Postural Biofeedback and Exercise in Axial Spondyloarthritis

• Standard Exercise Program (Behavioral): Participants in both study groups will receive a standard exercise program for 8 weeks, with two physiotherapist-supervised sessions per week and approximately 45 minutes per session. The program will include warm-up, spinal mobility exercises, stretching exercises, postural exercises, trunk stabilization exercises, lower extremity strengthening exercises, breathing exercises, and cool-down. Exercises will be performed at moderate intensity according to the participant's clinical condition and exercise tolerance. Set number, repetitions, and resistance will be progressively increased by the physiotherapist according to individual performance.
• Wearable Postural Biofeedback (Behavioral): Participants in the intervention group will additionally use a wearable postural biofeedback device (Kodgem Straight™, Türkiye) for 8 weeks. The device uses inertial sensors to monitor the position of the upper thoracic region in real time and provides vibrotactile feedback when a predefined postural threshold is exceeded. The device will be individually calibrated before use. Participants will be instructed to use the device three days per week for at least 3 hours per day during activities requiring prolonged static posture, such as desk work, computer use, meal preparation, or ironing. Device adherence will be monitored and recorded by the researcher.

Primary outcomes

• Change in Disease Activity Assessed by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) [Baseline to Week 8]: Disease activity will be assessed using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). The BASDAI consists of 6 items assessing fatigue, axial pain, peripheral joint pain or swelling, localized tenderness, and the severity and duration of morning stiffness. Each item is scored from 0 to 10, with higher scores indicating greater disease activity.

Secondary outcomes

• Change in Axial Pain Intensity Assessed by the Numeric Rating Scale (NRS) [Baseline to Week 8]: Axial/spinal pain intensity will be assessed using an 11-point Numeric Rating Scale ranging from 0 (no pain) to 10 (worst pain imaginable).
• Change in Functional Status Assessed by the Bath Ankylosing Spondylitis Functional Index (BASFI) [Baseline to Week 8]: Functional limitations in daily activities will be assessed using the 10-item BASFI. Scores range from 0 to 10, with higher scores indicating greater functional limitation.
• Change in Spinal Mobility Assessed by the Bath Ankylosing Spondylitis Metrology Index (BASMI) [Baseline to Week 8]: Spinal mobility will be assessed using the BASMI, which includes tragus-to-wall distance, modified Schober test, lumbar lateral flexion, intermalleolar distance, and cervical rotation. Higher scores indicate greater limitation in spinal mobility.
• Change in Health-Related Quality of Life Assessed by the Ankylosing Spondylitis Quality of Life Scale (ASQoL) [Baseline to Week 8]: Disease-specific health-related quality of life will be assessed using the 18-item ASQoL. Scores range from 0 to 18, with higher scores indicating poorer quality of life.
• Change in Postural Alignment Assessed by the New York Posture Assessment Method [Baseline to Week 8]: Postural alignment will be assessed observationally in the frontal and sagittal planes, including the head, shoulders, spine, pelvis, hips, knees, and ankles. Higher total scores indicate better postural alignment.
• Change in Functional Exercise Capacity Assessed by the Two-Minute Walk Test [Baseline to Week 8]: Functional exercise capacity will be assessed by the total distance walked in meters during a 2-minute walk test on a 30-meter walking course. A greater walking distance indicates better functional exercise capacity.
• Global Perceived Change Assessed by the Global Rating of Change Scale (GROC) [Week 8]: Participants' perceived overall improvement will be assessed using the Global Rating of Change Scale, ranging from -7 (very much worse) to +7 (very much better).
• Perceived Usability of the Wearable Postural Biofeedback Device Assessed by the System Usability Scale (SUS) [Week 8]: Perceived usability of the wearable postural biofeedback device will be assessed using the 10-item System Usability Scale. The SUS is scored on a 0-100 scale, with higher scores indicating better perceived usability.

Sex: All, ages: 18 Years to 65 Years

Inclusion Criteria:

* Be between 18 and 65 years of age.
* Have a diagnosis of ankylosing spondylitis or axial spondyloarthritis according to the modified New York or ASAS classification criteria.
* Have had stable medical treatment with no changes in medication during the previous 3 months.
* Have axial/spinal pain intensity of at least 4 out of 10 on the Numeric Pain Rating Scale during the previous week.
* Be able to walk independently.
* Voluntarily agree to participate in the study and provide written informed consent.

Exclusion Criteria:

* History of spinal surgery within the previous 6 months.
* Any change in medical treatment, including biological agents or analgesic treatment, within the previous 3 months.
* Presence of fibromyalgia or another secondary chronic pain syndrome that may substantially affect pain perception.
* Serious cardiopulmonary, neurological, or orthopedic conditions that prevent participation in exercise.
* Pregnancy.
* Dermatological or allergic skin reactions or other skin conditions that prevent the use of the wearable device.
* Regular participation in a structured exercise or rehabilitation program supervised by a physiotherapist for axial spondyloarthritis within the previous 3 months.

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