This randomized single-blind crossover trial investigated the acute effects of three different exercise modalities, namely self-myofascial release with a foam roller, dynamic stretching, and static stretching, on posture, flexibility, dynamic balance, and lower-extremity performance in adolescent karate athletes (12-18 years). Participants attended four weekly sessions at the same time of day and after a 48-hour rest period. In the first week a baseline (control) measurement was performed, and in the following three weeks each participant received the three interventions in a randomized order. Outcomes included a four-view smartphone-based posture analysis (PostureScreen Mobile), the Sit-and-Reach Test, the Y Balance Test, the 30-second Sit-to-Stand Test, and the Vertical Jump Test (My Jump Lab 2). The aim was to identify which warm-up modality offers the greatest acute benefit before karate-specific performance

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.

Inclusion Criteria:

• Age 12-18 years.
• Active karate training of at least 4 days per week and at least 10 hours per week.
• Ability to communicate in Turkish or English (written and verbal).
• Written informed assent of the participant and informed consent of the parent/legal guardian.

Exclusion Criteria:

• Any systemic, orthopedic, neurologic, chronic or psychiatric disease.
• Any health problem precluding regular training participation.
• Long-term steroid use.
• Use within the past 48 hours of medications known to influence musculoskeletal performance.
• During the study: pain greater than 3/10 on the VAS, intercurrent illness or injury, or participant request to withdraw.

Every participant complete all interventions with different order. They only informed about all interventions causes relaxation on muscles. Thet don't informed about which one is probably more effective.