Background The influence of warm-up exercises on the muscle properties has already been investigated before. Strikingly, it still remains unclear which warm-up exercises should be performed in order to properly prepare the Achilles tendon in withstanding high-forces during sport participation.

Objective To investigate the acute effect of frequently used warm-up exercises on the Achilles tendon blood flow and stiffness.

Design A within-subject repeated-measure design.

Setting Knowledge about which exercises are suitable to prepare the athlete’s Achilles tendon in withstanding high amounts of loading during sport activities could help sport physicians and physiotherapists when recommending warm-up exercises that are able to improve sport performance while reducing the injury susceptibility. This study was conducted at the department of Rehabilitation Sciences at Ghent University.

Participants All 40 participants performed at least 1 hour of weekly sports participation and were excluded from this study if they had a history of lower extremity injuries within the previous year.

Assessment Achilles tendon blood flow and stiffness measurements were obtained before and immediately after four different warm-up exercises: running, plyometrics, eccentric heel drops and static stretching. The effect of these warm-up exercises and possible covariates on the Achilles tendon blood flow and stiffness was investigated with linear mixed models.

Main Outcome Measurements Achilles tendon blood flow and stiffness.

Results The results showed a significant increase in Achilles tendon blood flow and stiffness after 10 minutes of running (p< 0.001 and p< 0.001) and plyometrics (p< 0.001 and p= 0.039). Static stretching and eccentric exercises elicited no significant changes.

Conclusions It could be suggested that warm-up exercises should be intensive enough in order to properly prepare the Achilles tendon for subsequent sport activities. When looking at Achilles tendon blood flow and stiffness, we advise the incorporation of highly intensive exercises such as running and plyometrics within warm-up programs.