Purpose The present study examined the influence of endurance training on the morphological and functional heart adaptations in young athletes throughout a longitudinal 9-month follow-up period during the adolescent peak height velocity (PHV). Methods Thirty-six 13- to 15-year-old males (twenty-three triathletes and thirteen untrained peers) were evaluated before and after a 9-month period during PHV. Maximal oxygen uptake (VO2max) and power at VO2max were assessed during incremental cycling test. Resting echocardiography was performed to evaluate left ventricular (LV) morphology with standard parameters and using an original approach to assess LV shape. In addition, LV function was evaluated with advanced echocardiography tools including LV strains and myocardial work analyses from speckle-tracking echocardiography. Results Absolute VO2max increased similarly in both groups but power at VO2max only significantly increased in triathletes (from 232 ± 46 to 264 ± 46 W, p < 0.001). Maturation had a significant effect on LV morphology with an enlargement in both groups. Endurance training induced additional adaptations in young triathletes, i.e., a cardiac remodeling characterized by an increase in LV length (from 7.5 ± 0.7 to 8.2 ± 0.6 cm, p < 0.01). The stroke volume was greater in young triathletes compared to untrained peers but with a constant difference throughout the 9-month period. Finally, speckle-tracking echocardiography and myocardial work remained unchanged during the follow-up and similar between groups. Conclusion Endurance training induced morphological adaptations during the PHV period without significant adaptation in LV function as evidenced by the absence of specific changes in LV strains and myocardial work.
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