Regular physical activity and supervised strength training are recognized components of healthy growth and motor development during childhood. Although linear and nonlinear periodized strength training are widely used approaches for organizing resistance training, limited information is available regarding their comparative application in school-aged children, particularly within school-based programs. This randomized controlled trial compares two periodized strength training models implemented over a 20-week intervention in schoolchildren to assess muscular power and speed/agility using standardized motor performance assessments.

Regular physical activity is an essential component of healthy growth and development during childhood. Current physical activity recommendations encourage children to participate in daily moderate-to-vigorous physical activity that includes muscle- and bone-strengthening activities several times per week. Within this context, supervised strength training represents a structured form of physical activity that can be incorporated into school-based exercise programs.

Adaptations to strength training are influenced by the organization of training variables, including intensity, volume, frequency, density, exercise selection, and progression. These variables are systematically manipulated through periodization to organize training across an intervention. Two of the most frequently used periodization strategies are linear periodization, characterized by progressive increases in training intensity accompanied by reductions in training volume, and nonlinear periodization, in which training variables are modified more frequently throughout the training program.

Although both periodization models are commonly applied in resistance training, comparatively few investigations have evaluated their application in school-aged children. Existing studies have primarily involved young athletes or sport-specific populations, and information regarding the comparative use of linear and nonlinear periodization in school-based interventions remains limited. Additional randomized controlled trials are needed to evaluate these programming strategies in children using standardized measures of motor performance.

This study is a 20-week randomized controlled trial conducted in schoolchildren. Participants are randomly assigned to one of three groups: a linear periodization group, a nonlinear periodization group, or a control group that continues regular physical education classes. The intervention consists of three supervised strength training sessions per week for the intervention groups.

Motor performance is assessed before and after the intervention using standardized field-based tests of lower-body muscular power, upper-body muscular power, sprint performance, and agility. Comparisons are performed between the linear periodization group, the nonlinear periodization group, and the control group according to the study protocol.

Inclusion Criteria:

• Schoolchildren enrolled in one of the participating educational institutions.
• Approximately 12-13 years of age.
• Willing to participate in the study.
• Written informed consent provided by parents or legal guardians.
• Availability to participate in all assessment sessions.

Exclusion Criteria:

• Medical history that prevented participation in sports practice (cardiovascular disease, neurological disease, or chronic respiratory disease).
• Musculoskeletal injuries and/or bone malformations at the time of the study.
• Recent injury before study participation.
• Absence during pre-test or post-test assessments.
• Failure to attend at least 80% of the intervention sessions (experimental groups).
• Participation in systematic physical activity or organized sports outside the school setting.
• Lack of written parental or legal guardian consent.

Individual participant data will not be shared in order to protect participant confidentiality and privacy and because no data-sharing plan was established in the study protocol or informed consent process.