Effect of Inspiratory Muscle Training on Knee Osteoarthritis Pain

Effect of Inspiratory Muscle Training on Pain in Patients With Knee Osteoarthritis: A Randomized Controlled Trial

Knee osteoarthritis (KOA) is a common joint disease that causes chronic pain and limits daily activities. Current treatments, such as painkillers or surgery, have limitations like side effects or high costs. This study will test whether a safe, non-drug intervention-inspiratory muscle training (breathing exercises against resistance)-can reduce knee pain in people with KOA. The training may work by lowering inflammation and improving the body's nervous system control of pain.

We plan to enroll 80 patients aged ≥55 years with confirmed KOA and frequent knee pain. Participants will be randomly assigned to either an 8-week inspiratory muscle training program (5 sessions per week, with gradually increasing resistance) or a sham (very low resistance) training program. Neither the patients nor the researchers assessing the outcomes will know who is in which group.

The main outcome is change in knee pain measured by a visual analog scale (VAS). Secondary outcomes include blood markers of inflammation (TNF-α, IL-6, IL1β), physical function, WOMAC score (a KOA-specific questionnaire), activity level, sleep quality, and quality of life. To explore underlying mechanisms, we will also measure heart rate variability (HRV) as an indicator of autonomic nervous system function, and brain functional connectivity in the prefrontal cortex using functional near-infrared spectroscopy (fNIRS). These mechanistic assessments will be performed at baseline and at the end of 8-week intervention. Additional follow-up assessments for clinical outcomes will be done at 3 and 6 months after the training ends. We will also record any side effects or adverse events.

This study will provide high-quality evidence on whether inspiratory muscle training is an effective and safe complementary treatment for knee pain in people with knee OA, and will offer new insights into the mechanisms underlying its analgesic effects.

Study Overview

• Status: Not yet recruiting
• Conditions: Knee Osteoarthritis; Knee Osteoarthritis (Knee OA)
• Intervention / Treatment: Other: Inspiratory muscle training

• Study Type: Interventional
• Enrollment (Estimated): 80
• Phase: Not Applicable

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Aged 55 years or older.
• Knee osteoarthritis (Kellgren-Lawrence grade ≥ 2).
• Knee pain (Visual Analogue Scale, VAS ≥ 3) on the most days in the past month.
• Able to walk independently without assitive devices.

Exclusion Criteria:

• History of knee replacement surgery, meniscus surgery, or ligament surgery.
• Received corticosteroid injection within the previous three weeks.
• Diagnosed with rheumatoid arthritis.
• Unstable angina, recent myocardial infarction, uncontrolled cardiac arrhythmia, or severe heart failure.
• History of stroke.
• Currently receiving steroid therapy, hormonal therapy, or cancer chemotherapy.
• Pneumothorax, pulmonary bullae, lung surgery within the past 12 months, unstable asthma, or severe dyspnea at rest.
• Unable to understand the study procedures and potential risks.

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Inspiratory Muscle Training; 5 sessions/week for 8 weeks. Load starts at 50% MIP for 40 reps, increases to 80% MIP for 60 reps from week 5, then adjusted weekly to 80% of updated MIP. Device: threshold inspiratory muscle trainer.	Other: Inspiratory muscle training; Participants will perform home-based inspiratory muscle training using a threshold-loading device (POWERbreathe Medic Plus). Training is conducted 5 times per week for 8 weeks. The initial inspiratory load is set at 50% of the individual's maximum inspiratory pressure (MIP), measured weekly at the study site. The load is progressively increased to 80% MIP over the first 4 weeks and maintained at 80% MIP for the remaining 4 weeks. Each session consists of 40-60 breaths. Adherence is monitored via an electronic training log and weekly on-site visits. This protocol is individualized, progressive, and home-based, distinguishing it from fixed-load or supervised-only breathing interventions.; Other Names: Respiratory muscle training
Sham Comparator: Sham Inspiratory Muscle Training; Participants perform sham inspiratory muscle training with the same frequency and duration as the experimental group, but the inspiratory load is fixed at 10% of maximal inspiratory pressure (MIP) and does not progress. All other procedures (weekly MIP measurement for sham load adjustment) are identical to maintain blinding.	Other: Inspiratory muscle training; Participants will perform home-based inspiratory muscle training using a threshold-loading device (POWERbreathe Medic Plus). Training is conducted 5 times per week for 8 weeks. The initial inspiratory load is set at 50% of the individual's maximum inspiratory pressure (MIP), measured weekly at the study site. The load is progressively increased to 80% MIP over the first 4 weeks and maintained at 80% MIP for the remaining 4 weeks. Each session consists of 40-60 breaths. Adherence is monitored via an electronic training log and weekly on-site visits. This protocol is individualized, progressive, and home-based, distinguishing it from fixed-load or supervised-only breathing interventions.; Other Names: Respiratory muscle training

