Effects of Microdosed Resistance Training During Physical Education on Health-Related Fitness in Adolescents

This study will examine whether short bouts of resistance training incorporated into physical education lessons can improve health-related physical fitness in secondary school students aged 15-16 years. A total of 264 students will participate in two successive cohorts. School classes, rather than individual students, will be randomly assigned to study groups. In the first cohort, three resistance-training programs using low, moderate, or high training loads will be compared with usual physical education. The program producing the most consistent beneficial changes will then be tested in a new group of students in the second cohort and compared with usual physical education. Each training program will last eight weeks. Participants will be assessed before the intervention, halfway through it, immediately after it, and eight weeks after it ends. Assessments will include body composition, blood pressure, cardiorespiratory fitness, muscular fitness, jumping performance, trunk muscular endurance, and sprint performance. The study will evaluate both average changes in each group and the proportion of students showing improvements greater than the expected measurement error of the tests.

Inclusion Criteria: * Enrollment in the second year of a participating secondary school. * Participation in regular physical education lessons at the participating school. * No health contraindications to physical exercise. * Written informed consent from the participant and, for participants who are minors, written informed consent from a parent or legal guardian. Exclusion Criteria: * Acute or chronic musculoskeletal injury preventing safe participation in the exercise intervention or physical fitness assessments. * Chronic disease or other medical condition constituting a contraindication to physical exercise. * Medical recommendation limiting participation in physical activity. * Acute infection or other temporary health condition preventing safe participation in a scheduled assessment. * Lack of the required informed consent.