title: Method and strain rate dependence of Achilles tendon stiffness.
abstract: Tendon stiffness is calculated by dividing changes in tendon force by tendon elongation. For this purpose, participants are commonly asked to perform a maximal muscle contraction ("active" method). Alternatively tendon elongation can be achieved by means of a passive joint rotation ("passive" method). The purpose of this study was to compare Achilles tendon stiffness obtained from both methods across different tendon strain rates. Twenty adults performed a series of ramped maximum isometric plantarflexions of different durations. Passive ankle rotations of different angular velocities were also performed. Achilles tendon stiffness was obtained from a combination of motion analysis, isokinetic dynamometry and ultrasonography and compared across methods at three strain rates. At all strain rates, tendon stiffness obtained from the active method was 6% greater compared to the passive method. In spite of this systematic bias, there was good agreement between the methods. Intraclass correlation coefficients were greater than 0.98, and more than 95% of data points fell into the 95% confidence intervals. This agreement will be acceptable in many research contexts. We also found a linear increase in tendon stiffness with increasing strain rate, which must be taken into consideration when interpreting or reporting tendon stiffness.
authors: Centre for Sports Medicine and Human Performance, Brunel University, London, UK.
authors: Nicola
authors: N
authors: Theis
authors: Amir A
authors: AA
authors: Mohagheghi
authors: Thomas
authors: T
authors: Korff
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D000843:Ankle Joint / Q000502:physiology*; D004548:Elasticity / Q000502:physiology; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009068:Movement / Q000502:physiology; D053581:Muscle Strength Dynamometer; D012399:Rotation; D019415:Torque; D014463:Ultrasonography