title: Human Achilles tendon plasticity in response to cyclic strain: effect of rate and duration.
abstract: High strain magnitude and low strain frequency are important stimuli for tendon adaptation. Increasing the rate and duration of the applied strain may enhance the adaptive responses. Therefore, our purpose was to investigate the effect of strain rate and duration on Achilles tendon adaptation. The study included two experimental groups (N=14 and N=12) and a control group (N=13). The participants of the experimental groups exercised according to a reference protocol (14 weeks, four times a week), featuring a high strain magnitude (~6.5%) and a low strain frequency (0.17 Hz, 3 s loading/3 s relaxation) on one leg and with either a higher strain rate (one-legged jumps) or a longer strain duration (12 s loading) on the other leg. The strain magnitude and loading volume were similar in all protocols. Before and after the interventions, the tendon stiffness, Young's modulus and cross-sectional area were examined using magnetic resonance imaging, ultrasound and dynamometry. The reference and long strain duration protocols induced significantly increased (P<0.05) tendon stiffness (57% and 25%), cross-sectional area (4.2% and 5.3%) and Young's modulus (51% and 17%). The increases in tendon stiffness and Young's modulus were higher in the reference protocol. Although region-specific tendon hypertrophy was also detected after the high strain rate training, there was only a tendency of increased stiffness (P=0.08) and cross-sectional area (P=0.09). The control group did not show any changes (P=0.86). The results provide evidence that a high strain magnitude, an appropriate strain duration and repetitive loading are essential components for an efficient adaptive stimulus for tendons.
authors.affiliation: Humboldt-Universität zu Berlin, Department of Training and Movement Sciences, 10115 Berlin, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Bohm
authors.affiliation: Humboldt-Universität zu Berlin, Department of Training and Movement Sciences, 10115 Berlin, Germany.
authors.forename: Falk
authors.initials: F
authors.lastname: Mersmann
authors.affiliation: Technische Universität Berlin, Department of Medical Technology, 10587 Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Tettke
authors.affiliation: Technische Universität Berlin, Department of Medical Technology, 10587 Berlin, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Kraft
authors.affiliation: Humboldt-Universität zu Berlin, Department of Training and Movement Sciences, 10115 Berlin, Germany a.arampatzis@hu-berlin.de.
authors.forename: Adamantios
authors.initials: A
authors.lastname: Arampatzis
mesh_terms: D000125:Achilles Tendon / Q000033:anatomy & histology* / Q000502:physiology*; D000222:Adaptation, Physiological; D000328:Adult; D001696:Biomechanical Phenomena; D055119:Elastic Modulus; D015444:Exercise / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D013314:Stress, Mechanical
keywords: Exercise; Load; MRI; Tendon adaptation; Tendon hypertrophy; Tendon training