Why is your stomach cold after a hard workout?

Answer 1

If you have not been working your abdominal muscles, they will not receive as much blood as the working muscles. More commonly, it is the evaporating sweat from your midsection that makes it feel colder.

Answer 2

If you are human, you have body fat. When you work out, your muscles are working very hard, but your fat does no work. While the rest of your insides warm up, your fat gets cold because of your sweat and air passing by it.

If you don't want a cold stomach, lose the fat.