Hydration Challenge Update #1: What’s My Sweat Rate?

I chose to focus on hydration as my first challenge in 2021. My goal is to drink 85oz fluids daily and try to get at least 20oz water as part of my fluids each day. I have been tracking what I drink in my planner and at the end of the day I add up my totals, divide that by my goal of 85oz and then give myself a percentage of goal met. I haven’t quite met 100% of my goal, but I have had some really good days. I am also noticing that by paying attention to my hydration habits I am able to honor my thirst better. If you’re joining me in this challenge, how are you doing? Let me know in the comments on my Facebook or here on my blog!

My motivation for choosing this as my first challenge of 2021 was from reading Nancy Clark’s Food Guide for Marathoners (my plan is actually to read the whole book during this training cycle and share what I have learned with all of you through my challenges). I knew I wanted to start by focusing on something that I could add to my regimen versus something restrictive, so I flipped right to the chapter on Water & Sports Drinks. One of the first statements that stuck out to me in the chapter was a history lesson: “In 1953, running regulations stated that marathoners could take water only after 9.3 miles.” What!? Now I know I’m not drinking enough when I run races, but I definitely don’t wait until over 9.3 miles to have my first sip!

Nancy’s book continues by stating that while dehydration is a big concern of many marathoners, overhydration can cause problems, too – so how do you know how much to drink? As I mentioned in my previous post, honoring your thirst and paying attention to your bathroom habits can be helpful. If you’re like me and struggle with remembering to drink or knowing when you are thirsty, figuring out your sweat rate can be extremely helpful. So last week, I did just that!

I am not normally pro weighing oneself, especially not frequently, but when it comes to calculating your sweat rate and monitoring your hydration status as a runner, stepping on the scale can give you some great insight. Here’s how to calculate your sweat rate, and how I figured out my own:

• Weigh yourself (without clothes) before and after a 60 minute workout. Don’t drink any fluids during this workout. Make it a workout of average effort. (I shoveled snow and went for a walk the day I figured out my sweat rate.)
• Figure out the difference in your weight from before and after the 60 minute workout.
• Remember the phrase, “A pint a pound the world around!” My very first nutrition professor taught us that and I will never forget it. A pint of fluid weighs approximately 1 pound. So if you lose 1 pound after doing a 60 minute workout, that means you are losing about 1 pint of fluid every hour. Your sweat rate is 16oz per hour, and Nancy Clark’s book recommends trying to drink that amount during workouts to prevent too much fluid loss – 16oz per hour.
• If it is difficult for you to do a 60 minute workout, you could also do a 30 minute workout and just double your weight difference to figure out your sweat rate.

I put this sweat rate to the test on my run on Saturday. I was running 7 miles, which I knew would take me about 90 minutes to complete. Before I ran, I weighed myself. I took my 16oz handheld water bottle with me filled with Nuun Endurance formula. I also practiced fueling a little differently, which I will talk about in a different blog post. I took drinks every mile at least, and every time I felt thirsty. I did not end up drinking all 16oz (I’m guessing I drank about 12oz) but I think I drank more than I normally would during a training run. When I was finished, I weighed myself again.

I only lost 0.6lbs from that run. Per Nancy Clark’s Food Guide for Marathoners the goal is to lose less than 2% of your body weight during a run to prevent dehydration. Mine was only 0.35%, so even though I didn’t drink as much as my sweat rate indicates I should, it was adequate for me. I did notice that my stomach felt a little sloshier than normal during the run. This is why it is important to experiment with your fueling and hydration during your training runs – what works for one person won’t always be what is best for you! You don’t want to be trying anything new on race day. By then you want to have a confident, solid plan for your fueling and hydration.

Stay tuned for my next update: I’ll let you know how I am doing with meeting my goals and will discuss different sources of hydration!

References:

Nancy Clark’s Food Guide for Marathoners, 5th edition.