Let’s talk about sweat

Since we’re all about bodily fluids here today on the RunRunLive Podcast I wanted to talk a bit about sweat.  You may think sweat is fairly straight forward, but, all these things that happen in our bodies are complex dances of many influences.

I would imagine all of you are familiar with sweat.  When you exercise in the heat you sweat.  Your body moves blood to the skin and you sweat water and salts. That sweat evaporates absorbing 500 Kcals per mole, which, trust me is an astoundingly amount of energy in the form of heat.  Sweating is very efficient.

You know you need to take in fluids and salt.  But how much?  When?

In the beginning of the running boom the advice, as cringeworthy as it was, was to drink a lot of water and sports drink.  “Don’t wait until you’re thirsty!  Drink!  Keep on top of your hydration!  And get plenty of electrolytes! Your body needs electrolytes! Plants, I’ve been told, love electrolytes!”

Yeah you do have to work around fluid and salts loss during long workouts but it’s not as simple as you were probably told.

Electrolytes are more than just salt.  They are a mix of sodium, chloride, potassium and other trace elements that help your cells function.  One very important thing that electrolytes facilitate is the transmission of fluids and fuel across cell membranes.  The difference between the inside of the cell and the outside of the cell will cause fluids and electrolytes to be pulled in one direction or the other.

That’s why if you take too much of any one thing, like water, it screws up this transmission across cell membranes, the osmosis, which is both a chemical and electrical process.  The break down of the electrical processes at the cellular level due to imbalances can cause cramping.

Your body does a good job with keeping these things in line but can get overwhelmed when you’re out for a long time and not fueling well.

Contrary to a lot of old advice, what your fueling strategy is attempting to do is to maintain this balance as well as possible over the course of a long outing.

How much do you sweat?  This, it turns out, is a very personal question.  Sweat rates are effected by many factors. You, yes you, have your own personal sweat rate, that’s your baseline.  And you, yes you, will react to different influences differently than the athlete next to you.

I always thought I was a heavy sweater.  But, I’m probably right in the middel of the normal range.  How do I know this?  Because I have measured my sweat rate. I have a base line.  The average person sweats between 25 – 50 ounces an hour during exercise.  That’s like one or two Bike bottles.

The highest recorded sweat rates are up close to 4 liters and hour – that’s close to a gallon – Like a big milk jug full of sweat.  There are a lot of things that influence your sweat rate.  Obviously, the temperature, the humidity and the intensity of the exercise will vary your sweat rate greatly.

Here’s how you check your sweat rate. Weigh yourself, naked of course.  Get on the treadmill, but not naked, get dressed first.  Workout for an hour at your normal low zone 3 casual pace.  Get out of those sweaty clothes.  Weigh yourself again.  Subtract anything you drank during that hour or eliminated during that hour.  That’s your baseline, room-temperature, average intensity sweat rate. For me that is going to be about 20 ounces.  If you want to get some other data points do the same test on a hot day outside, or a cold day.

You will get a good idea of what your sweat rate is.  Now you can use that information to figure out what you need to fuel over the course of a workout or event.

This is also going to vary with intensity and across sports if you’re a multisport athlete.

One thing to remember is that you don’t have to be perfect.  Your body is good enough at this business to be able to still operate a bit dehydrated or even overhydrated.  So, don’t sweat the details too much.  (Couldn’t resist).  If you try to take in too much that can lead to nausea and other problems.  Many times, towards the end of a race, I’ll ditch my bottle because I know it won’t make a difference in the last 30-40 minutes.

On a hot day my sweat rate is going to double or more.  Most runs I can carry my single 24 oz bottle and be good for an hour and a half.  In hot weather that’s not enough.  At higher intensities that’s not enough.  I aim to get 20+ ounces in an hour.  Even at that rate I will be 6-8 pounds lighter at the end of a raced marathon.  That’s a gallon light at the end of a race.

The bad news is that, just like the sweat rate, your ability to absorb fluids and nutrients is also specific to you, yes you.  Some athletes can’t absorb enough fluids to keep up.  Some can cram fluids and fuel and have no problem.  It’s something you can practice and experiment with.

You have to be mindful of your sweat rate going into a long work out.  You have to experiment with different forms of fluids and nutrition.

I have found that an electrolyte supplement every 10K or so in a race makes a difference on my ability to race when I get deep into the race.  In hot weather I might double up on that and take 2 electrolyte supplements an hour.  That seems to stave off any cramping or crashing late in a hot race.

For fluids I always have raced with a bottle in one hand.  This is typically a 20 or 24ounce bottle.  When I start the race I’ll have some sort of fuel in the bottle and I’ll refill it as I go depending on how I feel.  I’ve raced successfully on a lot of different fuels, including plain old Gatorade in the old days.  It’s really personal preference.

Which brings us to the biggest advice I have for you.  Figure it out.  Don’t let someone else, especially a vendor, tell you what your fueling and hydration strategy should be.  Do a little bit of research.  Know your baselines.  Then experiment around those baselines.

There’s two big reasons I’m able to race well on a variety of fuels.  First, my body and how it reacts is specific to me and I’ve had years to observe how it reacts to what.  Second, I’ve practiced all this fueling throughout my training campaigns.  Your body can be trained.  Experiment.  Make mistakes.  See what happens.

Stay safe and stay hydrated my friends.