The Achilles tendon doesn’t get even blood flow along its full length. A section roughly 2 to 6 centimeters above where it attaches to the heel bone gets noticeably less blood supply than the rest of the tendon — this is the “watershed” zone, sitting between two blood supplies that don’t fully overlap.
This same zone is where most chronic Achilles tendinosis and most Achilles ruptures happen. That overlap is thought to be more than a coincidence: less blood flow likely limits the tendon’s ability to repair everyday microdamage, leaving this section more vulnerable over time.
This explains where and why Achilles injuries concentrate and heal slowly — it is not itself a treatment. It does not mean a circulation-boosting or injectable product changes outcomes here. The loading-based rehab behind the Alfredson protocol remains the approach with actual evidence behind it, regardless of the vascular explanation.