Understanding Sweat

I sweat when I run.  A lot.  Often as much, or more, than the men I sometimes run with.  I've learned not to wear gray shorts on a warm day, and I struggle to drink enough to keep me hydrated when I run during the summer.  But what does all this sweat mean?  Am I healthy?  Freakish? Efficient at cooling?  I was tired of not knowing the answers to these questions, so I decided to do a little digging and get to the bottom of this sweaty situation.

First of all, sweating is good.  The evaporation of sweat from our bodies is our defense against heat stress, which will lead to cardiovascular issues and all kinds of other nasty problems if not controlled by a good sweat response.  But it is the evaporation, and not the act of sweating itself, that is important.  This is why people struggle on a humid day - the humidity reduces the evaporation level, which makes our mechanism for cooling less efficient.  We might sweat like crazy on a humid day, but still suffer from heat illness if the sweat can't do its job. 

Our fitness levels do affect our sweating.  As our fitness levels (as measured by VO2 max) increase, the onset of our sweat response occurs earlier.  Fit people have lower resting core temperatures, so our bodies will respond to an increase in temperature earlier than a person who is less fit.  Other factors in our sweat reponse include our hydration status (less water in the body = less sweat), our exercise intensity, environmental factors (like heat) and acclimatization.  Research has shown that people who live in warm climates have delayed sweat responses; their bodies will not begin producing sweat until their core temperatures are higher than what a person who does not live in a warm climate.

We can acclimate to warmer temperatures.  This typically takes about 5 days, and it is recommended that we spend time exercising in the heat and making sure that we sweat profusely.  For more information on acclimatizing, check out this article. 

So we know that sweating is good, and that the earlier we sweat, the more we fit we really are.  But what about sweat volume?  Is more better?  Unfortunately, that doesn't seem to be the case.  Sweat rates look to be fairly individual, and what you sweat out is the same way.  Some people are "salty runners", leaving a crusty, white residue on their skin as the sweat evaporates (that's me).  And because a heavy volume ends up costing you valuable hydration, big sweaters have more issues with keeping fluid and electrolyte levels in balance.   It would seem to be to your advantage to sweat efficiently - just enough to keep you cooled, but not enough to wipe out your reserves.  And it's something we don't really seem to be able to control.

So what is a big sweater to do?  Awareness appears to be the key.  A good way to find out how much you sweat is to perform the following test:  Weigh yourself before heading out on a 1 hour run.  Do not take in any fluids after the weigh-in or during the run.  When you get back, weigh yourself again, and find the difference in weight.  Divide that number by 2.1 - this is the number of quarts you need to drink to replace the lost fluid.   Once you know that you sweat a lot, you can do all you can to keep hydrated and to replace lost electrolytes with drinks like Nuun or GU2O.  For more information on hydration, Runners World has some great articles.

And so now I know.  I'm healthy, but I also sweat alot without any extra benefit.  Now if I can just remember to wear the dark shorts . . .