Effect of Inspiratory Muscle Training on Knee Osteoarthritis Pain

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.