Effect of 0° and 50° N-K Table Load Angles on Quadriceps Activation in Knee Osteoarthritis

Comparative Effectiveness of N-K Table Load Angles at 0° and 50° on Quadriceps Femoris Maximum Voluntary Contraction in Patients With Knee Osteoarthritis

Knee osteoarthritis (OA) is a common degenerative joint disease that leads to pain, reduced mobility, and functional limitation. Quadriceps femoris weakness plays a significant role in disease progression and disability. Isotonic strengthening using the N-K Table allows adjustment of load angles to optimize muscle activation; however, the effect of different load angles on quadriceps activation in patients with knee osteoarthritis remains unclear.

This study aims to compare quadriceps femoris activation at 0° and 50° N-K Table load angles in patients with knee osteoarthritis using surface electromyography (sEMG). A randomized cross-over experimental design is applied to determine whether adjusting the load angle improves maximum voluntary contraction (MVC) during isotonic knee extension exercise.

Study Overview

• Status: Completed
• Conditions: Knee Osteoarthritis; Osteearthritis
• Intervention / Treatment: Other: Isotonic Quadriceps Exercise Using NK Table

Detailed Description

Knee osteoarthritis (OA) is the most prevalent joint disease and a leading cause of disability among older adults. The progressive degeneration of articular cartilage and structural remodeling of the joint result in chronic pain, stiffness, and limited movement. Among the factors contributing to disability, quadriceps femoris weakness plays a central role by impairing knee stability and shock absorption during gait.

Isotonic strengthening exercises using the N-K Table provide a controlled method to restore quadriceps strength while minimizing excessive joint loading. The N-K Table allows adjustment of the load arm angle, which may better align external resistance with the physiological torque profile of the knee extensors, including the vastus medialis, vastus lateralis, and rectus femoris. Although previous studies in healthy adults suggest that higher load angles may optimize torque production, the specific effect in patients with knee osteoarthritis has not been clearly established.

This study employed a randomized cross-over experimental design. A total of 43 female participants aged 50-65 years with unilateral or bilateral knee osteoarthritis (Kellgren-Lawrence grade 2-3) were enrolled. Each participant performed isotonic knee extension exercises at 0° and 50° N-K Table load angles in random order. Exercise intensity was set at 75% of the individual ten-repetition maximum (10RM). Surface electromyography (sEMG) was used to measure maximum voluntary contraction (MVC) of the vastus medialis, vastus lateralis, and rectus femoris. The primary outcome was the difference in MVC between the two load angles. Secondary variables included age, body mass index, and physical activity level.

The study was conducted at the Department of Physical Medicine and Rehabilitation, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia, between January and June 2024. Ethical approval was obtained from the institutional ethics committee, and all participants provided written informed consent prior to participation.

• Study Type: Interventional
• Enrollment (Actual): 43
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Indonesia
  • DKI Jakarta
    • Jakarta, DKI Jakarta, Indonesia, 10430
      • Department of Physical Medicine and Rehabilitation, Dr. Cipto Mangunkusumo General Hospital

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Diagnosed with unilateral or bilateral knee osteoarthritis (OA), grade 2 or 3, in the subacute or chronic phase based on the criteria of the American College of Rheumatology (ACR) and Kellgren-Lawrence classification.
• Female, aged 50-65 years, based on ACR diagnostic criteria.
• Knee flexion-extension range of motion of at least 0-120 degrees.
• Normal cognitive function as assessed using the Montreal Cognitive Assessment Indonesia Version (MoCA-INA) (score ≥26-30)

Exclusion Criteria:

• Knee joint instability due to ligament laxity in the cruciate or collateral ligaments obtained from physical examination (valgus/varus test and anterior/posterior drawer test) or previous supporting examination.
• Presence of deformity in the form of genu varus, genu valgus, or genu recurvatum (Q angle 12-20°).
• History of knee injury (fracture, ligament rupture, or meniscus) or having undergone knee surgery.
• Pain or instability of the ankle joint obtained from physical examination.
• Stroke or disorders of the central and peripheral nervous system.
• Patients with metabolic diseases such as diabetes mellitus and heart disease or other autoimmune diseases based on medical records in unstable condition with pre-prandial capillary blood glucose ≠ 80-130 mg/dL or 1-2 hours post-prandial capillary blood glucose ≠ <180 mg/dL, systolic blood pressure ≠ 90-140 mmHg and diastolic blood pressure ≠ 60-90 mmHg.
• Pain durin loaded knee extension exercise greatetr than 3 on the Visual Analogue Scale (VAS)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: 0° Load Angle NK Table; Participants performed isotonic knee extension exercise using the N-K Table adjusted to a 0° load angle. Exercise intensity was set at 75% of the individual 10-repetition maximum (10RM). Each participant performed controlled knee extension movements from 90° flexion to near full extension. At each load angle, three maximal voluntary contractions were recorded with 3-second rest intervals between trials. Surface electromyography (sEMG) was used to measure maximum voluntary contraction (MVC) of the vastus medialis, vastus lateralis, and rectus femoris muscles.	Other: Isotonic Quadriceps Exercise Using NK Table; Isotonic knee extension exercise performed using the N-K Table device at specified load angles (0° and 50°) with resistance set at 75% of 10RM.
Experimental: 50° Load Angle NK Table; Participants performed isotonic knee extension exercise using the N-K Table adjusted to a 50° load angle. Exercise intensity was set at 75% of the individual 10-repetition maximum (10RM). Each participant performed controlled knee extension movements from 90° flexion to near full extension. At each load angle, three maximal voluntary contractions were recorded with 3-second rest intervals between trials. Surface electromyography (sEMG) was used to measure maximum voluntary contraction (MVC) of the vastus medialis, vastus lateralis, and rectus femoris muscles.	Other: Isotonic Quadriceps Exercise Using NK Table; Isotonic knee extension exercise performed using the N-K Table device at specified load angles (0° and 50°) with resistance set at 75% of 10RM.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximum Voluntary Contraction (MVC) of Quadriceps Femoris Muscles	Maximum voluntary contraction (MVC) of the quadriceps femoris muscles (vastus medialis, rectus femoris, and vastus lateralis) measured using surface electromyography (sEMG) during isotonic knee extension exercise performed on the N-K Table at 0° and 50° load angles. MVC is defined as the highest sEMG amplitude recorded from three maximal voluntary contraction trials for each muscle.	Day 1

Collaborators and Investigators

• Sponsor: Indonesia University

Study record dates

Study Major Dates

• Study Start (Actual): January 20, 2024
• Primary Completion (Actual): June 5, 2024
• Study Completion (Actual): May 25, 2025

Study Registration Dates

• First Submitted: February 25, 2026
• First Submitted That Met QC Criteria: March 4, 2026
• First Posted (Actual): March 6, 2026

Study Record Updates

• Last Update Posted (Actual): March 6, 2026
• Last Update Submitted That Met QC Criteria: March 4, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Knee Osteoarthritis; Surface Electromyography; Quadriceps Femoris; Maximum Voluntary Contraction; Isotonic Muscle Strengthening
• Additional Relevant MeSH Terms: Musculoskeletal Diseases; Arthritis; Joint Diseases; Rheumatic Diseases; Osteoarthritis; Osteoarthritis, Knee
• Other Study ID Numbers: 1207/UN2.F1/ETIK/PPM.0002/2023

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: There is no plan to share individual participant data.

Drug and device information, study documents

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