Evaluation of Muscle Oxygenation and Recovery Dynamics in Individuals With Knee Osteoarthritis

Muscle Oxygenation and Recovery Dynamics in Individuals With Knee Osteoarthritis: A Case-Control Study

Knee osteoarthritis (OA) is a degenerative joint disease characterized by pain, muscle weakness, and functional limitations that significantly affect lower limb muscle performance. Structural and physiological alterations in the quadriceps muscle, particularly in the vastus medialis obliquus (VMO), have been reported in individuals with knee OA, including reductions in muscle cross-sectional area, intramuscular fat infiltration, vascular changes, and impaired neuromuscular activation.

Muscle oxygenation (SmO₂) is an objective indicator of the metabolic status and circulatory capacity of skeletal muscle. However, the oxygenation dynamics of the quadriceps muscle before and after exercise in individuals with knee OA have not been sufficiently investigated.

The aim of this study is to evaluate VMO muscle oxygenation at rest, during exercise, and during the recovery period in individuals with knee OA and to compare these parameters with age- and sex-matched healthy individuals. In addition, the study will examine the relationship between muscle oxygenation parameters, muscle strength, functional performance, and pain levels.

Understanding these physiological responses may provide insight into the metabolic mechanisms underlying muscle dysfunction in knee OA and may contribute to the development of more individualized rehabilitation strategies.

Study Overview

• Status: Completed
• Conditions: Healthy Participants; Osteoarthritis of Knee
• Intervention / Treatment: Other: No intervention

Detailed Description

Knee osteoarthritis (OA) is a degenerative joint disorder associated with pain, muscle weakness, and functional limitations that negatively affect lower extremity muscle performance. Previous studies have reported structural and physiological alterations in the quadriceps muscle in individuals with knee OA, particularly in the vastus medialis obliquus (VMO). These alterations include reduced muscle cross-sectional area, increased intramuscular fat infiltration, vascular changes, and impaired neuromuscular activation, which may contribute to decreased knee joint stability and progression of the disease.

Muscle oxygenation (SmO₂) is an important physiological parameter reflecting the balance between oxygen delivery and utilization in skeletal muscle and provides objective information about muscle metabolic and circulatory function. Despite the potential relevance of SmO₂ in understanding quadriceps dysfunction in knee OA, studies investigating exercise-induced oxygenation responses and recovery dynamics in this population remain limited.

This observational, comparative cross-sectional study aims to evaluate VMO SmO₂ dynamics in individuals with knee OA and compare these parameters with healthy controls matched for age and sex. The study will also investigate the associations between SmO₂ parameters, muscle strength, functional performance, and pain intensity.

Individuals diagnosed with knee OA by a physical medicine and rehabilitation physician and healthy volunteers meeting the eligibility criteria will be invited to participate. Written informed consent will be obtained from all participants prior to participation. Participants who meet the inclusion criteria will be allocated into two groups: a knee OA group and a healthy control group. All participants will undergo the same assessment procedures during a single evaluation session.

In accordance with the recommendations of Osteoarthritis Research Society International (OARSI), in participants with bilateral knee OA, the target knee for analysis will be determined using a predefined strategy: (1) the knee with greater pain at rest or during activity will be selected; (2) if pain levels are equal, the knee with greater radiographic severity (Kellgren-Lawrence grade) will be selected; (3) if both pain and radiographic severity are equal, the dominant leg (the extremity preferred for kicking a ball) will be designated as the target knee. The target knee will serve as the reference knee for follow-up measurements, including SmO₂ and knee-specific clinical assessments.

To our knowledge, no previous study has directly compared SmO₂ parameters between individuals with knee OA and healthy controls. Therefore, a study investigating SmO₂ changes in a similar muscle group and using the same measurement technique in individuals who underwent anterior cruciate ligament reconstruction was used as a reference. Sample size estimation was performed using G*Power software (version 3.1) based on a two-tailed independent samples t-test model for comparing the mean difference between two groups. The effect size reported for VMO SmO₂ in the reference study (Cohen's d = 1.02) was used for the calculation. With an alpha level of 0.05, statistical power of 0.80, and a group allocation ratio of 1:1, the required sample size was calculated as 17 participants per group, resulting in a total of 34 participants.

Before the measurements, participants will rest in a seated position for 10 minutes. Pain intensity will be assessed using the Visual Analog Scale (VAS). Following the rest period, SmO₂ measurements will be performed using a near-infrared spectroscopy device (Moxy Monitor) placed over the VMO muscle. Baseline SmO₂ values will be recorded during a 60-second measurement period.

After the baseline measurement, participants will perform a standardized mini-squat exercise task. The mini-squat was selected as a safe and functional closed-chain exercise commonly used in individuals with knee osteoarthritis to activate lower-extremity musculature, and it was combined with isometric hip adduction using a ball placed between the knees to enhance vastus medialis obliquus activation and medial knee stabilization. Immediately following exercise, VMO muscle oxygenation will be monitored, and the recovery process will be recorded. Recovery time will be defined as the duration required for the SmO₂ value to return to its baseline level while the participant rests in a seated position.

