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Randomized Controlled Trial Evaluating the Effects of Long-Hold Yielding Isometric Exercise on Pain, Function, Vascularity, and Mechanical Properties of the Patellar Tendon in Competitive Weightlifting Athletes
Sponsor study identifier
interventional
24
1 country
1
Study Start
February 1, 2027
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
Primary Completion
December 20, 2027
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
Study Completion
April 1, 2028
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
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.
Registry-reported information. Elapsed time and enrollment totals alone do not measure study progress or recruitment pace.
April 1, 2028
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
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Dates and qualifiers reported by the registry. Estimated dates do not confirm that a milestone has occurred.
December 1, 2025
Actual (reported)January 23, 2026
Actual (reported)February 1, 2027
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
December 20, 2027
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
April 1, 2028
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
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
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.
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.
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.
Universidad Complutense de Madrid, Faculty of Nursing, Physiotherapy and Podiatry, Department of Physiotherapy
Madrid, Madrid, 28040, Spain
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.
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.
First Submitted
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)
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)
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.
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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.
December 1, 2025
First Posted
January 23, 2026
Study Start
February 1, 2027
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
Primary Completion
December 20, 2027
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
Study Completion
April 1, 2028
EstimatedPlanned date reported by the registry; this milestone is not confirmed as achieved.
Last Updated
January 23, 2026
Record last verified: 2026-01
De-identified individual participant data (IPD) derived from this study may be shared after completion of the primary analyses and publication of the main results. Shared data will be limited to curated and filtered analytical datasets containing derived quantitative variables used in statistical analyses, such as ultrasound-derived morphology, vascularity and elastography metrics, biomechanical outcomes, and clinical scale scores. Raw data sources, including original imaging files, force recordings and questionnaire forms, will not be shared. All shared datasets will be fully anonymized in compliance with GDPR (EU 2016/679), Spanish LOPDGDD regulations and institutional ethical requirements. Access to de-identified IPD will be provided upon reasonable request, subject to review by the study investigators, and shared through secure institutional or trusted research repositories after publication of the primary study findings.
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