title: Athletic training affects the uniformity of muscle and tendon adaptation during adolescence.
abstract: With the double stimulus of mechanical loading and maturation acting on the muscle-tendon unit, adolescent athletes might be at increased risk of developing imbalances of muscle strength and tendon mechanical properties. This longitudinal study aims to provide detailed information on how athletic training affects the time course of muscle-tendon adaptation during adolescence. In 12 adolescent elite athletes (A) and 8 similar-aged controls (C), knee extensor muscle strength and patellar tendon mechanical properties were measured over 1 yr in 3-mo intervals. A linear mixed-effects model was used to analyze time-dependent changes and the residuals of the model to quantify fluctuations over time. The cosine similarity (CS) served as a measure of uniformity of the relative changes of tendon force and stiffness. Muscle strength and tendon stiffness increased significantly in both groups (P < 0.01). However, the fluctuations of muscle strength were greater [A, 17 ± 7 (SD) N·m; C, 6 ± 2 N·m; P < 0.05] and the uniformity of changes of tendon force and stiffness was lower in athletes (CS A, -0.02 ± 0.5; C, 0.5 ± 0.4; P < 0.05). Further, athletes demonstrated greater maximum tendon strain (A, 7.6 ± 1.7%; C, 5.5 ± 0.9%; P < 0.05) and strain fluctuations (A, 0.9 ± 0.4; C, 0.3 ± 0.1; P < 0.05). We conclude that athletic training in adolescence affects the uniformity of muscle and tendon adaptation, which increases the demand on the tendon with potential implications for tendon injury.
authors: Humboldt-Universität zu Berlin, Department of Training- and Movement Sciences, Berlin, Germany; and Berlin School of Movement Sciences, Berlin, Germany.
authors: Falk
authors: F
authors: Mersmann
authors: Humboldt-Universität zu Berlin, Department of Training- and Movement Sciences, Berlin, Germany; and Berlin School of Movement Sciences, Berlin, Germany.
authors: Sebastian
authors: S
authors: Bohm
authors: Humboldt-Universität zu Berlin, Department of Training- and Movement Sciences, Berlin, Germany; and Berlin School of Movement Sciences, Berlin, Germany.
authors: Arno
authors: A
authors: Schroll
authors: Humboldt-Universität zu Berlin, Department of Training- and Movement Sciences, Berlin, Germany; and Berlin School of Movement Sciences, Berlin, Germany.
authors: Robert
authors: R
authors: Marzilger
authors: Humboldt-Universität zu Berlin, Department of Training- and Movement Sciences, Berlin, Germany; and Berlin School of Movement Sciences, Berlin, Germany a.arampatzis@hu-berlin.de.
authors: Adamantios
authors: A
authors: Arampatzis
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000293:Adolescent; D055119:Elastic Modulus / Q000502:physiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D064797:Physical Conditioning, Human / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013177:Sports / Q000502:physiology*; D013314:Stress, Mechanical; D013710:Tendons / Q000502:physiology*; D013718:Tensile Strength / Q000502:physiology
keywords: adolescence; biomechanics; knee; plasticity; tendinopathy; time course