Binaural Beats Stimulation on the Autonomic Nervous System (ANS), Kinesiophobia and Fitness Levels in Professional Athletes With Musculoskeletal (MSK) Injuries

Sympathetic Skin Response (SSR) test will be used to assess the changes of the Autonomic Nervous System (ANS). SSR will be assessed by calculating the latency and the amplitude. The Latency was measured from the onset of the stimulus artefact to the first deflection from baseline (in seconds) and amplitude was measured peak-to-peak (from negative to positive peak, in millivolts). The Sympathetic Skin Response will be carried out using Electromyography (EMG). Electrical stimuli were delivered to the right wrist at an intensity of 75 mA and a duration of 0.1 ms. The band-pass filter was set between 0.5 and 2000 Hz. Five stimuli were administered unpredictably at random intervals of at least 30 seconds. The shortest latency and the highest amplitude response values among the five responses were used for statistical analysis. Parameters included in the analysis were: SSR upper limb latency, SSR upper limb amplitude, SSR lower limb latency, and SSR lower limb amplitude.

Tampa Scale of Kinesiophobia questionnaire (TSK-17) will be used translated to Greek. It has been tested for its reliability and validity. Scale from 17 to 68. 17 means the person experiences low level of kinesiophobia and 68 means the person experiences high level of kinesiophobia.

An incremental exercise test will be used to assess the aerobic capacity. This method is commonly used to evaluate maximal oxygen uptake (VO₂max) and involves a protocol of progressively increasing exercise intensity until volitional exhaustion. Participants will run on a motorized treadmill set at a constant incline of 0%. Running speed will begin at approximately 8-9 km/h and will increase by 1 km/h at the end of each 1-minute stage. Respiratory variables will be continuously measured on a breath-by-breath basis using a gas analysis system. The test will be terminated when participants reach volitional exhaustion, when oxygen uptake values plateau or decrease despite further increases in workload and ventilation or when the respiratory exchange ratio exceeds 1.10. Total test duration is expected to be approximately 8-12 minutes.

Heart Rate Variability (HRV) is a tool to assess the Autonomic Nervous System function. HRV will be recorded using a telemetric heart rate monitor (Polar H10). Recordings will be conducted in a quiet, calm room, with participants in the supine position. Participants will be instructed not to move, talk, and to breathe normally while remaining supine during the recording. All participants will perform an incremental exercise test on a treadmill at a constant 0% incline, with intensity gradually increasing every minute. Prior to the test, participants will lie supine for 5 minutes while resting HRV is recorded. Participants will then follow the exercise protocol and at the end of the exercise, they will be asked to remain supine for 15 minutes. The time required for HRV to return to each participant's resting level will be recorded. The test will be automatically terminated once participants reach 85% of their maximum heart rate (HRmax) or voluntarily.

Sport competition anxiety questionnaire (SCAT) will be used translated to Greek. It has been tested for its reliability and validity. Scale from 10 to 30. Scores under 17 show low level of competition anxiety. Scores over 24 show high level of competition anxiety.

Pain Beliefs and Perceptions Inventory questionnaire (PBPI-16) will be used translated to Greek. It has been tested for its reliability and validity. Scale from -32 to 32. -32 means the person does not express negative beliefs, 32 means the person expresses negative beliefs.

The Hand Grip Strength Test will be used to assess grip strength through the performance of a maximal voluntary contraction. A portable Kinvent hand dynamometer will be used for the assessment. The test will be performed in a seated position with the shoulder in a neutral position, the elbow flexed at 90° without support, the forearm in a neutral position, and the wrist positioned between 0° and 30° of dorsiflexion and 0°-15° of ulnar deviation. Participants will perform three maximal efforts, each lasting 30 seconds, with a 1-minute rest period between attempts. The test will be conducted in the same manner for both upper limbs. For statistical analysis, the mean value of the three trials will be calculated separately for each upper limb.

Blood lactate concentration will be measured before the incremental exercise test and at the end of the test.