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±4.1cm; body mass: 78.4±6.3kg) 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 (10×25s plantarflexion contractions at 50% MVIC), and then at either 15, 30, 60, 90 or 120min 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<0.001). There were no significant differences in free AT longitudinal or transverse strains at 60min relative to 0min post-conditioning, or between pre-conditioning strains and strains measured at 2h (p>0.05).

Conclusions: The free AT undergoes a creep response during conditioning which is recoverable within 2h 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 0-60min post-conditioning.