Effects of Isometric, Isotonic, and Eccentric VMO Exercises in Patellofemoral Pain Syndrome

Official title

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

Overview

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.

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.

Interventions

• 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 Isotonic VMO Exercise
  Participants will perform controlled concentric and eccentric contractions using ankle weights through a limited range of motion (0-30° knee extension).
• Other Eccentric VMO Exercise
  Participants will perform eccentric contractions against resistance during knee flexion, with assisted concentric return to the starting position.

Primary outcome measures

• VMO Muscle Architecture (Ultrasound) [Time frame: Baseline and Week 8]

Secondary outcome measures (5)

• Pain Intensity (Visual Analog Scale, VAS) [Time frame: Baseline and Week 8]
• Functional Status (WOMAC Index) [Time frame: Baseline and Week 8]
• 30-Second Sit-to-Stand Test [Time frame: Baseline and Week 8]
• Stair Ascent and Descent Test [Time frame: Baseline and Week 8]
• Hip Muscle Architecture (Ultrasound) [Time frame: Baseline and Week 8]

Eligibility criteria

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

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) · 1 center

• Firat University — Elâzığ

Identifiers

NCT: NCT07562425 · FU_MGBeydagi_PFAS_B_2026/05

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