Eccentric

Eccentric exercise

Quantum mechanics

Plantar flexion

Engineering

Tendon

Biomechanics

Human physiology

Ankle

Isometric exercise

Muscle damage

Eccentric training

Achilles tendon

Strain (injury)

Mechanical engineering

Physics

Anatomy

Triceps surae muscle

Physical therapy

Internal medicine

Sports medicine

Structural engineering

Medicine

Physical medicine and rehabilitation

Tendinopathy

European Journal of Applied Physiology

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.

Effects of high loading by eccentric triceps surae training on Achilles tendon properties in humans