Feeling Perspired

Note: Dr. Tim Noakes has published a book entitled Waterlogged: The Serious Problem of Overhydration in Endurance Sports that sets out to debunk some myths about hydration and exercise.  Although I have not yet read this book, both the  reviews and introduction suggest that he takes a long, hard look at hydration needs and the associated sports drink industry.  Since I cant' really agree or disagree with something I haven't yet read, I can only relate my experience with heat, sweat, and hydration.  This post isn't focused on hydration and sports drinks,  but more on how hot weather impacts my performance as a runner.   In my unscientific opinion, hydration is a component of staying cool, but not necessarily the most important.

With the temperatures in town settling in at about 100 degrees, I decided that it might be a good afternoon to try an acclimation run as well as to do a calculation of my sweat rate.  I also wanted to make some mental notes about running in the heat that might help me should I find myself in very hot weather during a race.  So, at 3:45 yesterday afternoon, I set off for an hour run in the sun.  
Calculating sweat loss is a simple enough process.  Essentially you measure your weight both before an after an hour long run, and then you take into account any additional fluids that you consumed during exercise.  From this you are able to determine the volume of fluid utilized during exercise.  The University of Arizona has posted a nice little worksheet that you can use for calculation if you are so inclined.
I wanted to analyze not just my sweat rate, but also gather some qualitative data about running in the heat.  Therefore, I chose to avoid any cooling strategies (other than wearing a hat) during the hour long run, which is something that I probably wouldn't recommend to anyone. It is an admittedly stupid thing to do, and could be potentially dangerous.  However, it did make my calculations much easier, and I believe it provided some useful insights (at least for me) about running in the heat.

Before Run Data

The chart to the right shows some basic information about my run, and what the conditions were like.  In addition to this information I tried to assess both my physical and mental disposition at approximately 10 minute intervals throughout the run.  By better understanding how the heat impacts me physically and psychologically, I can take steps to either delay and/ or minimize the negative effects.  At the end of each segment, I've also listed my perception of both physical and psychological impact (kind of like a rate of perceived exertion or RPE).  In this scale, a "1" represents little to know impact, whereas a "5" would indicate a serious, even dangerous effect.  These are presented in a chart later  in the post.  Here are my notes from the 65 minute run:
@ Ten Minutes:  Physically speaking, there's not much of an effect at this point.  It is noticeably hot outside and there's also a bit of a warm breeze.  My legs feel a bit sore from all of the training during the last couple of weeks, which would indicate that I need to take a rest. In terms of perspiration, my face feels just slightly damp, but I'm not fully sweating yet.  As I look at my watch and note that I have 50 more minutes to run, I feel confident and comfortable, and I'm not at all thirsty.
Perception of Physical Impact (1-5): 1
Perception of Psychological Impact (1-5): 1
@ Twenty Minutes: I'm coming to the top of a long hill at this point with the wind at my back.  At  this point I'm definitely sweaty, and I can start to feel some sweat collecting on my forehead,nose, and chin, and it's beginning to drip off of my face.  I'm not really thirsty at this point, but I can tell that I will be thirsty soon.  There's just a slight dryness in my mouth and throat.  Mentally speaking, the heat hasn't really hit me at this point.  I'm more preoccupied with thinking about the route I'm going to follow to try and get back home right around one hour's time (perhaps something I should have thought about before I started running).
Perception of Physical Impact (1-5): 2
Perception of Psychological Impact (1-5): 1.5
@ Thirty Minutes:  I'm still sweating, but I've turned back into the warm wind, and the sweat seems to evaporate off of me without any kind of cooling effect.  Although I ate lunch over three hours ago, I'm feeling a slight twinge of nausea.  I didn't bring my HR monitor, but my heart rate seems to be a little higher, and if I push the pace at all, my breathing becomes more difficult. I feel slightly more thirsty, but I still have the sensation that I'll be okay a little longer.  Mentally, the run in the heat is starting to feel a little tougher.  I'm still trying to figure out my route (I'll decide on an out-and-back in another couple of minutes).  I try thinking about cool things, but this doesn't seem to help me get past the fact that it's hot!
Perception of Physical Impact (1-5):3.5
Perception of Psychological Impact (1-5): 3

Sample of heart rate under similar conditions (Avg Pace: 9:54/mile)

Sample of heart rate under cooler conditions (Avg. Pace: 7:52/mile)

