Several risk factors associated with cardiovascular disease could be prevented or treated by means of physical activity from childhood. Among the physical exercise programs for the improvement of these variables we can highlight high-intensity interval training. However, most of these studies have been carried out on overweight or obese athletes or schoolchildren and existing protocols on high intensity intervallic training are different. The main objective of the present research is to compare two high-intensity intervallic training protocols on body composition, heart rate, blood pressure, lipid profile, blood glucose, cardiovascular fitness, strength, quality of life, physical activity, enjoyment of physical activity and accident proneness in adolescents. The present investigation will be elaborated by a randomized-control trial design, with 2 experimental groups and a control group (CG). In each experimental groups a different protocol of high-intensity interval training is applied.

It is assessed cardiovascular capacity and strength. Body composition is assessed. Heart rate and blood pressure were also recorded. Lipid profile and blood glucose were obtained by blood sampling. Quality of life, sedentary and physical activity lifestyle, enjoyment of physical activity and Psychoeducational factors determining accident process are assessed.

Cardiovascular diseases are the leading cause of death today. These have been inversely correlated with physical activity and fitness in adults, children and adolescents. In this sense, certain risk factors associated with cardiovascular disease could be prevented or treated by means of physical activity from childhood. Traditionally, the benefits of physical activity on cardiovascular markers and physical fitness in children and adolescents have been described in research conducted with traditional aerobic exercise programs. Among the physical exercise programs for the improvement of these variables we can highlight high-intensity interval training. However, most of these studies have been carried out on overweight or obese athletes or schoolchildren. On the other hand, the existing protocols on high intensity intervallic training are different, there have been intensive and extensive protocols. Likewise, the investigations do not usually control the real intensity of work and it has been described that in most cases the participants do not manage to reach the described intensity, which indicates that they are not working at the level that is considered or they are working with an intensity of an extensive protocol while the duration is of an intensive protocol. In this sense, the objective of the present research is a) to know the effect of high intensity intervallic training on body composition, heart rate, blood pressure, lipid profile, glycemia, cardiovascular capacity, strength, quality of life, physical activity, enjoyment of physical activity and accident proneness in adolescents and b) to compare two high-intensity intervallic training protocols on body composition, heart rate, blood pressure, lipid profile, blood glucose, cardiovascular fitness, strength, quality of life, physical activity, enjoyment of physical activity and accident proneness in adolescents.

The present investigation will be elaborated by a randomized-control trial design, with 2 experimental groups and a control group (CG); with pre-test and post-test. Each experimental groups performance differences protocol of high-intensity interval training.

The inclusion criteria will be: a) being in Compulsory Secondary Education; b) not presenting any musculoskeletal, neurological, cardiological, metabolic, rheumatic or previous history of spinal pathologies or with previous treatment; c) be active in the sessions of Physical Education.

Primary outcome measure are cardiovascular capacity, strength of upper limbs and strength of lower limbs. These variables are tested with "Course Navette test", handgrip dynamometry and long jump test, respectively.

Secondary outcome measure are body composition and its assessed by height, weight, waist circumference, fat percentage, hydration, muscle mass, bone weight and visceral fat. The body mass index will be obtained by recording weight and height (BMI = Weight (kg) / height (cm) 2). Heart rate and blood pressure were also recorded. Lipid profile (high density lipoproteins, low density lipoproteins and triglycerides) and blood glucose were obtained by blood sampling. Quality of life are assessed through the "Kidscreen-27 questionnaire". The sedentary lifestyle as well as the level of physical activity will be evaluated through the Adolescent International Physical Activity Questionnaire (IPAQ).

The enjoyment of physical activity and a questionnaire on Psychoeducational factors determining accident proneness in adolescents were assessed.

Intensity was assessed during all sessions by means of a heart rate monitor for each adolescent.

The type of activity used to develop the training was continuous running. After the usual warm-up in physical education classes, one of the two high-intensity interval training protocols was applied. Both have the same work time but distributed in different ways and with different intensities.

The intensive high intensity intervallic training group performs 6 sets of 60 seconds of work and 60 seconds of rest. During the first two weeks we work at an intensity of 80-85% of the reserve heart rate during the work phase and 50-55% of the reserve heart rate during the rest time. In weeks 3 and 4 the intensity in the work phase is increased by 5%, reaching from the fifth week onwards a work intensity of 95-95% of the reserve heart rate.

The extensive high-intensity intervallic training group performs 3 sets of 120 seconds of work and 120 seconds of rest at an intensity of 70-75% of the reserve heart rate during the work phase and an intensity of 50-55% of the reserve heart rate during the rest phase. In weeks 3 and 4 the intensity in the work phase is increased by 5%, reaching from the fifth week onwards a work intensity of 80-85% of the reserve heart rate.

The program duration is 8 weeks and the frequency of intervention is 2 sessions per week.

Inclusion Criteria:

• being in Compulsory Secondary Education
• be active in the sessions of Physical Education

Exclusion Criteria:

• presenting any musculoskeletal, neurological, cardiological, metabolic, rheumatic or previous history of spinal pathologies or with previous treatment