High intensity interval training intervention within physical education class on health-related fitness in children aged 10 to 15

This intervention will be introduced to one primary school in the city of Zagreb, Croatia during the second semester of a school year 2021/2022. The intervention will provide two high intensity interval training sessions per week embedded in Physical Education classes to children aged 10 to 15. High intensity interval training will last 10 minutes per Physical Education session. Petra Juric, mag. cin. will implement the intervention and will be fully involved in the implementation process. Associates (blinded from group allocation) from the Faculty of Kinesiology will carry out initial and final measurements. The measurements before the beginning of the intervention, and at the end of the intervention, after 12 weeks. Regarding the transfer of instruments, they will be calibrated before each new cycle of use, while the transfer itself will be performed with precautions to minimize the possibility of damage. Intention to treat principle will be implemented meaning that no students will be excluded from the study unless they actively withdraw from the study after consenting. As part of the informed consent process, a health status report is submitted by the parent and is determined by the family doctor. The main information on the child's health status will be collected simultaneously with parental consent regarding research participation. The main target objective of the high intensity interval training within the Physical Education lessons will be the improvement of physical fitness scores based on EUROFT measures and reduced adiposity. The intervention will last three months, during the second semester of the school year 2021/2022. Approximately 100 students will be included in the intervention. There are approximately 25 students in each Physical Education class in most primary schools so that means we will have four intervention classes. Students in the intervention group who will participate at a minimum of 80% of Physical Education classes will be included in the data analysis. The intervention group will be introduced high intensity interval training program at the beginning of each Physical Education lesson. High intensity interval training will be conducted progressively over 12 weeks, with an increase in intensity according to the abilities of children and adolescents. One stimulus will consist of the following: preparation phase lasting 2 minutes, passive rest lasting 30 seconds, first working phase lasting 2 minutes, second passive rest lasting 30 seconds, second working phase lasting 2 minutes, and active rest lasting 2 minutes. Several variations of stimuli will be applied cyclically, to keep children and adolescents interested and motivated. During passive rest, the heart rate will be estimated in a standing position for 6 seconds, which will be subsequently multiplied by 10. Based on this, the load level will be monitored, where children and adolescents will have one introduction session before the start of the intervention to learn how to self-assess heart rate and get acquainted with the settings of the intervention that will be carried out. Since there are many holidays during the second semester of the school year 2021/2022, children will not do high intensity interval training sessions during this period. They will continue with the intervention after returning to school, with a total of 24 stimuli during 12 weeks while being present at the school. Eurofit Fitness test battery will be used for evaluating effects of an intervention. Exercises will be: Example 1 Prep phase: Jumping Jacks x 10; Running in Place x 10; Rhythmic Jumping x 10; Repeat until time is up Passive recovery 1: Standing still take pulse (6 seconds x 10) Working phase 1: Push-ups x 10; 5m Shuttle Sprint x 10; Squats x 10; 5m Shuttle Sprint x 10; Repeat until time is up Passive recovery 2: Standing still take pulse (6 seconds x 10) Working phase 2: Twisting Push-ups x 10; 5m Shuttle Sprint x 10; Plank Leg Raises x 10 5m Shuttle Sprint x 10; Repeat until time is up Active recovery: Dynamic/static stretching w Teacher returns to the normal teaching program for the remaining lesson time Example 2 Prep phase: Diamond Jumps x 10; High Knee Runs x 10; Speed Skaters x 10; Repeat until time is up Passive recovery 1: Standing still take pulse (6 seconds x 10) Working phase 1: Chair Triceps Dips x 10; 5m Shuttle Sprint x 10; Reverse Lunge x 10; 5m Shuttle Sprint x 10; Repeat until time is up Passive recovery 2: Standing still take pulse (6 seconds x 10) Working phase 2: Plank to Push-ups x 10; 5m Shuttle Sprint x 10; V-Sit x 10; 5m Shuttle Sprint x 10; Repeat until time is up Active recovery: Dynamic/static stretching Teacher returns to the normal teaching program for the remaining lesson time Example 3 Prep phase: Power Jumping x 10; Mountain Climbers x 10; Tuck Jumps x 10; Repeat until time is up Passive recovery 1: Standing still take pulse (6 seconds x 10) Working phase 1: Twisting Push-ups x 10; 5m Shuttle Sprint x 10; Plank Leg Raises x 10; 5m Shuttle Sprint x 10; Repeat until time is up Passive recovery 2: Standing still take pulse (6 seconds x 10) Working phase 2: Push-ups x 10; 5m Shuttle Sprint x 10; Squats x 10; 5m Shuttle Sprint x 10; Repeat until time is up Active recovery: Dynamic/static stretching Teacher returns to the normal teaching program for the remaining lesson time Example 4 Prep phase: Squat Jumps x 10; Burpees x 10; Plank Jacks x 10; Repeat until time is up Passive recovery 1: Standing still take pulse (6 seconds x 10) Working phase 1: Plank to Push-ups x 10; 5m Shuttle Sprint x 10; V-Sit x 10; 5m Shuttle Sprint x 10; Repeat until time is up Passive recovery 2: Standing still take pulse (6 seconds x 10) Working phase 2: Chair Triceps Dips x 10; 5m Shuttle Sprint x 10; Reverse Lunge x 10; 5m Shuttle Sprint x 10; Repeat until time is up Active recovery: Dynamic/static stretching Teacher returns to the normal teaching program for the remaining lesson time Participants will not be asked to aim for a pre-specified level of intensity during the intervention sessions. If a student is able to increase the frequency of a specific exercise performance, he or she will do it. If a student feels he or she cannot increase the frequency, he or she will remain doing an exercise at a slower rate. A strategy which will be used to monitor adherence to the intervention will be class attendance rolls.