A history of back pain during adulthood is related to a history of back pain during adolescence. Therefore, preventing back pain in adolescents helps to prevent their appearance in adulthood. Sagittal spinal misalignments and stability of the spine are in connection with back pain in adolescents. In addition, they influence on several spinal pathologies and decrease the functional capacity and quality of life of adolescents. Therefore, the objectives of the following project were: a) assess back pain in schoolchildren and check their relationship with quality of life, sagittal spine curvature, extensibility of the hamstring muscles, sedentary lifestyle, physical activity, BMI , percentage of body fat and the waist-hip index; b) measure the sagittal spinal curvature of the schoolchildren, the quality of life and the prevalence of physical activity among adolescents and check their relationship with the hamstring extensibility, sedentary lifestyle, the BMI , percentage of body fat and the waist-hip index; c) analyze the effect of a 10-minute Pilates program carried out in the final part of the Physical Education sessions for 4.5 months and 9 months on back pain, quality of life, sagittal spinal curvatures, the hamstring flexibility, the BMI, the percentage of body fat and the waist-hip index. The present investigation will be elaborated by a quasi-experimental design, with experimental group (GE) and control group (CG); with pretest, intermediate and post-test, with analysis of intra-group and inter-group measurements for each of the dependent variables selected in the study. The inclusion criteria will be: a) being in Compulsory Secondary Education; b) not present 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. It was assessed back pain with Back Pain Survey in adolescents. Quality of life was assessed through the Kidscreen-27 questionnaire. To assess the sagittal spinal curvatura (in several position) the Spinal Mouse System (Idiag, Fehraltdorf, Switzerland) was used. The extensibility of hamstring muscle was assessed with seat and reach test, toe touch test and active and passive straight leg raising test. The sedentary lifestyle as well as the level of physical activity will be evaluated through the Adolescent International Physical Activity Questionnaire (IPAQ). The body mass index will be obtained by recording weight and height (BMI = Weight (kg) / height (cm) 2).

The waist-hip ratio is the quotient between waist and hip circumferences, which is an indirect marker of intra-abdominal obesity.

The intervention program consisted in the realization of exercises of the Pilates Method during the sessions of Physical Education. The duration of the program will be 32 weeks, with a frequency of two weekly sessions and a duration per intervention of 10 minutes. During this time the experimental group developed the intervention program with the Pilates Method and the control group carried out their usual sessions of Physical Education . All students to be taken into account in the research must have attended and conducted the practice at least 80% of sessions. The program consisted of four Pilates exercises, planned with a basic-intermediate level, gradually incorporating the Principles of the Pilates Method and increasing the intensity of the exercises. Among these four exercises, two focus on the work of the resistance of the flexor muscles of the trunk, one in the work of the resistance of the trunk extensor musculature and another in the work of hamstring extensibility.The exercises will be performed in cool down of the sessions of Physical Education.