Effect of Inspiratory Muscle Training on Knee Osteoarthritis Pain

NCT07698418 — Not applicable, Not yet recruiting, 80 participants, The Hong Kong Polytechnic University

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

Registry	NCT07698418
Status	Not yet recruiting
Phase	Not applicable
Study type	Interventional; randomized, parallel, masking: triple, treatment
Enrollment	80 (Estimated)
Sponsor	The Hong Kong Polytechnic University (Other); collaborators: Zunyi Medical College
Conditions	Knee Osteoarthritis, Knee Osteoarthritis (Knee OA)
Interventions	Inspiratory muscle training, Sham inspiratory muscle training (Other)
Dates	start 2026-09-01 (estimated), primary completion 2030-09-01 (estimated), completion 2030-09-01 (estimated), first posted 2026-07-13, last updated 2026-07-16

-Summary

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 brain's modulation of pain.

Eighty patients aged ≥55 years with confirmed KOA and frequent knee pain will be enrolled. 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, the Knee injury and Osteoarthritis Outcome Score (KOOS), inspiratory muscle strength, activity level, sleep quality, and quality of life. To explore underlying mechanisms, outcomes included 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) are collected. 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. Any side effects or adverse events will be recorded.

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.

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+Arms and interventions

Arm	Type	Interventions	Description
Inspiratory Muscle Training	Experimental	Other: 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.
Sham Inspiratory Muscle Training	Sham comparator	Other: 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.

Inspiratory muscle training (Other), also known as Respiratory 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.
Sham inspiratory muscle training (Other): 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 10% of the individual's maximum inspiratory pressure (MIP), measured weekly at the study site. The load is maintained 10% MIP over 8 weeks. Each session consists of 40-60 breaths. Adherence is monitored via an electronic training log and weekly on-site visits.

+Outcome measures

Primary outcomes

Visual analogue scale [Baseline, week 8, 3-month after intervention, 6-month after intervention]: Self-rated pain intensity of knee (0-100), "0" indicate no pain, "100" indicate worst pain.

Secondary outcomes

The Knee injury and Osteoarthritis Outcome Score [Baseline, week 8, 3-month after intervention, 6-month after intervention]: Patient-reported outcomes in pain, symptoms, daily living activities, sports and recreational activities, and quality of life, with the score of each subscale ranging from 0-100, where higher scores indicate worse conditions.
Serum levels of inflammatory markers [Baseline, up to week 8]: Systemic inflammation
Heart rate variability [Baseline, up to week 8]: Vagus nerve activity
Prefrontal cortex activity [Baseline, up to week 8]: Functional near-infrared spectroscopy is used to assess prefrontal cortex activity
40-meter walk test [Baseline, up to week 8]: Physical function
30-sec chair stand test [Baseline, up to week 8]: Physical function
Physical Activity Scales for the Elderly [Baseline, week 8, 3-month after intervention, 6-month after intervention]: Total scores range from 0-793, where the higher scores indicate a higher level of physical activity.
Pittsburgh Sleep Quality Index [Baseline, week 8, 3-month after intervention, 6-month after intervention]: Total scores range from 0-21, '0' indicating no difficulty and '21' indicating severe difficulties in all areas.
12-Item Short Form Health Survey [Baseline, week 8, 3-month after intervention, 6-month after intervention]: Total scores range from 0-100, where the higher scores indicate better physical and mental health function.
Maximal inspiratory pressure [Baseline, up to week 8]: Inspiratory muscle strength

Other outcomes

Adherence [Up to week 8]: Adherence is calculated from logbooks as completed versus prescribed sessions
Adverse events [Up to week 8]: Adverse events are 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)

+Eligibility

Sex: All, ages: 55 Years to 80 Years

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.

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