Recovery of human Achilles tendon three-dimensional deformation following conditioning

Objectives: The tendon conditioning effect is transient, but the time course of recovery from conditioning is not known. This study examined the time-course recovery of three-dimensional (3D) Achilles tendon (AT) deformation immediately following a standardised AT conditioning protocol. Design: Randomised crossover. Methods: Ten healthy male adults (age: 24 ± 5 years; height: 175.8 ± 4.1 cm; body mass: 78.4 ± 6.3 kg) attended the laboratory on 6 occasions. ATs were scanned using freehand 3D ultrasound during a 50% maximal voluntary isometric contraction (MVIC) of the plantarflexors immediately prior to and following the conditioning protocol (10 × 25 s plantarflexion contractions at 50% MVIC), and then at either 15, 30, 60, 90 or 120 min post-conditioning, randomised by session. Results: Free AT longitudinal strain was significantly increased from 3.13 ± 0.19% pre-conditioning to 7.49 ± 0.20% immediately post-conditioning and was accompanied by a corresponding reduction in free AT transverse strain from −5.35 ± 0.48% to −10.16 ± 0.49% (p 0.05). Conclusions: The free AT undergoes a creep response during conditioning which is recoverable within 2 h following conditioning. Recovery from conditioning has the potential to be a source of error during in vivo measurement of AT mechanical properties. The time window in which the free AT longitudinal and transverse strains could be achieved without a large confounding effect of creep recovery is 0–60 min post-conditioning