Achilles tendinopathy (AT) is one of the most common overuse injuries in runners, with an estimated incidence ranging from 0.6% to 18.5% of all running-related injuries, reaching up to 52% in elite runners. Its prevalence increases significantly from the fourth decade of life due to histological changes associated with aging, such as tissue degeneration, decreased vascularization, alterations in collagen structure, reduced recovery capacity, and increased tendon stiffness. The repetitive nature of running and the high proportion of the population practicing this sport make runners, especially those over 40 years old, a particularly vulnerable group.

The etiology of AT is multifactorial and includes biomechanical, physiological, and contextual factors. Major risk factors include sudden increases in load, planning errors in training, biomechanical alterations, overweight, metabolic comorbidities such as diabetes or dyslipidemia, and exposure to certain medications, especially corticosteroids and fluoroquinolones. In middle-aged individuals, the combination of intrinsic and extrinsic factors along with structural tendon changes explains both the higher prevalence and the worse prognosis observed in this population.

Physiotherapy is one of the preferred treatments for AT, with therapeutic exercise-particularly the Alfredson protocol-being the intervention with the strongest scientific support. Despite its efficacy, between 25% and 45% of patients do not achieve full recovery, suggesting the influence of clinical, personal, and contextual factors not always considered in studies. Additionally, there is high variability in return-to-sport times, which has led to the development of specific programs for runners over 40.

In the Aragón community, there are no studies describing the extent of AT in senior runners nor systematically analyzing their clinical characteristics, comorbidities, referral patterns, or healthcare service use. This lack of information hampers evidence-based decision-making and the planning of preventive and therapeutic strategies in physiotherapy. This study aims to fill this gap by providing contextualized information to improve clinical practice, healthcare pathways, and physiotherapeutic guidelines.

The hypothesis of the study is that an assessment system using screening has validity for detecting clinical changes in senior runners with Achilles tendon pain. The main objective is to determine the validity of this screening compared to other clinical measures after applying a physiotherapy protocol.

A clinimetric validity design is proposed. The sample will include 40 runners over 40 years old, belonging to sports clubs, who train at least three days a week and have participated in at least five 10 km races in the past year. Participants will be recruited through running clubs and social media, and randomly assigned to two groups of 20 people each. Exclusion criteria include recent invasive treatments, use of fluoroquinolones in the last year, autoimmune diseases, or difficulties understanding questionnaires.

Data collected will include sociodemographic, anthropometric, sports activity, and clinical variables through validated scales (VISA-A, NPRS, IPAQ, and SMFA), as well as ultrasound characteristics of the tendon, ankle mobility, passive calcaneal mobility, and functional screening tests based on active movements and jumps.

The procedure involves initial measurements, random assignment to control or experimental groups, and a 12-week home self-treatment program. Both groups will perform the Alfredson exercise protocol and receive health education; the experimental group will add analytical stretching of the posterior chain following OMT methodology.

Statistical analysis will assess intergroup and intragroup differences using repeated measures ANOVA, analyze time-group interactions, and include sensitivity-to-change statistics such as effect size, minimal clinically important difference, and reliable change index.

A gender perspective will be incorporated, limiting the representation of one sex to a maximum of 70% of the sample and analyzing results separately by gender. Main limitations include the small sample size, short follow-up duration, and limited control over adherence to home treatment.

Finally, the study clearly defines internal and external validity and clarifies the use of the term screening as a functional discrimination tool within a homogeneous and clinically defined population, without asserting generalization to the broader population.

Inclusion Criteria:

• Senior runners
• They belong to a running club
• That they have run at least 5 10-kilometer races in the past year
• They should work out at least three times a week

Exclusion Criteria:

• Runners who have received physiotherapy treatment involving invasive techniques in the last 3 months
• Runners who have received pharmacological treatment with fluoroquinolones (levofloxacin, ciprofloxacin) in the last year
• Runners with autoimmune diseases
• Individuals with limited comprehension who may be unable to answer surveys

This study collects clinical and functional information from patients with Achilles tendinopathy, including demographic data, pain measures, functional tests, and patient-reported outcomes. However, the informed consent for this trial does not include permission for secondary use or external sharing of de-identified individual data.

In addition, the purpose of the study is to evaluate two specific physiotherapy-based intervention programs, and the dataset is not intended for broader data-sharing or secondary analyses outside the primary research group.