Originally Posted by
landdnl
Interesting article. So when you start a strenuous exercise, blood flow increases to the brain, accounting for 50% of the body's heat loss, but then demands from other parts of the body, muscles, skin, reduce the flow to the head. The 70 to 75% heat loss adage is attributed to the chimney effect from the clothing going up to the shoulders, neck, and head. Not internal heat loss. So I should have said that 70 to 75% heat loss occurs around the head, neck, and shoulder area.
No, re-read the article, the increased heat loss only occurs in the beginning of exercise, "
When you begin to exercise you increase the blood flow to the brain and increase the percentage of heat loss through the head to about 50% of total body heat loss. But as the person continues to exercise, the muscles demand more oxygen which increases blood flow. To ensure thermoregulation and maintain normal core temperature (exercises increases body heat), the skin vasodilates which increases blood flow to the skin to cool the blood. The net result is a decrease in the total blood flow to the brain and a decrease in percentage of total body heat lost through the head to about 10%. Once sweating begins, the percent lost through the scalp returns to 7%. Research at the Army Research in Environmental Medicine labs showed that there was a temporary increase in heat loss through the scalp that returned to the baseline of 7% as the subjects continued to exercise."