Calisthenics-Based Intervention in Adolescents: Effects on Strength, Body Composition, Eating Habits, and Self-Concept (CALI-TEENS)

Study Design This is a randomized, parallel-group, controlled trial designed to assess the effects of a school-based calisthenics intervention on physical fitness, body composition, dietary habits, and self-concept in adolescents. Participants will be randomly assigned in a 1:1 ratio to an experimental group or a control group.

Study Setting The study will be conducted at a public secondary school in Turmequé, Boyacá, Colombia, involving ninth-grade students.

Participants A total of 120 adolescents aged between 13 and 16 years will be recruited. Eligibility will be determined based on predefined inclusion and exclusion criteria. Written informed consent from parents or legal guardians and assent from participants will be obtained prior to enrollment.

Randomization and Allocation Participants will be assigned to study groups using a computer-generated randomization sequence. Allocation will be conducted by an independent individual not directly involved in the study procedures to minimize selection bias. Due to the nature of the intervention, participant blinding is not feasible.

Intervention The experimental group will participate in a structured calisthenics program integrated into physical education classes over a 12-week period. The program consists of three weekly sessions of approximately 60 minutes each.

Each session will include the following components:

• Warm-up phase (mobility and dynamic stretching)
• Main exercise phase, including six bodyweight exercises targeting upper body, lower body, or full-body strength
• Cool-down phase with static stretching and relaxation exercises

The intervention follows a progressive overload model:

Exercise duration will increase over time (from 60 to 90 seconds per exercise) Rest intervals between sets will decrease progressively (from 40 to 15 seconds) Effort intensity will be monitored using the Borg Rating of Perceived Exertion scale

Sessions will be conducted in school facilities, including outdoor spaces and sports courts, under the supervision of a qualified instructor to ensure safety and proper execution.

Control Group Participants in the control group will continue with their standard physical education curriculum, which includes activities such as volleyball and handball, according to the institutional academic plan.

Outcome Measures Assessments will be conducted at baseline (week 0) and post-intervention (week 13).

Primary Outcomes

- Muscle strength: measured using a digital handgrip dynamometer

Secondary Outcomes

• Body composition: assessed through anthropometric measurements and skinfold thickness to estimate body fat percentage and body mass index
• Dietary habits: evaluated using a validated food frequency questionnaire
• Self-concept: assessed using the Self-Concept Form-5 (AF5), which measures multiple dimensions including physical self-perception

Sample Size Calculation The sample size was calculated to detect a meaningful difference in strength outcomes between groups, assuming a standard deviation of 15 units, with 90% power and a 5% significance level. A minimum of 60 participants per group is required.

Statistical Analysis Descriptive statistics will be calculated for all variables. Normality will be assessed using the Kolmogorov-Smirnov test. A two-way analysis of variance (ANOVA) will be performed to examine the effects of time, group, and their interaction. Bonferroni post hoc tests will be applied where appropriate. Statistical significance will be set at p < 0.05.

Data Management Participant data will be coded to ensure confidentiality. Only authorized research personnel will have access to the dataset. Data will be stored securely and managed in accordance with data protection regulations.

Ethical Considerations The study will be conducted in accordance with the principles of the Declaration of Helsinki and applicable national and international regulations. The study involves minimal risk, as it consists of supervised physical activity within a school setting. Participants will be informed that their participation is voluntary and that they may withdraw at any time without consequences.

Expected Impact This study aims to provide evidence on the effectiveness of calisthenics as a low-cost, accessible intervention to promote physical activity and improve health outcomes in adolescents. The results may contribute to the development of innovative physical education strategies and inform public health policies targeting youth populations.