Matt Hanson on Sweat Testing and Race Fueling With hDrop

In this post, you will get the perspective of Matt Hanson on Sweat Testing and Race Fueling With hDrop. Matt Hanson’s real-world race notes are a strong starting point. Here is the deeper physiology and decision framework that helps athletes turn those notes into repeatable performance. A review of Matt’s experience during his 3rd-place finish at IRONMAN New Zealand 2026 and his qualification for Kona.

Matt Hanson recently published Dialing in Race Day Fueling with hDrop, where he described rebuilding his fueling strategy around race-specific conditions and hDrop data. In that post, he highlighted three practical observations from his own training and race simulations: sweat concentration changed over session duration, sweat rate shifted with intensity, and bike-to-run transitions altered thermal and fluid stress.

Those are exactly the right questions to ask. This article goes one layer deeper: what the peer-reviewed literature says about why these changes happen, how large they can be, and how to build a hydration protocol that remains robust when race conditions do not match your plan.

Matt is a professional triathlete and coach with an exercise science background. He has a strong background in athletic training, human performance leadership, and university teaching in sports nutrition and exercise physiology. His racing background includes professional IRONMAN wins and North American championship-level results. He is a multi-time IRONMAN champion and former exercise science professor.

Now, let’s go deep into the post review from Matt.

Matt has been clear that race fueling should be built around the demands of the specific course, not just the event distance. As he writes, he has “always been a believer” in having nutrition “specifically for the course, not just for the distance,” because “each course is going to present different demands” that fueling needs to address. That perspective matters because race day needs are shaped by much more than mileage alone. Heat, humidity, wind, terrain, pacing, and sun exposure can all change what an athlete actually needs to perform well.

Matt also points out that sweat rate and electrolyte loss should not be treated as static numbers. In his article, he explains that “sweat rate and electrolyte concentrations change” with fitness, exercise intensity, environmental factors like heat and humidity, and even the sport itself. He also notes that sweat rate on the bike can differ from sweat rate on the run because airflow changes the body’s cooling demands. That is an important reminder for athletes who rely on one fixed hydration number across every workout and race scenario.

Another practical point Matt highlights is that different race segments can place different thermoregulatory demands on the body. He observed that during long runs his skin temperature stayed relatively stable, but “when I ran off the bike the skin temp increased rather quickly.” That observation aligns with the broader understanding that bike-to-run transitions are not physiologically identical to standalone running, in part because airflow, heat dissipation, and movement demands differ across disciplines. While skin temperature alone does not prove greater fluid or sodium losses, it does suggest that athletes may experience different heat strain and hydration demands during the run portion of a race than during a typical standalone run.

Matt also emphasizes that the best fueling plan is not simply the most aggressive one, but the one the body can actually absorb. As he puts it, “each individual gut can only handle so much osmotic load” which is why athletes need to find the right balance of carbohydrate, electrolytes, and water without compromising gastric emptying. He goes on to explain that in hotter and more humid races, higher sweat losses may require adjustments in fluid intake or carbohydrate concentration so the gut can continue processing fuel effectively. In practice, that means gut tolerance is often just as important as the physiological target on paper.

Fueling should be course-specific, not distance-only. Environmental heat load, humidity, wind, radiant heat, terrain, and intensity distribution all affect fluid and sodium needs. Consensus hydration guidance has emphasized individualized plans for years, specifically because inter-athlete variability is high and context-dependent [2].

Sweat rate and sweat sodium are variable, not static constants. Large inter-individual and intra-individual variability is repeatedly documented, including shifts by sport mode, exercise intensity, and environmental strain [1,3,7].

Bike-run transitions can materially change heat and fluid strain. Even when pace appears similar, metabolic cost, airflow, and thermoregulatory load differ across disciplines. Practical implication: using one fixed “hourly number” for all race segments is often suboptimal [1,2].

Gut tolerance is the bottleneck as often as physiology. High carbohydrate and sodium plans only work if gastric emptying and intestinal absorption keep pace. Gastrointestinal complaints are common in endurance sport and can become race-limiting [5,6].

The evidence base: what changes during long-course racing

Hydration planning lives at the intersection of thermoregulation, circulation, substrate delivery, and GI function. The literature supports four key realities.

First, dehydration effects are real but context-sensitive. Meta-analytic work shows performance costs can appear with body water losses, especially with longer efforts and greater thermal load, but outcomes vary by protocol and ecological validity [4]. This helps explain why some athletes can finish strongly above the classic 2% body-mass-loss threshold while others deteriorate earlier.

Second, sodium replacement is a risk-management variable, not a one-number target. Sweat sodium concentration spans very wide ranges in athletes, and total sodium loss depends on concentration and sweat rate [1,7]. Overly aggressive water-only intake can increase risk of exercise-associated hyponatremia, especially in prolonged events [8].

