Design: This study was a randomized, single-blind, three-period crossover trial conducted at the Usak Karate Ozlem Sport Club, Usak, Turkiye. Adolescent karate athletes aged 12-18 years training at least 4 days/week and a minimum of 10 hours/week were eligible. After signing the assent and parental informed consent forms, participants were randomly allocated to one of three treatment-order sequences using sealed opaque envelopes. Procedures: All assessments and interventions were carried out by the same physiotherapist on the same day of the week, with one-week wash-out periods between sessions, and after a 48-hour abstention from training in order to capture purely acute effects. Week 1 served as the control measurement (no intervention). In Weeks 2-4, the three interventions (static stretching, dynamic stretching, self-myofascial release) were applied in a randomized order; outcome measures were repeated immediately after each intervention with a standardized 2-minute rest interval. Interventions: (1) Static stretching: 30-second hold per muscle group (knee flexors, knee extensors, hip extensors), 5 repetitions, with 15-second inter-set rest. (2) Dynamic stretching: walking knee-to-chest, walking quadriceps stretch (heel-to-buttock), and walking straight-leg kicks; each performed for 30 seconds (one repetition every 2 seconds), 5 sets with 15-second inter-set rest. (3) Self-myofascial release (SMR): EVA medium-density foam roller applied to knee extensors, knee flexors, and hip extensors; 5 sets of 30 seconds at 40-60 bpm rolling cadence per muscle group. Outcome assessment: Posture was evaluated with the PostureScreen Mobile (PSM) application using anterior, posterior, right and left lateral photographs and analyzing head, shoulder, pelvis and knee anterior/lateral translations. Flexibility was assessed using the Sit-and-Reach Test on a standard reach box. Dynamic balance was assessed with the Y Balance Test (anterior, posteromedial, posterolateral reach distances normalized to leg length) on both lower extremities. Lower-extremity muscular endurance was assessed with the 30-second Sit-to-Stand Test. Vertical jump performance was measured using the My Jump Lab 2 smartphone application with a tripod-fixed iPhone camera. Statistical analysis: A priori power analysis was performed using G\*Power 3.1 (effect size f = 0.25, alpha = 0.05, power = 0.95) which yielded a minimum required sample of 36 participants; 48 athletes were enrolled to account for potential drop-outs. Normality was tested with the Shapiro-Wilk test. Because data were not normally distributed, the Friedman test was used for within-subject comparisons, with Wilcoxon signed-rank tests applied for pairwise post-hoc analyses. A change-score (delta) analysis was used to compare interventions head-to-head. Statistical analyses were performed using IBM SPSS 25.0 with significance set at p\<0.05. There was no external funding for the study and the authors declared no conflicts of interest.
