Introduction An inadequate blood supply plays an important role in the development of injuries. It is known that physical activity has an influence on the blood flow of a tendon. However, it remains unclear which type of activity leads to the highest increase in blood flow. Therefore, the aim was to compare the immediate effect of 5 different physical activities (running, stretching, plyometrics, eccentric heel drops, T-test) on the blood flow of the Achilles tendon.

Methods Thirty healthy subjects performed each of the 5 activities spread over a period of 3 weeks. Blood flow, saturation and haemoglobin were measured biateral before and after each activity. 12 well-defined tendon points were summarised into 4 regions: insertion, distal midportion, proximal midportion and musculotendinous junction. Changes were statistically analysed using a mixed model analysis.

Results At the insertion, running is the only activity which has an immediate effect on the Achilles blood flow (p < 0.001). This significant increase in blood flow due to running is also found in the distal midportion (p < 0.001), the proximal midportion (p = 0.001) and the musculotendinous junction (p = 0.019).

When compared to the other 4 physical activities, running differs significantly, especially at the insertional region and at the distal midportion. The P-values range from 0.000 to 0.016. In the proximal midportion, running also shows the highest increase and differs significantly from heel drops, stretching and T-test. At the musculotendon unit, only 2 significant P-values are seen; between running and stretching and between running and heel drops. The results of saturation mainly follow those of blood flow whereas the results of haemoglobin are unclear.

Discussion The results demonstrate that running implicates the highest increase in blood flow of the Achilles tendon and this throughout the four regions of the Achilles tendon. The present results are in agreement with the observation of a decrease in blood flow after eccentric training and stretching (Knobloch et al., 2007). It is reasonable to assume that due to a tendon stretch the blood vessels within the tendon stretch and become thinner, which results in a slower flow. The higher increase due to running might be explained by the exercising time. The duration of tuck jumps and T-test may not have been sufficient to induce a vasodilation to increase tendon blood flow (Malliaras et al., 2012).

In conclusion, if one wants to increase the blood flow of a tendon, it can be recommended to perform physical activities, in which the tendon is loaded cyclically.

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