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

Effects of an 8-Week CrossFit-Based Concurrent Training Program on Physical Fitness, Body Composition, and Psychological Outcomes in Schoolchildren: A Randomized Controlled Trial Protocol

This study examines the effects of an 8-week CrossFit-based concurrent training program in boys and girls aged 7 to 11 years, comparing an experimental group (n=15) with a control group (n=15). The aim is to assess changes in strength, cardiorespiratory fitness, body composition, and psychological variables such as anxiety, stress, and self-esteem, using field-based physical tests (CMJ, Course Navette, handgrip strength, etc.) and validated questionnaires. The study follows a randomized controlled trial design with pre- and post-intervention assessments. The experimental group will complete two weekly CrossFit sessions adapted for children, while the control group will maintain their usual routine without structured physical training. The hypothesis states that the intervention will significantly improve both physical performance and psychological well-being in the experimental group compared to the control group.

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.

Inclusion Criteria:

• Age: 7-11 years.
• Students enrolled at CEIP Pablo García Baena (Córdoba).

For the experimental group:

• Availability to attend the Triple XXX Box (Polígono Pedroches, C. los Alfareros, Parcel 119, 14014 Córdoba), where both assessments and training sessions will be conducted.
• Availability to attend training sessions twice per week for the 8-week intervention period.
• No participation in extracurricular physical activity prior to the start of the CrossFit program.

For the control group:

No participation in extracurricular physical activity. Informed consent signed by parents or legal guardians. No medical, psychological, or behavioral contraindications that would prevent participation in physical activity.

Exclusion Criteria:

• Children with musculoskeletal injuries, diseases, or medical, psychological, or behavioral conditions that limit physical activity or interfere with the assessment of outcomes.
• Inability or anticipated difficulty in regularly attending training sessions.
• Refusal of parents or legal guardians to provide informed consent.