After completion of the recovery measurements, participants will rest for 10 minutes to minimize the effects of fatigue. Subsequently, muscle strength will be assessed using an isokinetic dynamometer through maximal voluntary isometric knee extension contractions performed at 15° of knee flexion. This joint angle was selected because the vastus medialis obliquus demonstrates greater activation near terminal knee extension. Additionally, testing at 15° places the quadriceps in a biomechanically advantageous position for torque production while minimizing joint stress. Participants will perform three maximal contractions, each lasting approximately 6 seconds, with standardized verbal encouragement and 60-second rest intervals; the mean peak torque value will be used for analysis. Functional performance will then be assessed using the 30-Second Sit-to-Stand Test. All measurements will be performed during a single session, and participants will not be followed longitudinally.

Statistical analyses will be performed using SPSS. Data distribution will be assessed using normality tests. Descriptive statistics will be presented as mean ± standard deviation or median as appropriate. Group differences between individuals with knee OA and healthy controls will be analyzed using independent samples t-test or Mann-Whitney U test. Associations between muscle oxygenation parameters, muscle strength, functional performance, and pain will be examined using Pearson or Spearman correlation analyses. A p-value < 0.05 will be considered statistically significant.

• Study Type: Observational
• Enrollment (Actual): 34

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Büyükçekmece
    • Istanbul, Büyükçekmece, Turkey (Türkiye), 34000
      • Istanbul University-Cerrahpaşa, Faculty of Health Sciences, Physiotherapy and Rehabilitation Lab.

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

The study population will consist of adults aged 45-65 years, including individuals diagnosed with knee osteoarthritis (Kellgren-Lawrence grade 2-3) according to the American College of Rheumatology criteria and age- and sex-matched healthy controls. All participants will meet the predefined eligibility criteria and provide written informed consent prior to participation.

Description

Inclusion Criteria:

• Age between 45 and 65 years
• Body mass index (BMI) below 30 kg/m²
• Willingness to participate in the study

Additional criteria for the knee osteoarthritis group:

• Diagnosis of knee osteoarthritis confirmed by a physician according to the American College of Rheumatology diagnostic criteria
• Bilateral knee osteoarthritis classified as Kellgren-Lawrence grade 2 or 3

Exclusion Criteria:

• Presence of another orthopedic or rheumatologic condition affecting the lower extremity
• Uncontrolled hypertension
• Presence of lower extremity arterial or venous disorders
• Presence of a neurological disease
• Cognitive, learning, or perception impairments
• Knee extension deficit
• Physical activity level exceeding 600 MET-min/week according to the International Physical Activity Questionnaire Short Form (IPAQ-SF)
• Participation in a physiotherapy and rehabilitation program for knee osteoarthritis within the last 6 months
• Intra-articular knee injection within the past 6 months

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Knee Osteoarthritis; Participants diagnosed with bilateral knee osteoarthritis according to the American College of Rheumatology criteria and classified as Kellgren-Lawrence grade 2-3.	Other: No intervention; 15-repetition mini-squat exercise is used only as an assessment task.
Healthy Controles; Age- and sex-matched healthy individuals without knee osteoarthritis or lower extremity musculoskeletal disorders.	Other: No intervention; 15-repetition mini-squat exercise is used only as an assessment task.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Muscle Oxygenation	Muscle oxygenation (SmO₂) of the vastus medialis obliquus will be measured using near-infrared spectroscopy (Moxy Monitor, Fortiori Design LLC, USA). SmO₂ values will be recorded at rest (baseline), immediately after the mini-squat exercise, and throughout the recovery period. The primary outcome will include the magnitude of SmO₂ change following exercise and the recovery time required for SmO₂ to return to its baseline value.	Measured during the single assessment session

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximal Isometric Quadriceps Strength	Maximal voluntary isometric quadriceps torque measured using an isokinetic dynamometer (Biodex System). Participants will perform three maximal isometric knee extension contractions at 15° knee flexion, each lasting approximately 6 seconds. The mean peak torque (Nm) will be used for analysis.	Measured during the single assessment session
Functional Performance - 30-Second Sit-to-Stand Test	Functional performance will be assessed using the 30-second sit-to-stand test. The number of complete stands performed within 30 seconds will be recorded.	Measured during the single assessment session
Pain Intensity	Pain intensity will be assessed using the Visual Analog Scale (VAS), a 10-cm scale ranging from "no pain" to "worst imaginable pain."	Measured before the assessment session

Collaborators and Investigators

• Sponsor: Bahçeşehir University
• Collaborators: Istanbul Aydın University; Istanbul University - Cerrahpasa
• Investigators: Principal Investigator: Ayşem Ecem Özdemir, PT, Msc, Bahcesehir university; Study Chair: Yıldız Analay Akbaba, PT, PhD, Istanbul University - Cerrahpasa; Study Chair: Gökhan Özkoçak, MD, PhD, Istanbul Aydın University

