Purpose. Exercise performed improperly, in disagreement with age and development, may trigger negative bioactive effects. Adolescent taekwondo athletes, being able to practise on tatami or without tatami and barefoot, may be submitted to musculoskeletal structure disorders. the purpose of this study was to describe the frequency and amplitude of the reactive forces during taekwondo practice with and without tatami. Methods. Overall, 27 adolescent taekwondo athletes aged 10-15 years were submitted to a standard 90-minute training session with and without tatami. During each session, the frequency of ground contacts and the vertical ground reaction forces were measured. Femur and wrist bone age and the respective stages of the epiphyseal plate were computed from radiograph images. A total of 6346.6 ± 425.5 ground contacts (an average of 106 contacts per minute) were registered during the training session. the Wilcoxon test was applied to analyse the relationship between taekwondo and epiphyseal plate stage (p 0.005). Results. Student's t-test revealed a significant difference between ground reaction forces with and without tatami; tasks performed without tatami featured smaller magnitudes for comparisons of absolute and normalized values (t = -3.359; p < 0.002 and t = -3.652; p < 0.001, respectively). the time of practice showed no early closure of the femur epiphyseal plates caused by the practice of taekwondo. Conclusions. Practising taekwondo seems to have a bio-positive effect on the maturation of adolescent athletes, regardless of the use of tatami.