The last discussion on hydration was referring to the variety of ways the body will loose water in a 24 hour period while not exercising. Recall that 600 ml of water was lost through the skin by a process called insensible loss. This is essentially water being evaporated from the skin without our sensing this action. This equates to about 20% of our body water loss, the majority is through urination.
However, this all changes significantly with exercising. The entire reason for sweating is to rid the body of heat due to the increased rate of muscle contraction (metabolism). If we can not get rid of this heat, we will literally burn up from the inside! So, in order to prevent this from occurring, the body brings more blood to the skin surface attempting to release the heat to the outside. As the skin gets hotter, more heat escapes. A practical example of this is when placing your hand on someone’s forehead to check for a fever.
This process alone would not be able to rid the increase heat production. Placing water on the skin surface will insure a much faster way to lose the heat. By acting as a sponge to “absorb” the heat (energy), causes the water molecules to move faster and faster until it is able to break free from the surface in the form of steam. Yup, we are actually boiling water!
How fast the evaporation occurs is strongly influenced by environmental conditions. The chart below shows how much water is lost while running in hot and humid conditions compared to cool and dry. The overall change is about 4 times more water loss in hot and humid conditions. Mother Nature plays a bit of a prank on us. She tricks us to sweat more because the environmental conditions are not good for quickly cooling down our body. Our body tries to cool down faster by sweating more. This helps a bit, but we are sacrificing more water resulting in faster dehydration and decreased performance.
The chart below is average sweating rates per hour of activity.
Remember that 1 liter is equal to 1 lbs. For example, if you were to play competitive tennis in the summer, you could lose as much as 2 lbs per hour; even more in hot and humid conditions.
To set up a chiropractic or massage office visit: Online scheduling