Respiratory Muscle Strength, Endurance, and Postural Control in Chronic Neck Pain With Disability

Lung function will be measured with a portable spirometer. The test will record forced vital capacity, the amount of air exhaled in one second, their ratio, and peak flow. Results will be given in liters and compared to predicted normal values. The test follows official guidelines and uses sterilized, personal mouthpieces to ensure safety.

Maximum inspiratory mouth pressure is the intraoral pressure measured during maximum inspiration against a closed airway valve. For the measurement, the participant is asked to perform a maximum expiration first. Then, the airway valve is closed, and the participant performs a maximum inspiration, maintaining it for 1-3 seconds. The best value out of three attempts will be selected and recorded in cmH₂O. Results will be expressed as a percentage of normal reference values calculated according to age and gender.

Cervical disability will be evaluated using the Turkish version of the Neck Disability Questionnaire. This is one of the most commonly used questionnaires for neck pain. It is used to assess the patient's current condition and progress during treatment. The questionnaire consists of 10 sections completed by the patient, covering pain, personal care, lifting heavy objects, reading, headaches, concentration, work, driving, sleeping, and recreation. Each section is scored from 0 (no disability) to 5 (complete disability). The total score ranges from 0 (no disability) to 50 (total disability). An increase in the score indicates greater disability, while a decrease indicates improvement. Based on the total score, disability is classified as follows: 0-4 points (0-8%) no disability, 5-14 points (10-28%) mild disability, 15-24 points (30-48%) moderate disability, 25-34 points (50-64%) severe disability, and 35-40 points (70-100%) complete disability (Vernon et al., 1991; Telci et al., 2009).

Respiratory muscle endurance refers to the ability of the respiratory muscles to sustain performance during prolonged or repetitive contractions. This parameter is typically assessed with specific endurance tests and may vary depending on the measurement protocol. During the endurance test, the participant sustains respiratory muscle activity under a given load or intensity for a specified duration, and performance values are recorded.

Maximum Expiratory Pressure is the intraoral pressure measured during maximum expiration against a closed airway valve. For the measurement, the participant first performs a maximum inspiration. Then, the airway valve is closed, and the participant performs maximum expiration, maintaining it for 1-3 seconds. The highest value out of three attempts will be selected and recorded in cmH₂O. Results will be expressed as a percentage of normal reference values calculated according to age and gender.

Waist circumference and chest circumference measurements at three different regions will be taken.

For postural analysis, the form developed by Corbin et al. will be used. Scoring will be performed according to the severity of postural deviations observed from the lateral and posterior views (Corbin et al., 2006).

Perceived exertion, fatigue, and breathlessness will be assessed using the Visual Analog Scale (VAS) ranging from 0 (none) to 10 (very severe).

The Functional Reach Test will assess postural control using a tape fixed to a wall. Participants stand close to the wall and reach forward with their dominant arm without stepping or lifting heels. Three trials will be done, averaging the last two. Before testing, handedness will be determined. Modified tests include reaching with both arms and on soft surfaces, as well as reaching sideways.

Perceived exertion, fatigue, and breathlessness will be assessed using modified Borg scale, ranging from 0 (none) to 10 (very severe).