Relaxation Methods in Athletes and Non-Exercising Individuals – Effects on Reaction Time, Coordination, and Body Composition

Participants will be randomly allocated to one of four intervention arms using a computer-generated randomisation procedure. Allocation concealment will be ensured using sealed opaque envelopes prepared by a researcher not involved in outcome assessment. This study does not use a crossover design; therefore, no washout period is applicable. All interventions will be delivered face-to-face in the university research laboratory by a licensed physiotherapist to ensure procedural consistency and participant safety. Each intervention will be performed three times per week over a 12-week period. Adherence will be quantified as the percentage of completed sessions relative to the total planned sessions. Attendance will be verified by the supervising physiotherapist using structured session checklists. Intervention fidelity will be ensured through standardized written protocols and regular supervision meetings within the research team. All interventions will follow standardized protocols; however, minor adjustments (e.g., limb positioning or stretch range) may be made to accommodate individual anthropometric characteristics while maintaining procedural consistency. The percussive massage intervention will target predefined muscles of the dominant lower limb associated with neuromuscular reaction performance, force production, and postural control. The treated muscles will include the quadriceps femoris (vastus lateralis and vastus medialis), biceps femoris, and the medial head of the gastrocnemius. Muscle selection is based on their primary involvement in knee extension and flexion, ankle plantarflexion, and their contribution to rapid neuromuscular activation. Neuromuscular reaction time will be defined as the primary outcome and objectively quantified using surface electromyography (sEMG). Reaction time will be operationally defined as the latency between the presentation of an external stimulus and the onset of muscle activation recorded by sEMG. Postural control will be assessed as a secondary outcome through centre of pressure (COP) analysis obtained from force platform measurements. Percussive massage will be delivered using a calibrated handheld percussive therapy device with a standardized attachment and fixed frequency settings. Each muscle group will be treated for approximately 30–60 seconds, resulting in a total session duration of 5–7 minutes. The Post-Isometric Relaxation (PIR) intervention will be applied to the hamstrings, quadriceps femoris, and gastrocnemius muscles. Each PIR cycle will consist of a submaximal isometric contraction (20–30% of perceived maximal effort) maintained for 5–7 seconds, followed by brief relaxation and a passive stretch held for 10–15 seconds. Two to three cycles will be performed per muscle group. The total PIR session duration will be approximately 8–10 minutes. All procedures will be conducted within pain-free ranges of motion under professional supervision. In the flossing intervention arm, an elastic compression band will be applied circumferentially to the proximal thigh of the dominant limb using standardized moderate compression. During the 1–2 minute compression phase, participants will perform controlled active movements, including bodyweight squats, forward and backward lunges, active knee flexion-extension, and ankle plantarflexion-dorsiflexion. Movements will be executed continuously at a standardized tempo. The total flossing intervention time will be approximately 5–7 minutes per session. The Tension Releasing Exercises (TRE) intervention will follow a standardized protocol designed to induce neurogenic tremor activity and facilitate reduction of excessive muscle tone. After a brief preparatory phase involving low-intensity lower limb activation, participants will assume positions that promote involuntary tremor responses primarily in the pelvic and thigh musculature. The tremor phase will last approximately 15–20 minutes in supine or semi-supine positions. Sessions will be supervised to ensure correct positioning, comfort, and safety. Outcome assessments will be conducted at baseline and after completion of the 12-week intervention period. Primary and secondary measures will include neuromuscular reaction time assessed via sEMG, postural stability evaluated through COP analysis on a force platform, body composition assessed using bioelectrical impedance analysis, and movement quality evaluated using the Y-Balance Test (YBT) and the Functional Movement Screen (FMS).