Mechanical loading of the Achilles tendon during isolated eccentric contractions induces
immediate changes in its structural properties. However, it is not known whether the
loading speed and intensity has any impact on these changes. Therefore, this study aims
to investigate the influence of loading speed and intensity during eccentric heel drop
exercises on the immediate changes in Achilles tendon thickness and stiffness in healthy
controls.
Each participant will perform eccentric heel-drops on their dominant leg with and a fully
extended knee, and with additional 20% body weight (added via a weighted backpack).
Participants will stand with the forefoot of the tested limb on the edge of a step, with
the ankle maximally plantar flexed and with body weight centred on this limb. Eccentric
loading occurs when the participant lowers the heel to a predetermined angle and speed
(depending on the type of intensity and speed cfr infra). In order to return to baseline,
the body mass will therefore be shifted to the non-dominant leg to raise the body. Visual
feedback (monitor) will be in front of the subjects and the exercise parameters (velocity
and ankle angle) will be guided by software guidelines (Ultium Motion).
Three protocols will be compared that differ in execution speed (namely a fast protocol;
1 Hz: 1 second per repetition versus a slow protocol; 0.33 Hz: 3 seconds per repetition)
and loading intensity (namely heavy; exercise into maximal dorsiflexion versus light;
exercise into neutral ankle position).
Protocol 1 (=Heavy x Slow): subjects perform eccentric heel drops from a maximal
plantarflexion position to a maximal dorsiflexion position at a speed of 0.33 Hz, i.e. 3
seconds per movement cycle.
Protocol 2 (=Heavy x Fast): subjects perform eccentric heel drops from a maximal
plantarflexion position to a maximal dorsiflexion position at a speed of 3 Hz, i.e. 1
seconds per movement cycle.
Protocol 3 (=Light x Slow): subjects perform eccentric heel drops from a maximal
plantarflexion position to a neutral ankle position at a speed of 0.33 Hz, i.e. 3 seconds
per movement cycle.
Participants will perform one exercise protocol per session, in a random order, and the
interval between each session is one week. Six sets will be performed per session, with
one minute of rest between each set. In order to ensure that the Achilles tendon's time
under tension is the same for each protocol (180 seconds), 30 repetitions will performed
per set for the fast protocol and 10 repetitions for the slow protocol. The approximate
duration of each intervention will be 15 minutes. Before and immediately after each
protocol, the structural properties of the Achilles tendon, 20 mm proximal to the
calcaneal posterosuperior border, will be assessed. These properties include tendon
thickness (anteroposterior diameter (mm), cross-sectional arae (mm2)), and tendon
stiffness by shear wave elastography (m/s).