Effects of Isometric, Isotonic, and Eccentric VMO Exercises in Patellofemoral Pain Syndrome (VMO-PFPS)

Comparison of the Effects of Isometric, Isotonic, and Eccentric Vastus Medialis Oblique Strengthening Exercises Applied in Terminal Knee Extension Range on Pain, Function, and Muscle Architecture in Individuals With Patellofemoral Pain Syndrome: A Randomized Controlled Trial

Patellofemoral pain syndrome (PFPS) is a common musculoskeletal condition characterized by anterior knee pain, especially during activities such as stair climbing, squatting, running, and prolonged sitting. Weakness or delayed activation of the vastus medialis oblique (VMO) muscle is considered an important contributing factor in the development of PFPS.

This study aims to compare the effects of three different types of VMO strengthening exercises (isometric, isotonic, and eccentric) applied within the terminal knee extension range (0-30°) on pain, functional performance, and muscle architecture in individuals with PFPS.

Participants will be randomly assigned to one of three exercise groups. All participants will receive a standardized physiotherapy program, including heat therapy, TENS, and therapeutic ultrasound, followed by group-specific VMO strengthening exercises. The intervention will be performed three times per week for 8 weeks.

Outcomes will be assessed before and after the intervention and will include pain intensity (Visual Analog Scale), functional performance (WOMAC, 30-second sit-to-stand test, and stair test), and muscle architecture parameters measured by ultrasound imaging.

The results of this study are expected to provide evidence for optimizing rehabilitation strategies in individuals with PFPS.

Study Overview

• Status: Not yet recruiting
• Conditions: Patellofemoral Pain Syndrome; Anterior Knee Pain
• Intervention / Treatment: Other: Isometric VMO Exercise; Other: Isotonic VMO Exercise; Other: Eccentric VMO Exercise

Detailed Description

Patellofemoral pain syndrome (PFPS) is a prevalent condition affecting physically active individuals and is associated with anterior knee pain during functional activities. Alterations in patellofemoral joint biomechanics, particularly related to quadriceps muscle imbalance and insufficient activation of the vastus medialis oblique (VMO), are considered key contributing factors.

Although VMO strengthening is widely used in clinical practice, there is limited evidence comparing the effects of different contraction types-specifically isometric, isotonic, and eccentric exercises-applied within the terminal knee extension range (0-30°), where patellofemoral joint stress and stabilization demands are highest.

This study is designed as a three-arm, parallel-group, randomized controlled trial to investigate the comparative effects of these exercise modalities on pain, functional outcomes, and muscle architecture. The intervention period will last 8 weeks, with sessions conducted three times per week.

A total of 90 participants aged 18-40 years with clinically diagnosed PFPS will be recruited and randomly allocated into three groups: isometric, isotonic, and eccentric exercise groups. All participants will receive a standardized physiotherapy protocol including superficial heat application, transcutaneous electrical nerve stimulation (TENS), and therapeutic ultrasound prior to exercise.

Primary outcomes will include pain intensity assessed by the Visual Analog Scale (VAS) and functional status evaluated using the WOMAC index, 30-second sit-to-stand test, and stair ascent/descent test. Secondary outcomes will include ultrasonographic assessment of muscle architecture, including muscle thickness, fascicle length, pennation angle, and physiological cross-sectional area of the VMO muscle. Additionally, selected hip muscles (adductor group and tensor fascia lata) will be evaluated.

Assessments will be performed at baseline (T0) and after the 8-week intervention (T1) by a blinded assessor. Randomization will be conducted using a computer-generated sequence with allocation concealment.

Statistical analyses will include repeated measures analysis to evaluate within-group and between-group differences, with significance set at p < 0.05.

The findings of this study are expected to contribute to evidence-based rehabilitation by identifying the most effective type of VMO strengthening exercise for improving clinical outcomes and muscle structure in individuals with PFPS.

