Quote (mizure @ Oct 25 2010 09:08am)
your muscles get pumped with blood when working out.
your veins enlarge because It is easier for them to carry blood around
Since you need it fast and the heart usually beats faster
If you had thin veins then your blood pressure woud go through the roof.
Sorry, but wrong physiology
Veins don't enlarge during intense work outs, as a matter of fact, they venoconstrict (becomes narrower).
If they had enlarged then you'll get a decreased blood pressure, hence decreased blood flow, therefore less blood is pumped back into the heart.
Bulging of the vein is caused by a process known as "filtration" and this is where plasma is forced out of the vessel walls into muscles, ultimately causing muscle swelling.
Muscle swelling results in surrounding veins to be pushed against your skin, that's why you see them... it's a normal process so don't worry about it

Hope this helped!
This post was edited by hwd-2 on Oct 24 2010 04:03pm