Effects of high loading by eccentric triceps surae training on Achilles tendon properties in humans
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To document the magnitude and time course of human Achilles tendon adaptations (i.e. changes in tendon morphological and mechanical properties) during a 12-week high-load plantar flexion training program.
Ultrasound was used to determine Achilles tendon cross-sectional area (CSA), length and elongation as a function of plantar flexion torque during voluntary plantar flexion. Tendon force–elongation and stress–strain relationships were determined before the start of training (pre-training) and after 4 (post-4), 8 (post-8) and 12 (post-12) training weeks.
At the end of the training program, maximum isometric force had increased by 49% and tendon CSA by 17%, but tendon length, maximal tendon elongation and maximal strain were unchanged. Hence, tendon stiffness had increased by 82%, and so had Young’s modulus, by 86%. Significant changes were first detected at post-4 in stiffness (51% increase) and Young’s modulus (87% increase), and at post-8 in CSA (15% increase).
Achilles tendon material properties already improved after 4 weeks of high-load training: stiffness increased while CSA remained unchanged. Tendon hypertrophy (increased CSA) was observed after 8 training weeks and contributed to a further increase in Achilles tendon stiffness, but tendon stiffness increases were mostly caused by adaptations in tissue properties.
KeywordsHuman tendon stiffness Myotendinous junction Ultrasound Eccentric training
Analysis of variance
Evaluation before control period
Intraclass correlation coefficient
Maximal voluntary isometric contraction
After 12 high loading training weeks
After 4 high loading training weeks
After 8 high loading training weeks
After a 4-week control period
Slope of the force–elongation curve obtained from 50 to 100% of peak force of the weakest participant
Slope of the force–elongation curve obtained from 50 to 100% of maximal isometric voluntary force
Slope of the stress–strain curve obtained from 50 to 100% of peak force of the weakest participant
Slope of the stress–strain curve obtained from 50 to 100% of maximal isometric voluntary stress
The authors would like to acknowledge Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Programa Ciências Sem Fronteiras (CSF) and Financiadora de Estudos e Projetos (FINEP) from Brazil for financial support, and Amanda de Lima and Mayra Casa Nova for technical support.
Study conception and design: JMG, MAV, BMB, data acquisition: JMG, FJL. Analysis and interpretation of data: JMG, RRB, FJL, BMB, MFB, MAV. Drafting of manuscript: JMG, BMB, RRB, FJL, MFB, MAV. Critical revision: JMG, BMB, RRB, FJL, MFB, MAV.
Compliance with ethical standards
Conflict of interest
No conflicts of interest, financial or otherwise, are declared by the authors.
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