
• Voluntary participation in the study with signed informed consent

Exclusion criteria

• 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)
• Presence of neurological disorders (e.g., peripheral neuropathy, central nervous system disorders)
• Prior experience with eccentric exercise protocols targeting the Achilles tendon
• Acute onset of symptoms suggestive of a tendon rupture

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Treatment

Study locations

Turkey (Türkiye) · 2 centers

• İstanbul University — Istanbul
• İstanbul University — Istanbul

Publications

• Al-Uzri, M., O'Neill, S., Watson, P., & Kelly, C. (2016). Reliability of isokinetic dynamometry of the plantarflexors in knee flexion and extension. Physiotherapy practice and research, 38(1), 49-57.
• O'Neill S, Barry S, Watson P. Plantarflexor strength and endurance deficits associated with mid-portion Achilles tendinopathy: The role of soleus. Phys Ther Sport. 2019 May;37:69-76. doi: 10.1016/j.ptsp.2019.03.002. Epub 2019 Mar 9. PMID 30884279
• Del Bano-Aledo ME, Martinez-Paya JJ, Rios-Diaz J, Mejias-Suarez S, Serrano-Carmona S, de Groot-Ferrando A. Ultrasound measures of tendon thickness: Intra-rater, Inter-rater and Inter-machine reliability. Muscles Ligaments Tendons J. 2017 May 10;7(1):192-199. doi: 10.11138/mltj/2017.7.1.192. eCollection 2017 Jan-Mar. PMID 28717629
• Lauber B, Lichtwark GA, Cresswell AG. Reciprocal activation of gastrocnemius and soleus motor units is associated with fascicle length change during knee flexion. Physiol Rep. 2014 Jun 11;2(6):e12044. doi: 10.14814/phy2.12044. Print 2014 Jun 1. PMID 24920126
• Kwah LK, Pinto RZ, Diong J, Herbert RD. Reliability and validity of ultrasound measurements of muscle fascicle length and pennation in humans: a systematic review. J Appl Physiol (1985). 2013 Mar 15;114(6):761-9. doi: 10.1152/japplphysiol.01430.2011. Epub 2013 Jan 10. PMID 23305989
• Phillips B, Buchholtz K, Burgess TL. Gastrocnemius muscle architecture in distance runners with and without Achilles tendinopathy. S Afr J Sports Med. 2022 Jan 1;34(1):v34i1a12576. doi: 10.17159/2078-516X/2022/v34i1a12576. eCollection 2022. PMID 36815930
• Beyer R, Kongsgaard M, Hougs Kjaer B, Ohlenschlaeger T, Kjaer M, Magnusson SP. Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy: A Randomized Controlled Trial. Am J Sports Med. 2015 Jul;43(7):1704-11. doi: 10.1177/0363546515584760. Epub 2015 May 27. PMID 26018970
• Alfredson H, Pietila T, Jonsson P, Lorentzon R. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med. 1998 May-Jun;26(3):360-6. doi: 10.1177/03635465980260030301. PMID 9617396

Identifiers

NCT: NCT07178418 · Muscle Architecture

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