Long-Hold Yielding Isometric Exercise for Patellar Tendinopathy in Weightlifting Athletes

NCT07361848 | Not Yet Recruiting

• 1 other identifier: UCM-JAP-QUANTFLOW-26
• Study Type: interventional
• Target: 24
• Locations: 1 country
• Sites: 1

Brief Summary

The goal of this clinical trial is to evaluate whether a long-hold yielding isometric exercise program improves pain, tendon vascularity, mechanical properties, and functional performance in weightlifting athletes with patellar tendinopathy. The study will also explore the safety and feasibility of this exercise strategy. Researchers will compare the long-hold isometric intervention with routine training recommendations to determine its effects on symptoms and tendon function. Participants will perform the supervised isometric protocol and complete pain ratings, functional tests, and ultrasound evaluations of the patellar tendon.

Conditions

Patellar Tendinopathy / Jumpers Knee

Keywords

patellar tendinopathy; long hold yielding isometrics; weightlifting athletes; tendon vascularity; shear-wave elastography; quantitative ultrasound; echotexture; echostructure; ehointensity; echovariation; doppler imaging; tendon stifness; stress-strain curve; young's modulus; biomechanics; jumper's knee; iPulley isokinetic; countermovement jump; force platform biomechanics; tissue mechanical properties; musculoskeletal imaging; clincal trial; randomized controlled trial

Outcome Measures

Primary Outcomes (7)

• Functional Disability (Victorian Institute of Sport Assessment Scale for Tendinopathy, VISA-P Score)

  Patellar tendon-related functional impairment assessed using the Victorian Institute of Sport Assessment for Patellar Tendinopathy (VISA-P) questionnaire (0-100). Higher scores indicate better function. This measure evaluates global clinical improvement and load tolerance in daily living and sports context.

  Baseline, 8 weeks (post-intervention), 12 weeks follow-up, 24 weeks follow up

• Pain During Tendon-Loading Activities (Numeric Pain Rating Scale)

  Pain intensity during tendon-loading activities, such as squatting or jumping, assessed using the Numeric Pain Rating Scale (NPRS, 0-10), where 0 represents no pain and 10 represents the worst pain imaginable. Higher scores indicate greater pain. This outcome reflects symptom severity and clinical response to the intervention.

  Baseline, 8 weeks (post-intervention), 12 weeks follow-up, and 24 weeks follow-up

• Patellar Tendon Vascularity (Surface Area Quantification)

  Quantitative assessment of intratendinous vascularity using Surface Area Quantification (SAQ) derived from power Doppler ultrasound images. Doppler images are processed using image segmentation in Fiji/ImageJ software to isolate Doppler-positive pixels within a predefined tendon region of interest. Vascularity is expressed as the percentage of Doppler-positive pixel area relative to the total tendon area analyzed, with higher percentages indicating greater intratendinous vascularization.

  Baseline and 8 weeks (post-intervention)

• Patellar Tendon Vascularity (Öhberg Score)

  Intratendinous neovascularization assessed using the Öhberg grading scale based on power Doppler ultrasound imaging. The scale ranges from 0 to 4, where 0 indicates absence of Doppler-detected vessels and higher scores indicate increasing degrees of intratendinous neovascularization. Higher scores represent greater vascularity.

  Baseline and 8 weeks (post-intervention)

• Patellar Tendon Vascularity (Modified Öhberg Score)

  Intratendinous neovascularization assessed using the Modified Öhberg grading scale based on power Doppler ultrasound imaging. The scale ranges from 0 to 5, reflecting the proportion and extent of Doppler-detected intratendinous vessels within the region of interest, with higher scores indicating greater vascularity.

  Baseline and 8 weeks (post-intervention)

• Tendon echostructure: Patellar Tendon Cross-Sectional Area (CSA)

  Patellar tendon cross-sectional area (CSA, square millimeters \[mm²\]) will be assessed using transverse B-mode ultrasound imaging. CSA will be measured at three standardized locations along the tendon (proximal, mid-portion, and distal), and the mean value across the three regions will be calculated and used for analysis. CSA reflects tendon morphology and structural adaptation to mechanical loading.

