CALCULATE YOUR SWEAT RATE
Calculating your sweat rate can be an extremely useful (and often shocking) training tool. A key component of a successful training program is being CONSISTENT from workout to workout. Consistency has far less to do with motivation or ability and far more to do with little habits that help us prepare for and recover from those workouts.
Hydration is one of those critical habits, as something as small as a 2% decrease in bodyweight due to dehydration can result in a massive decrease in performance.
TOOLS NEEDED:
Accurate Scale
Towel
Optional - bike trainer or treadmill for ease
HOW TO CALCULATE
Calculating your sweat rate isn’t actually all that complex.
Weigh yourself before training (but after going to the bathroom) in as little clothing as possible or depending on if you’re doing this in the comfort of your own home, no clothing at all for the highest accuracy. The reason being as you sweat, if your sweat comes out and just soaks into your clothes then it won’t show up as a “loss” if you have those same sweaty clothes on when you weigh yourself at the end. (Side note: don’t judge yourself for the number on the scale, it is far less important to performance than you might assume :) )
Train for an hour. This can really be doing anything, but if we are runners or triathletes we probably want to focus a bit on specificity.
Monitor any fluids consumed. Or better yet, try not to take any in. Of course, be safe about this but if you’re used to running for an hour without stopping for water then you should be fine. Doing this inside on a trainer or treadmill can help you monitor better if you need additional fluids.
Weigh yourself after training, again in little-to-no clothes and having dried yourself off really well.
Do some math. (WEIGHT BEFORE)-(WEIGHT AFTER)= FLUIDS LOST in LBS. Multiply pounds by 16oz and boom, you’ve got your 1 hour sweat rate. Most of us likely sweat around 28-32oz per hour but there is actually quite a wide range here.
Test both bike and run! Running is much more mechanically involved and usually associated with higher heart rates & sweat rates. It can be helpful to know the difference.
APPLICATION
Okay, now that you have your sweat rate, what do you do with it? This is actually where it gets a little more complicated because it isn’t necessarily a 1 out = 1 in ratio. In fact, there’s no “perfect” ratio. Instead, what we can focus on is making sure we’re staying above that 2% drop in dehydration by the end of our events and especially make sure we’re properly hydrated for workouts. We want to be close to our sweat rate, but it’s a pretty inexact science due the the variability in workout conditions, durations, and intensities.
For example: If I have a 1.5 hour indoor trainer ride scheduled, I’ll typically prepare 2x28oz bottles and try to get through 1 per hour and keep sipping on the second one afterwards so that I stay prepared for the next workout either later that day or the following morning.
For a second example: If I have a 30 minute easy run scheduled, that might be a fluid loss of 18 ounces (my sweat rate is pretty high), yet I wouldn’t actually bother bringing a water bottle on this run as it’s not very long or intense. I would simply try to have a bottle afterwards.
And for another example: In most cases, run sweat rate is higher BUT it is harder to drink a ton of fluids on the run. Bike sweat rate is usually lower but since you’re stable in the upper half of your body (hopefully!) then you can try to front-load your fluids and nutrition on the bike in a triathlon!
OTHER CONSIDERATIONS
Daily Hydration - We need water for more than just sport. Without diving into the specifics, most of us perform optimally with the simple formula of 1/2 your body weight (lbs) in fluid ounces + any fluids lost from sweat in exercise. Other sources of fluids CAN count but might not be as effective at hydrating us as water or electrolyte drink.
Weather/Conditions - If you did this outside on a normal day, or a day that resembles your normal racing conditions then do adjustments needed, but if you’re doing this inside on a treadmill or bike trainer it can be helpful to have a fan going. If you’re inside then you don’t have the cooling effect of air moving around you due to the stationary nature of the workout, which can skew the sweat rate high. You can also try this a few times to see how cooler/warmer temps might affect your sweat rate!
Intensity - Low intensity tends to be a lower sweat rate. Try to mimic your “race” effort or closer to it so that you get a more accurate measure for race fueling.
Calories & Electrolytes - The concentration here is what matters the most for both of these things. We could dive into great detail for both categories, but sweat contains sodium and as we move we burn/use calories!