@ Forty Minutes:  Heading back in the direction that I originally ran, I notice that I can hear my heart pounding in my ears, and so I dial back the pace a little bit.  I was hoping to do a negative split so that I could get back closer to an hour, but this no longer seems like a good idea.  I'm somewhat thirsty at this point, and my mouth and throat are starting to dry out.  Perspiration seems about the same as I'm running into the wind a little more again.  Closer to fifty minutes, I notice that my hands are starting to feel a little swollen, especially my fingers. Mentally, I'm just trying not to think about it.  When I look at my watch, I do try and tell myself that there are just a few minutes left.
Perception of Physical Impact (1-5): 4
Perception of Psychological Impact (1-5):3
@ Fifty Minutes: The biggest physical change at this point is that I'm feeling genuinely thirsty.  My mouth and throat are very dry, and my tongue feels thick in my mouth.  The wind seems to be pulling the sweat off of my body, so there's not much change there.  The nausea that I had experienced around thirty minutes is also back to some degree.  My state of mind has deteriorated as well.  About the only thing I can do at this point is tell myself that it's just a few more minutes.  It is very hard to pay attention to my pace or really to concentrate on anything for more than a few seconds at a time.  This isn't the hottest I've ever felt while running, but I know if I stayed out here much over an hour, I would find myself in some serious trouble.
Perception of Physical Impact (1-5): 4
Perception of Psychological Impact (1-5): 4
@ One Hour: I'm close to being finished at this point, and I consider walking the rest of the way, but I know that will only keep me outside longer.  If I had to guess my heart rate is in the mid to upper 150's, although my pace is only about a 10 minute mile.  In normal conditions, I would be running at a rate closer to 8:00-8:30/ mile.  I don't really notice much else in terms of how I feel physically, but I'm not really thinking about this at all.   I'm within a half mile of home, and that makes me feel somewhat better.  After five more minutes of running, I turn onto our street and reach the house.  The sprinklers are running and it's tempting to go lay down in the middle of the lawn, but I've still got to weigh myself.  I go inside and step on the scale.  After weighing in, I strip down and take a cold shower.  Melisa brings me a bottle of ice water to drink.
Perception of Physical Impact (1-5): 4
Perception of Psychological Impact (1-5): 4

Post Run Data

 The final data from my run is listed to the left.  In all honesty, I was really surprised that I'd lost so much sweat during an hour of exercise.  62 ounces is a significant amount (like a two-liter bottle!) and only emphasizes the importance of staying cool while exercising.  Fluid replacement is important, but other measures to keep cool like pouring water on your head, sponges, ice in your hat, etc. seem like they may have a significant impact.  Additionally, the qualitative data that I collected suggests that the psychological impact of running in the heat is also an important factor.  In the space of about 35-40 minutes, I went from full confidence, to being barely able to concentrate. I may not be the toughest person mentally, but I'm not exactly a wimp about things either.  Like many endurance athletes, the mental aspect of pushing through adversity over an extended time, is part of what draws me to endurance sports.

1= Negligible Impact, 2=Minor impact, 3= Moderate impact, 4= Significant impact, 5= Severe impact

A lot of the articles I read in preparation for this post suggest that one should conduct the sweat test in varying conditions so as to understand sweat rates at different temperatures, exertions, etc.  and that is something that I may try later on in the fall and the winter when conditions are different. For this experiment, here are the things that I learned about running in the heat:

• I sweat at a much greater rate than I would have imagined. I really expected that I might lose a pound, maybe two at most.  The fact that I lost approximately four pounds is staggering.  I don't think I'll ever look at a two-liter bottle of soda in the same way (a two liter bottle is nearly the equivalent of what I lost).
• Thinking about how hot it is while running only makes it worse.  At the same time, thinking of something cool, also makes the heat seem worse.  It's better to try and concentrate on something entirely different (e.g.- winning at Kona, Pizza toppings, top 10 favorite running songs, jumping into an icy, brisk mountain stream after drinking an ice cold beer).
• Heat has a major impact on both physical and psychological performance and these can deteriorate rapidly (consider that my perception declined from minor to moderate to significant in only 30/40 minutes time). My ability to concentrate was significantly impaired and under race conditions, would likely have a big impact on overall performance.
• Proactive and preventative measures when exercising, and especially racing in hot weather is essential.

  Today, I'm taking a break from training and considering the forecast is for a high of 102 degrees, this is a good thing.  If you are out today, I wish you the best of luck, and speaking both figuratively and literally, Stay Cool!