  Baseline, 8 weeks (post-intervention)

• Tendon echostructure: Patellar Tendon Thickness

  Patellar tendon thickness (millimeters \[mm\]) will be measured using longitudinal B-mode ultrasound imaging at three standardized locations along the tendon (proximal, mid-portion, and distal). The mean thickness across the three regions will be calculated and used for analysis. Tendon thickness represents a structural characteristic associated with tendon adaptation and pathological changes.

  Baseline, 8 weeks (post-intervention)

Secondary Outcomes (11)

• Tendon Stiffness (Shear-Wave Elastography in kPa)

  Baseline, 8 weeks (post-intervention)

• Tendon Stiffness (Shear-Wave Velocity)

  Baseline and 8 weeks (post-intervention)

• Tendon Mechanical Properties: Stiffness (iPulley and Ultrasound)

  Baseline, 8 weeks (post-intervention)

• Maximal Isometric Force (IMTP or iPulley)

  Baseline, 8 weeks (post-intervention)

• Tendon Echointensity (B-mode Ultrasound, Echotexture)

  Baseline, 8 weeks (post-intervention)

Study Arms (2)

Long-Hold Yielding Isometrics

EXPERIMENTAL

This arm receives a structured long-hold yielding isometric (LH-YI) exercise program targeting the patellar tendon. Participants perform 3-5 sets of 3-5 repetitions, each consisting of a 30-60 second sustained isometric contraction at a discomfort level of 3-4/10. Exercises are performed three times per week for 8 weeks, using a yielding squat or mid-range knee-flexion isometric position. Load is individualized based on tolerance. One supervised session per week ensures correct technique and monitoring. The protocol aims to improve pain, tendon vascularity, stiffness, and neuromechanical performance through prolonged tendon loading.

Behavioral: Long-Hold Yielding Isometric Exercise Program

Usual-Care Training Condition

ACTIVE COMPARATOR

This arm follows standard training recommendations for patellar tendinopathy without exposure to long-duration isometric loading. Participants maintain their regular weightlifting training with guidance on load management, symptom monitoring, and progressive strengthening. No sustained isometric exercises are permitted. This condition serves as a real-world comparable control to evaluate the specific effects of long-hold yielding isometrics on pain, function, tendon vascularity, stiffness, and neuromechanical performance.

Other: Usual-Care Training Condition

Interventions

Long-Hold Yielding Isometric Exercise Program BEHAVIORAL

The intervention consists of a structured long-hold yielding isometric (LH-YI) loading program targeting the patellar tendon. Participants perform 3-5 sets of 3-5 repetitions, each held for 30-60 seconds at an intensity corresponding to 3-4/10 discomfort. Exercises are executed in a controlled knee-flexion position, either as a yielding squat or machine-assisted isometric hold. Training takes place three times per week for 8 weeks, with one supervised session weekly to ensure correct load, technique, adherence, and safety. The protocol aims to induce mechanotransductive adaptation, reduce pain, modulate tendon vascularity, and improve tendon stiffness and neuromechanical performance.

Also known as: Long-Hold Isometric Loading

Long-Hold Yielding Isometrics

Usual-Care Training Condition OTHER

Participants maintain their regular weightlifting training following standard recommendations for patellar tendinopathy management. This includes load monitoring, symptom-guided progression, avoidance of high-irritability movements, and general strengthening. No long-duration isometric exercises or targeted LH-YI loading are permitted. This condition serves as an active comparator reflecting real-world practice to isolate the specific therapeutic and mechanobiological effects of the long-hold yielding isometric protocol.

Also known as: Standard Tendinopathy Management

Usual-Care Training Condition

Eligibility Criteria

• Age: 18 Years - 45 Years
• Sex: all
• Healthy Volunteers: No
• Age Groups: Adult (18-64)

You may qualify if:

• Competitive weightlifting athletes (Olympic weightlifting or CrossFit) training ≥3 times per week.
• Age 18-45 years.
• Symptom duration of at least 6 weeks.
• Presence of vascularized patellar tendinopathy, defined as Doppler-detectable intratendinous neovascularization using standardized settings.
• VISA-P score \< 80 at baseline.
• Ability to perform loaded lower-limb exercises safely.
• Willingness to refrain from other structured isometric interventions focused on the patellar tendon during the study period.
• Ability to provide informed consent.
• Sex/Gender requirement: both men and women eligible; the study includes sex-stratified analysis to examine potential sex-based differences in tendon response.

