Effects of 8-Week CrossFit-Based Concurrent Training on Fitness, Body Composition, and Psychological Outcomes in Schoolchildren

This study is a randomized controlled trial designed to examine the effects of an 8-week CrossFit-based concurrent training program on both physical fitness and psychological well-being in school-aged children (boys and girls aged 7 to 11 years). The sample will be drawn from a primary school in Córdoba (Spain) and will be randomly assigned to either an experimental group (n=15) or a control group (n=15). The experimental group will participate in a supervised CrossFit Kids program, consisting of two weekly sessions of 50 minutes each. These sessions will include functional, age-appropriate high-intensity exercises structured into four parts: warm-up (mobility and games), strength work (technical and developmental exercises), metabolic conditioning (METCON), and a final cool-down or game-based activity. The control group will continue with their usual daily routine without any structured physical training during the intervention period. The study will assess changes in physical fitness variables, including muscular strength (countermovement jump, handgrip strength, standing long jump, and medicine ball throw), cardiorespiratory fitness (Course Navette test, burpees, abdominal endurance tests, and step tests), and body composition indicators such as BMI, waist circumference, and waist-to-height ratio. In addition, psychological outcomes will be evaluated using validated instruments measuring state and trait anxiety (State-Trait Anxiety Inventory), daily stress (Children's Daily Stress Inventory) and self-esteem (Rosenberg Self-Esteem Scale). Measurements will be taken before and after the intervention to compare intra- and inter-group changes. The study also explores potential relationships between improvements in physical fitness and psychological outcomes. The main hypothesis is that participation in the CrossFit-based concurrent training program will lead to significant improvements in strength, endurance, body composition, and psychological well-being (reduced anxiety and stress and improved self-esteem) compared to the control group, highlighting the potential of this training approach as an effective and comprehensive intervention for children.