Effect of Resistance Training in Water with Blood Flow Restriction on Heart Rate Variability, Functional Capacity, and Pain in Postmenopausal Women with Knee Osteoarthritis

Background: Resistance training has been suggested as a potential treatment for knee osteoarthritis but may be harmful to people with chronic pain. The fear of this pain and chronic inflammation leads to disorder in the automatic nervous system and reduces activity, heart rate variability, and cardiovascular fitness. This study aimed to investigate the effect of a combination of aquatic resistance training and blood flow restriction on heart rate variability, functional capacity, and pain in postmenopausal women with knee osteoarthritis. Methods: Thirty-eight postmenopausal women with grade 2 and 3 arthritis were randomly assigned to three groups by drawing lots: water resistance training (AQE, n=13), water resistance training with BFR (BFR+AQE, n=14), and control group (n=11). One week before the beginning and 48 hours after the last session of the intervention program, heart rate variability, functional capacity, and subjects’ pain were evaluated. RMSSD, SDNN, LF, and HF were measured at rest and while walking to evaluate heart rate variability. Functional capacity was measured by assessing functions, including standing on a chair, getting up and walking, walking speed, two minutes of walking, and dynamic balance. The study’s protocol was also registered in the Iranian Registry of Clinical Trials (registration No.: IRCT20240911063005N1). Results: According to the results, after the intervention period, there was a significant increase in the HFpeak index (P=0.049) and a significant increase in the low-frequency/high-frequency walking ratio (P=0.015) in the AQE group, a decrease in standing time on a chair (improvement) in both exercise groups (P=0.002), a significant increase in the dynamic balance in the AQE BFR exercise group (P=0.004), and a significant decrease in the pain index in the AQE exercise group (P=0.009). No significant difference was observed between the exercise groups in the other measured indicators. Conclusion: Our results suggest that resistance training reduces stress, inflammation, and pain caused by physical problems through increased parasympathetic and vagal activity. Increased heart rate variability indicates cardiovascular flexibility, adaptation to exercise, and improved mental health (e.g., reduced anxiety and pain). This, in turn, increases mobility and physical activity in these individuals and can prevent the onset or development of disease by increasing HF and the LF/HFw ratio. Combining aquatic resistance training and BFR is an innovative and practical approach to improving the quality of life of people with knee osteoarthritis. Also, improvement in HRV after non-pharmacological interventions (e.g., resistance exercise, aerobics, tai chi, meditation) can indicate the effectiveness of treatment. This helps clinicians adopt more personalized approaches.