You may not qualify if:

• Previous knee surgery within the past 12 months.
• Partial or complete patellar tendon rupture (confirmed clinically or by ultrasound).
• Coexisting knee conditions (e.g., meniscal tear, ACL/PCL injury, patellofemoral joint instability) that significantly affect load tolerance.
• Systemic diseases affecting tendon health (e.g., diabetes, rheumatoid arthritis, connective tissue disorders).
• Corticosteroid injection in the patellar tendon within the last 6 months.
• Participation in other clinical trials involving exercise or tendon-loading interventions.
• Neuromuscular or medical conditions limiting safe performance of isometric or plyometric exercise.
• Pregnancy.
• Inability to commit to follow-up assessments at 8, 12, and 24 weeks.

Sponsors & Collaborators

• Universidad Complutense de Madrid: lead

Study Sites (1)

Universidad Complutense de Madrid, Faculty of Nursing, Physiotherapy and Podiatry, Department of Physiotherapy

Madrid, Madrid, 28040, Spain

Location

Related Publications (3)

• Pringels L, Van Acker G, Wezenbeek E, Burssens A, Vanden Bossche L. Novel Insights Into the Intratendinous Pressure Behavior of the Achilles Tendon in Athletes. Sports Health. 2025 Mar;17(2):374-382. doi: 10.1177/19417381241245357. Epub 2024 Apr 12.

  PMID: 38610105 BACKGROUND

• Scattone Silva R, Song KE, Hullfish TJ, Sprague A, Silbernagel KG, Baxter JR. Patellar Tendon Load Progression during Rehabilitation Exercises: Implications for the Treatment of Patellar Tendon Injuries. Med Sci Sports Exerc. 2024 Mar 1;56(3):545-552. doi: 10.1249/MSS.0000000000003323. Epub 2023 Oct 16.

  PMID: 37847102 BACKGROUND

• Merkel, M. F. R., Hellsten, Y., Magnusson, S. P., and Kjaer, M. 2021. Tendon blood flow, angiogenesis, and tendinopathy pathogenesis. Transl Sports Med 4:756-771. https://doi.org/10.1002/TSM2.280.

  BACKGROUND

Central Study Contacts

Jaime Almazán Polo, Doctor

CONTACT

34 + 652103445; jaalmaza@ucm.es

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Masking Details: Only the outcomes assessors are masked to group allocation. Ultrasound technicians, elastography operators, and biomechanical evaluators remain blinded throughout all assessment time points (T0, T1, T2, T3). Due to the nature of the exercise-based intervention, neither participants nor care providers can be blinded. Investigators responsible for data analysis will work with anonymized, coded datasets to maintain allocation concealment during statistical procedures.
• Purpose: TREATMENT
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Assistant Professor of Physiotherapy and Principal Investigator

Model Details: This study uses a two-arm parallel-group randomized controlled design. Participants are assigned in a 1:1 ratio to either the Long-Hold Yielding Isometric intervention group or the usual-care control group. Randomization is computer-generated with allocation concealment. Outcome assessors for ultrasound imaging, elastography, and biomechanical testing are blinded to group assignment. The intervention lasts 8 weeks, with additional follow-up assessments at 12 and 24 weeks to evaluate durability of effects. The model is designed to compare therapeutic and mechanobiological responses between groups while accounting for sex stratification to explore gender-related differences in tendon adaptation.

Study Record Dates

• First Submitted: December 1, 2025
• First Posted: January 23, 2026
• Study Start (Estimated): February 1, 2027
• Primary Completion (Estimated): December 20, 2027
• Study Completion (Estimated): April 1, 2028
• Last Updated: January 23, 2026

Record last verified: 2026-01

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP, ANALYTIC CODE
• Time Frame: De-identified individual participant data and supporting documents will be made available after publication of the primary study results. Data will remain available for a minimum of five years following initial release.
• Access Criteria: Access to de-identified individual participant data and supporting information will be granted upon reasonable request for research purposes. Requests will be reviewed by the study investigators to assess scientific validity, ethical compliance and alignment with participant consent. Approved requests will receive access to curated and filtered analytical datasets only. Raw data sources, including imaging files and original questionnaires, will not be shared.

Locations

ES (1)