Individual Response Variability to Acute Post-Activation Performance Enhancement(PAPE) in Elite Athletes: a Multifactorial Prediective Modeling and Intelligent Intervention Strategy Study

INTERVENTION: Group 1: Caffeine + Placebo Group:Randomized double‐blind two‐period crossover design; the washout period was 7 days. The subjects were randomly assigned to one of the two dosing sequences: Group 1: took caffeine capsules (3 mg/kg body weight) in the first period, and took the same amount of placebo capsules (starch) in the second period. Both periods followed the individualized depth jump activation protocol and the CMJ test.;Group 2: Placebo + Caffeine Group:Randomized double‐blind two‐period crossover design; the washout period was 7 days. The subjects were randomly assigned to one of the two dosing sequences: Group 2: took placebo capsules (starch) in the first period, and caffeine capsules (3 mg/kg body weight) in the second period. Both periods involved the individualized depth jump activation protocol and the CMJ test.; CONDITION: None PRIMARY OUTCOME: countermovement jump, CMJ;Optimal PAPE enhancement (?best);Optimal PAPE response time point (Tbest);Mean PAPE enhancement / Area under the curve (AUC); SECONDARY OUTCOME: Rating of perceived exertion (RPE) at each time point;Heart rate (HR) at each time point;One‐repetition maximum (1RM) squat;Body composition (DEXA);Questionnaire indicators related to long‐term background and current status;Body circumferences and lower‐limb morphological indices; INCLUSION CRITERIA: 1. A total of 60 participants, including both males and females, aged 18–35 years, will be recruited. 2. Participants must be in good health, with no diagnosed cardiovascular, respiratory, neuromuscular, musculoskeletal, or other diseases or health conditions that would contraindicate participation in exercise testing. 3. Participants must possess a certain level of athletic background, with at least 6 years of training experience and a National Grade II Athlete Certificate or above. They must be capable of safely completing standardized warm‐up procedures, conditioning activities (CA), and countermovement jump (CMJ) tests under the guidance of the researchers. 4. Participants must be willing to complete the entire experimental protocol in accordance with the study requirements, including two laboratory visits as well as the completion of relevant questionnaires and record forms. 5. Participation in this study must be voluntary, and all participants must