Publications and helpful links

General Publications

• Alghadir AH, Anwer S, Iqbal A, Iqbal ZA. Test-retest reliability, validity, and minimum detectable change of visual analog, numerical rating, and verbal rating scales for measurement of osteoarthritic knee pain. J Pain Res. 2018 Apr 26;11:851-856. doi: 10.2147/JPR.S158847. eCollection 2018.
• Hunter DJ, Bierma-Zeinstra S. Osteoarthritis. Lancet. 2019 Apr 27;393(10182):1745-1759. doi: 10.1016/S0140-6736(19)30417-9.
• Earl JE, Schmitz RJ, Arnold BL. Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction. J Electromyogr Kinesiol. 2001 Dec;11(6):381-6. doi: 10.1016/s1050-6411(01)00024-4.
• Crum EM, O'Connor WJ, Van Loo L, Valckx M, Stannard SR. Validity and reliability of the Moxy oxygen monitor during incremental cycling exercise. Eur J Sport Sci. 2017 Sep;17(8):1037-1043. doi: 10.1080/17461391.2017.1330899. Epub 2017 May 30.
• Feldmann A, Schmitz R, Erlacher D. Near-infrared spectroscopy-derived muscle oxygen saturation on a 0% to 100% scale: reliability and validity of the Moxy Monitor. J Biomed Opt. 2019 Nov;24(11):1-11. doi: 10.1117/1.JBO.24.11.115001.
• Carpenter MR, Carpenter RL, Peel J, Zukley LM, Angelopoulou KM, Fischer I, Angelopoulos TJ, Rippe JM. The reliability of isokinetic and isometric leg strength measures among individuals with symptoms of mild osteoarthritis. J Sports Med Phys Fitness. 2006 Dec;46(4):585-9.
• Daşkapan, A., KÜLÜNKOĞLU, B., Özünlü Pekyavaş, N., Tüzün, E., Nur Coşar, S., & Karataş, M.; Comparison of mini-squats and straight leg raises in patients with knee osteoarthritis: A randomized controlled clinical trial; Turkish Journal of Rheumatology; 2013; 28(1); 016-026.
• Edwards MH, van der Pas S, Denkinger MD, Parsons C, Jameson KA, Schaap L, Zambon S, Castell MV, Herbolsheimer F, Nasell H, Sanchez-Martinez M, Otero A, Nikolaus T, van Schoor NM, Pedersen NL, Maggi S, Deeg DJ, Cooper C, Dennison E. Relationships between physical performance and knee and hip osteoarthritis: findings from the European Project on Osteoarthritis (EPOSA). Age Ageing. 2014 Nov;43(6):806-13. doi: 10.1093/ageing/afu068. Epub 2014 Jun 10.
• Jun, I., Lee, Y., Shin, C.; The effects of isometric extension at different knee angles on vastus medialis electromyographic activity in patients with knee joint osteoarthritis; Journal of Physical Therapy Science; 2012; 24 (9), 855-857.
• Taniguchi M, Fukumoto Y, Yagi M, Hirono T, Yamagata M, Asayama A, Okada S, Nakai R, Kobayashi M, Ichihashi N. A higher intramuscular fat in vastus medialis is associated with functional disabilities and symptoms in early stage of knee osteoarthritis: a case-control study. Arthritis Res Ther. 2023 Apr 14;25(1):61. doi: 10.1186/s13075-023-03048-0.
• Noehren B, Kosmac K, Walton RG, Murach KA, Lyles MF, Loeser RF, Peterson CA, Messier SP. Alterations in quadriceps muscle cellular and molecular properties in adults with moderate knee osteoarthritis. Osteoarthritis Cartilage. 2018 Oct;26(10):1359-1368. doi: 10.1016/j.joca.2018.05.011. Epub 2018 May 23.

Helpful Links

• The Moxy sensor will be placed at the midpoint of the vastus medialis obliquus muscle, based on anatomical reference points according to SENIAM guidelines.

Study record dates

Study Major Dates

• Study Start (Actual): March 1, 2026
• Primary Completion (Actual): June 5, 2026
• Study Completion (Actual): June 5, 2026

Study Registration Dates

• First Submitted: March 10, 2026
• First Submitted That Met QC Criteria: March 10, 2026
• First Posted (Actual): March 13, 2026

Study Record Updates

• Last Update Posted (Actual): June 15, 2026
• Last Update Submitted That Met QC Criteria: June 12, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Pain; Muscle Strength; Osteoarthritis of Knee; Muscle oxygenation
• Additional Relevant MeSH Terms: Neurologic Manifestations; Musculoskeletal Diseases; Arthritis; Joint Diseases; Rheumatic Diseases; Osteoarthritis; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Pain; Osteoarthritis, Knee
• Other Study ID Numbers: MONO1

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