In a crossover trial nine volunteers received treatment of the Achilles tendon with 10 minutes of either acupuncture or a heat pack. During needle insertion, the blood volume and oxygen saturation of the tendon increased significantly compared to pre-treatment levels, and these values remained high throughout the 30-minute recovery period. During heat treatment, the blood volume and oxygen saturation of the tendon also increased significantly. Although the increased blood volume was not maintained after removal of the heat pack, oxygen saturation remained significantly elevated throughout the recovery period. The long-lasting increase in blood supply to the tendon, seen especially with acupuncture, may explain how these treatments exert therapeutic effects on injured tendons.

Effects of acupuncture and heating on blood volume and oxygen saturation of human Achilles tendon in vivo. Eur J Appl Physiol. 2010 Feb 6