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Visual analogue scale	Self-rated pain intensity of knee (0-10), "0" indicate no pain, "10" indicate worst pain.	Baseline, week 8, 3-month after intervention, 6-month after intervention

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Western Ontario and McMaster Universities Osteoarthritis Index	Patient-reported outcomes in symptoms and function, total scores range from 0-96, the higher scores indicating the worse symptom and function.	Baseline, week 8, 3-month after intervention, 6-month after intervention
Serum levels of inflammatory markers	Systemic inflammation	Baseline, up to week 8
Heart rate variability	Vagus nerve activity	Baseline, up to week 8
Prefrontal cortex activity	Functional near-infrared spectroscopy was used to assess prefrontal cortex activity	Baseline, up to week 8
40-meter walk test	Physical function	Baseline, up to week 8
30-sec chair stand test	Physical function	Baseline, up to week 8
Physical Activity Scales for the Elderly	Total scores range from 0-793, the higher scores indicating a higher level of physical activity.	Baseline, week 8, 3-month after intervention, 6-month after intervention
Pittsburgh Sleep Quality Index	Total scores range from 0-21, '0' indicating no difficulty and '21' indicating severe difficulties in all areas.	Baseline, week 8, 3-month after intervention, 6-month after intervention
12-Item Short Form Health Survey	Total scores range from 0-100, the higher scores indicating better physical and mental health functioning.	Baseline, week 8, 3-month after intervention, 6-month after intervention
Maximal inspiratory pressure	Inspiratory muscle strength	Baseline, up to week 8

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Adherence	Adherence was calculated from logbooks as completed versus prescribed sessions	Up to week 8
Adverse events	Adverse events were defined as any symptom or abnormal sign during training and graded by the Common Terminology Criteria for Adverse Events (CTCAE v6.0, 2025): Mild: resolved with rest, no medical intervention; Moderate: require minimal medical intervention (e.g., analgesics); Severe: requires medical attention or hospitalization (e.g., clinic visit)	Up to week 8

Collaborators and Investigators

• Sponsor: The Hong Kong Polytechnic University

Study record dates

Study Major Dates

• Study Start (Estimated): July 1, 2026
• Primary Completion (Estimated): July 1, 2030
• Study Completion (Estimated): July 1, 2030

Study Registration Dates

• First Submitted: July 7, 2026
• First Submitted That Met QC Criteria: July 7, 2026
• First Posted (Actual): July 13, 2026

Study Record Updates

• Last Update Posted (Actual): July 13, 2026
• Last Update Submitted That Met QC Criteria: July 7, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: Chronic Pain; Knee Osteoarthritis; Inspiratory Muscle Training
• Additional Relevant MeSH Terms: Pain; Neurologic Manifestations; Musculoskeletal Diseases; Arthritis; Joint Diseases; Rheumatic Diseases; Osteoarthritis; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Osteoarthritis, Knee; Chronic Pain; Therapeutics; Mind-Body Therapies; Complementary Therapies; Exercise Movement Techniques; Physical Therapy Modalities; Breathing Exercises
• Other Study ID Numbers: ZHSC-1-(2026)014

Drug and device information, study documents

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