Dialing in Race Day Fueling with hDrop

The 2026 season brought a few changes for me, one of which being a new nutrition partner. The new partner’s products were significantly different than my previous, so I was basically re-building my race day fueling strategy from the ground up. This can often be a daunting task, but even for a seasoned veteran it is an opportunity to make sure you aren’t missing anything and not just going through the motions trying to do what you’ve always done. I’ve always been a believer that you have a nutrition specifically for the course, not just for the distance. Each course is going to present different demands which need to be addressed by your fueling. Thankfully, my first race of the season was Ironman New Zealand which is a fairly benign course in terms of weather and conditions so I was able to work to dial in my baseline nutrition strategy for an Ironman race leading into the event.

If you’ve followed the hDrop blog, you know that there was an article published recently discussing the Precision Hydration Pilocarpine Sweat Test (HERE). This test can serve as a great starting point (and indeed was the beginning of this process for myself as well). However, if you look through the recent article by Harris and collogues, you’ll also learn that you can just end your planning process there. Sweat rate and electrolyte concentrations change along with the current level of fitness,  intensity of exercise, environmental factors (heat and humidity), and even the sport we are doing. Your sweat rate while riding at 30mph will be different than when running at 10mph even if your HR is the same due to the airflow. This is where the hDrop tech becomes a vital tool to help you dial in your race day nutrition strategy.

Why is it so important to have a fueling strategy for the specific course you might ask. If you’ve been watching the sport progress the last 10 years, you have likely notice how much faster the times are getting across all distances. Obviously better gear is playing a role in this…but one of the most significant changes is nutrition technology. We once thought that roughly 80-100g of carb per hour was the maximum the body could absorb. Newer product developments have allowed us to throw that recommendation out the window. Carb availability in the body is a primary determining factor to maintaining your exercise intensity. In other words, provided ample blood sugar, you can maintain higher intensities for longer. But the higher intensity, the more heat we generate, the more sweat we lose, the more electrolytes we must replace. This is the math equation we must master for maximum performance. Each individual gut can only handle so much osmolity (the amount of particles in a concentration). So we need to find the right balance of Carb, electrolyte, and water to still allow optimizing our long performances without hindering our gastric emptying. Hotter and more humid races will lead to higher sweat rates. So we likely need higher electrolyte concentrations. This typically means we need to either increase our fluid intake or decrease our CHO intake slightly so we don’t make the osmolity concentrations too high and limit the ability for the gut to process what we are feeding it (no one wants to be the one running down the course puking your guts out as in front of the fans…although can be good for Instagram clicks!).
The assumptions I made for IMNZ in my prep were that it would be a moderate temp, light wind, and lower humidity day. Temps would start cool and grow throughout the day. A unique feature about racing in NZ is that there is a high sun load which means you’ll absorb a lot of heat from radiant energy making the run feel much hotter than temps would suggest. I trained for the race primarily in CO, so had plenty of indoor and cooler outdoor sessions, but was also able to bank a solid week of training in Florida with some warmer temps. Here are a few things I found particular interesting and important:

1. Regardless of the temps, my sweat tended to get more concentrated over the duration of the exercise. I was losing more salt per ounce of sweat in the later stages of exercise than the early stages. I needed to rely on the data I was getting in the back end of sessions for my fueling strategy rather than the ones I was receiving early in sessions.
2. My skin temp was closely tied to my sweat rate. No surprise there. But what was interesting was during long runs my skin temp stayed relatively constant and low, however when I ran off the bike the skin temp increased rather quickly. I had to assume that I was going to lose more fluids and electrolytes during the run portion than I was going to during my typical long run sessions.
3. My sweat rate was tied closely to\ the intensity levels. During race pace intervals, I was losing 50-60oz/hr on the bike while during the recovery periods I was losing 20-30oz/hr. During a standard long run session, I was losing 50-60oz/hr  during race pace intervals, but in some brick sessions I lost over 80oz/hr. The latest update allowing the hDrop to connect with my Garmin was extremely helpful on this front!

I tracked as many workouts and sauna sessions as I could and used that data to set my fueling plan for my race simulation sessions. These days are just as important from a nutrition front as they are from any fitness you gain from the day. In the lead up to IMNZ, I did four race simulation sessions which include a long bike followed by a long run where I practiced as closer to my race day nutrition plan as possible. The first session was a colder day and I still managed to under fuel. My HR was drifting up and my pace was drifting down on the end of the run. The final two sessions were fortunately days that were going to be similar to what I expected IMNZ to be like and I was able to finish both sessions feeling like I had nailed the nutrition aspect really well.

Using the hDrop, I was able to get valuable insights to help dial in my race day nutrition and hydration strategy for IMNZ. As I mentioned earlier, it’s best to have a fueling strategy that match the conditions of the course. Thankfully, I started out with a course with a relatively benign weather profile, but I’ve got a few warm races on tap this season (Ironman Texas and Kona!). So stay tuned for a discussion on how I used the hDrop information to guide my heat adaptation protocol and adjust my plan for racing in higher heat and humidity. 

Also, be sure to check out the hDrop website for more information on the device and how it works HERE. You can use code MATTHANSON10 to save 10% on your order.