• Study Type: Interventional
• Enrollment (Estimated): 90
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Muharrem Gökhan Beydağı, PhD; Phone Number: +905323581105; Email: mgbeydagi@firat.edu.tr

Study Locations

• Turkey (Türkiye)
  • MErkez
    • Elâzığ, MErkez, Turkey (Türkiye), 23200
      • Firat University
      • Contact: Muharrem Beydağı, PhD; Phone Number: 05323581105; Email: fztgokhan@hotmail.com
      • Principal Investigator: Muhammet Şahin Elbastı, PhD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Aged between 18 and 40 years
• Clinically diagnosed with patellofemoral pain syndrome
• Presence of anterior knee pain for at least 3 months
• Pain during activities such as stair climbing, squatting, running, or prolonged sitting
• Pain intensity of at least 3/10 on the Visual Analog Scale (VAS)
• Willingness to participate and provide written informed consent

Exclusion Criteria:

• History of knee trauma or surgery
• Meniscal injury, ligament injury, or knee instability
• Advanced osteoarthritis
• Neurological disorders
• Rheumatologic diseases
• Participation in a structured knee rehabilitation program within the last 6 months
• Pregnancy

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Isometric Exercise Group; Participants in this group will receive a standardized physiotherapy program (hot pack, TENS, and therapeutic ultrasound) followed by isometric VMO strengthening exercises performed in the terminal knee extension range (0-30°). Exercises will be performed 3 sets of 10 repetitions, with 10-second contractions, three times per week for 8 weeks.	Other: Isometric VMO Exercise; Isometric contractions of the vastus medialis oblique muscle will be performed with the knee supported at approximately 15° flexion, emphasizing maximal voluntary contraction without joint movement.; Other Names: Experimental: Isometric Exercise Group
Experimental: Isotonic Exercise Group; Participants will receive the same standardized physiotherapy program followed by isotonic (concentric and eccentric) VMO strengthening exercises performed within the 0-30° knee extension range using external resistance. Exercises will be performed 3 sets of 10-15 repetitions, three times per week for 8 weeks.	Other: Isotonic VMO Exercise; Participants will perform controlled concentric and eccentric contractions using ankle weights through a limited range of motion (0-30° knee extension).
Experimental: Eccentric Exercise Group; Participants will receive the same standardized physiotherapy program followed by eccentric VMO strengthening exercises performed within the 0-30° knee extension range. Exercises will be performed 3 sets of 10-15 repetitions, three times per week for 8 weeks.	Other: Eccentric VMO Exercise; Participants will perform eccentric contractions against resistance during knee flexion, with assisted concentric return to the starting position.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
VMO Muscle Architecture (Ultrasound)	Muscle thickness, fascicle length, pennation angle, and physiological cross-sectional area of the vastus medialis oblique muscle will be assessed using ultrasound imaging.	Baseline and Week 8

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Pain Intensity (Visual Analog Scale, VAS)	Pain intensity will be assessed using the Visual Analog Scale (VAS), a 10-cm scale ranging from 0 (no pain) to 10 (worst imaginable pain). Higher scores indicate greater pain intensity.	Baseline and Week 8
Functional Status (WOMAC Index)	Functional status will be evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), including pain, stiffness, and physical function subscales. Higher scores indicate worse functional status.	Baseline and Week 8
30-Second Sit-to-Stand Test	The number of repetitions completed in 30 seconds will be recorded to assess lower extremity functional strength.	Baseline and Week 8
Stair Ascent and Descent Test	Time required to ascend and descend a standardized 9-step staircase will be recorded in seconds.	Baseline and Week 8
Hip Muscle Architecture (Ultrasound)	Muscle architecture parameters of the hip muscles (adductors and tensor fascia lata) will be evaluated using ultrasound imaging.	Baseline and Week 8

Collaborators and Investigators

• Sponsor: Firat University

Study record dates

Study Major Dates

• Study Start (Estimated): May 20, 2026
• Primary Completion (Estimated): June 20, 2026
• Study Completion (Estimated): August 1, 2026

Study Registration Dates

• First Submitted: April 27, 2026
• First Submitted That Met QC Criteria: April 27, 2026
• First Posted (Actual): May 1, 2026

Study Record Updates

• Last Update Posted (Actual): May 12, 2026
• Last Update Submitted That Met QC Criteria: May 7, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Knee Pain; Exercise Therapy; Isometric Exercise; Muscle Architecture; Eccentric Exercise; Vastus Medialis Oblique; Isotonic Exercise
• Additional Relevant MeSH Terms: Musculoskeletal Diseases; Joint Diseases; Patellofemoral Pain Syndrome
• Other Study ID Numbers: FU_MGBeydagi_PFAS_B_2026/05

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No