Very strange symptoms, cannot figure them out...?

Question

In gym class, I have a friend who, after working out, running etc. is hot and sweaty - except for his forearms. They turn a dark, bruised purple and they are very cold to the touch (imagine what a sweaty glass of a cold drink would feel like). If I press my finger lightly on his arm, his skin turns a bright yellowish color.

What exactly is causing this???

Answer 1

This is caused by a reflex that changes blood flow when the body starts heating up from exercise. The mechanism is part of complex circulatory changes in skin that occur in response to temperature changes or exercise. When someone starts to exercise (before they are warmed up), blood flow starts increasing almost instantly to the muscles that are being used. Since there is a limited volume of blood in the body, the extra blood has to come from somewhere, so flow is reduced in parts of the body that aren't being used at the same rate. Because internal organs need a more constant blood supply than skin or muscle, the only tissues available to rapidly supply extra blood are the limbs and skin.

If you are a runner, the blood flow (and oxygen supply) to the forearm and skin is likely to drop when running, which causes the skin to appear purple. When you press on the skin, it appears white or yellow because there is no blood in capillaries.

All of this is normal if it only happens during or following exercise.