Third, carbohydrate delivery supports intensity, but dose and format must be practiced. Multiple transportable carbohydrate strategies can raise exogenous carbohydrate oxidation and support prolonged performance, but individual tolerance and concentration matter [9].

Fourth, the GI system is trainable but vulnerable. Endurance athletes frequently report GI symptoms, and severity can rise with heat, intensity, or excessive fluid/carbohydrate concentration. “Nutrition in training” is essential, not optional [5,6].

A science-first hydration model for long-course racing

Hanson’s post emphasizes building from race simulations. The most reliable framework is a three-loop model:

1. Baseline loop: establish discipline-specific sweat and fueling anchors in training.
2. Stress loop: repeat in hotter, higher-intensity, and brick conditions.
3. Decision loop: convert live signals (pace/power, skin temp trend, sweat metrics, GI status) into small intake adjustments.

This approach avoids two common failures: overfitting to one test session, and underreacting when race reality diverges from forecast.

Practical protocol for athletes

1. Profile your baseline. In at least 3-5 sessions, measure pre/post body mass, intake volume, session duration, and condition notes. If available, include sweat sodium monitoring/testing [1,3,7].
2. Build discipline-specific targets. Keep separate bike and run estimates. Do not assume equivalence just because average race intensity looks similar.
3. Train carbohydrate delivery progressively. Practice race-intended dose and composition weekly; do not introduce an untrained high-carb strategy on race day [9].
4. Anchor sodium to losses and risk profile. High-sweat or high-sodium-loss athletes need denser replacement plans, especially in heat [1,2,8].
5. Rehearse heat and humidity scenarios. Include at least two race-simulation sessions in expected conditions, exactly as Hanson described.
6. Create a trigger sheet. Predefine 3-4 triggers and response actions (for example: “HR drift + rising heat + dry mouth” -> increase fluid and sodium increment).
7. Protect against both extremes. Avoid both under-drinking and over-drinking. Persistent water-only overconsumption is a known hyponatremia risk [8].
8. Audit every key session. Record what happened, not what was planned. Update targets by trend, not one workout.

How hDrop data can improve decision-making

Hanson’s post frames hDrop as a bridge between one-time testing and ongoing race-specific calibration. That is the right use case. Continuous or repeated field measurements can help athletes detect drift across phases, distinguish bike versus run demands, and adapt intake before major pace loss develops.

Technology does not replace physiology principles; it operationalizes them. The winning model is still the same: measure, rehearse, adjust, and re-test.

Key takeaways

• Matt Hanson’s Ironman New Zealand qualified him to Kona, and his post is directionally aligned with current hydration science: race-specific and data-driven.
• Sweat rate and sodium losses are dynamic; bike and run plans should not be copied from one another.
• Carbohydrate, fluid, and sodium must be co-designed with GI tolerance, not treated as separate silos.
• Use field simulations in race-like conditions to pressure-test your protocol.
• Do not chase one fixed number; build trigger-based decision-measured rules for race day.

Sources

1. Baker LB. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Med (2017). https://doi.org/10.1007/s40279-017-0691-5
2. American College of Sports Medicine Position Stand. Exercise and Fluid Replacement (2007). https://pubmed.ncbi.nlm.nih.gov/17277604/
3. Baker LB et al. Comparison of regional patch vs. whole body washdown for measuring sweat sodium and potassium loss during exercise. J Appl Physiol (2009). https://doi.org/10.1152/japplphysiol.00197.2009
4. Goulet EDB. Effect of exercise-induced dehydration on endurance performance. Br J Sports Med (2013). https://doi.org/10.1136/bjsports-2012-090958
5. de Oliveira EP, Burini RC, Jeukendrup A. Gastrointestinal Complaints During Exercise: Prevalence, Etiology, and Nutritional Recommendations. Sports Med (2014). https://doi.org/10.1007/s40279-014-0153-2
6. Mlinaric J, Mohorko N. Nutritional strategies for minimizing gastrointestinal symptoms during endurance exercise: systematic review. J Int Soc Sports Nutr (2025). https://doi.org/10.1080/15502783.2025.2529910
7. Barnes KA et al. Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes. J Sports Sci (2019). https://doi.org/10.1080/02640414.2019.1633159
8. Hew-Butler T et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference (2015). https://doi.org/10.1136/bjsports-2015-095004
9. Jeukendrup AE. Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metab Care (2010). https://doi.org/10.1097/MCO.0b013e328339de9f
10. Matt Hanson. Dialing in Race Day Fueling with hDrop (2026). https://matthansonracing.com/dialing-in-race-day-fueling-with-hdrop/
11. Coach Matt Hanson profile. https://matthansonracing.com/meet-the-coaches/coach-matt-hanson/
12. IRONMAN Pro Series athlete profile: Matt Hanson. https://www.ironman.com/proseries/triathletes/matt-hanson