Heat, infrared and the body's response
Capillary development / angiogenesis
Angiogenesis is the growth of new blood vessels, usually capillaries sprouting from existing ones under signals such as vascular endothelial growth factor. It is how a tissue increases its own blood supply over weeks, as it does with exercise training.
Also called angiogenesis, capillary development, neovascularisation
Three related processes are often confused:
- Vasculogenesis — blood vessels forming from scratch out of precursor cells, mainly in the embryo.
- Angiogenesis — new capillaries sprouting from vessels that already exist. Endothelial cells are activated, usually by vascular endothelial growth factor (VEGF) released by tissue short of oxygen, degrade the surrounding matrix, migrate, and form a new tube.
- Arteriogenesis — existing small collateral vessels enlarging in response to shear stress.
Timescale is the point. Angiogenesis is a structural remodelling process measured in days and weeks, driven by a repeated stimulus. Endurance training reliably increases capillary density in trained muscle over weeks. That is what a genuine angiogenic effect looks like, and it is very different from the immediate widening of existing vessels during a hot session, which is vasodilation and reverses as you cool down.
Applied to saunas. Repeated passive heating raises blood flow and shear stress, and how that relates to vascular adaptation is an active research question in exercise physiology.
Why it matters here
It is the difference between the temporary flush of a hot session and a lasting change in a tissue's blood supply. The two are often described in similar words and they are not the same thing.