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The author, Chris Case, is preparing to race Dirty Kanza 200 on June 2. This is the second installment of a series of articles he’s writing on the physiological and nutritional demands of ultra-endurance events like this, as well as the gear he’ll use in the grueling 200-mile race across Kansas’s Flint Hills. See part one here. This series of articles is sponsored by 3T, Saris, and Enve. Case will ride a 3T Exploro aero gravel bike with an Enve wheelset and PowerTap power meter hub during the race.
Planning, practicing, and executing a race-day fueling strategy, particularly for endurance events, is one of the most daunting challenges an athlete faces. When riding for 12-plus hours and 200-plus miles at a race like Dirty Kanza, it is crucial for performance — and a pleasurable experience. For many, the day of the race will be the first time they push themselves to such extremes, making it difficult to know what, when, and how much to consume.
In my first attempt at DK200 in 2013, I had very little understanding of how I would cope with the nutritional demands. I consumed countless calories — some from bars and blocks, some from homemade treats, and others from drink mixes. Some of the unidentifiable globs were as hot as my back under a Kansas sun and as mushy as a compost pile. Yes, it was gross. At some point, my gut couldn’t take it anymore. I hit a wall; I dry-heaved a bit. Eventually I kept going, but I rode significant amounts of time without being able to consume anything, digging myself into a caloric deficit I would never escape. Because of that, I stopped having any kind of fun.
This time around, I plan to be better prepared.
I detailed how I’m reworking my physiology in the first installment of this series. With the help of VeloNews’s resident physiologist Trevor Connor (who is also my co-host on Fast Talk, the VeloNews podcast on training and sports science), as well as sports nutritionist Ryan Kohler and physiologist Jared Berg at the University of Colorado Sports Medicine and Performance Center, we recently analyzed my metabolism. This allowed us to better understand how my body utilizes energy (calories), which in turn will help inform how I can best meet the nutritional demands on race day.
Hopefully, by understanding my situation, you will be better equipped to dial in your fueling strategy at a race such as Dirty Kanza, or any ultra-endurance race.
Determining caloric needs
The first step I took to better understand my metabolism was to perform a metabolic test at the University of Colorado Sports Medicine and Performance Center. This was similar to the lactate profile test I performed for the first article: lactate levels were analyzed in my blood as I rode progressively harder, above and beyond my so-called lactate threshold. What was different about the metabolic test was that I wore a mask the entire time I was riding, from easy to hard. The mask was able to detect ventilation rate, oxygen consumption, and gas exchange. Basically, it determined what I was breathing in and out.
Using well-established equations, the ratio of carbon dioxide to oxygen was used to determine the ratio of carbohydrate and fat I burned as I rode, and how that ratio changed as intensity levels rose.
This so-called substrate utilization is key to thriving at a race like Dirty Kanza.
What did we find? My fat metabolism was decent through 149 beats per minute, and then dropped off as expected as intensity increased. When fat utilization (“burning”) is high, metabolic efficiency is high. It is important to have optimal fat utilization in order to rely less on carbohydrate metabolism.
“This carbohydrate utilization at moderate intensities could elicit a higher and faster glycogen utilization rate and therefore a faster depletion during prolonged exercise, increasing rates of fatigue,” Berg said.
To take things a step further, we next determined the number of calories I will need to consume during Dirty Kanza. To do that, it’s necessary to consider both the intensity and duration of the effort. Since the metabolic test determined how many kilocalories (Kcals) per hour I burned (separated into carbohydrates and fats; see figure 1) at different intensities, we used the results to calculate my expenditure for the race.
For example, if I average my zone 2 pace during Dirty Kanza, I will burn approximately 500 Kcals of carbohydrates per hour. Over the course of a 12-hour race (if I’m lucky!), that’s 6,000 total Kcals.
Generally speaking, this same calculation can be made for any event or workout I might do. (See below for generalized guidelines on planning for your race, particularly if you cannot find a facility at which to perform a metabolic test.) For example, say I plan to ride one hour on the flats before heading into a 45-minute climb, then retracing my route to return home. During the ride I’ll cruise for one hour at base intensity on the flats, before climbing for 45 minutes at threshold intensity, descending 30 minutes in active recovery, and then riding an additional one hour at base intensity to return home. Knowing the intensities and durations allows me to determine my caloric expenditure in the same way, just by adding together the components based on those known parameters.
Now that I know my caloric expenditure, I have to consider the energy I have already stored in my body. Most people have approximately 400-500 Kcals of carbohydrate stored in their liver. There, it is stored as glycogen. You deplete most of that fuel source while sleeping, so you’ll need to replenish it in the morning before the race. This fuel source can be sent to various parts of the body through the blood stream.
We also store carbohydrate as glycogen in our muscles. Unfortunately, once carbohydrate has entered a muscle it is locked there and cannot move to other muscles. (Technically, in fast-twitch fibers, it goes through glycolysis, gets converted to lactate, and then can be transported to other muscles or the liver where it is converted back to glucose.)
Males have approximately 55 percent of their muscle mass in their legs and females approximately 60 percent, which means the majority of stored glycogen is in the lower body.
For each kilogram of muscle mass, we store about six grams of glycogen. To approximate how much glycogen I have stored, we first determined my lean mass (weight, less fat, in kilograms). Then, we multiplied by 55 percent (since I’m male; use 60 percent if you are female). Next, we multiplied by six grams of carbohydrate per kilogram of weight to determine grams of glycogen. To convert to calories, we multiplied by 4.18.
A body composition test determined that my lean mass is 63.6 kilograms, and that I am nine percent body fat. The result? I have 799 Kcals of carbohydrates stored in muscle tissue.
Since we know approximately how many calories I have stored and how many I’m projected to burn, we can estimate the carbohydrate (in Kcals) I need to consume to successfully and optimally complete Dirty Kanza.
The bottom line? I should eat 392 Kcals of carbohydrates per hour. What’s that work out to? Approximately 95 grams of carbohydrate, which is equivalent to two packs of Clif Bloks and two bottles of Skratch per hour.
Improving metabolism and nutrition planning
Because fat oxidation is an aerobic process, training at zone 2 improves the power at which you can still rely on fat as fuel. A higher volume (typically 70-80 of total volume) of training in zone 2 will help increase mitochondrial volume and subsequent lactate and fat metabolism, which will increase performance potential at all intensities. This was detailed in the first installment of this series.
For those who cannot undertake a metabolic test, there are alternative means to help guide intake. Exercise physiologist and sports nutritionist Asker Jeukendrup has developed estimates of caloric expenditure for a given intensity and duration. Kohler suggests using those estimates as a starting point to developing a more personalized plan. Through trial and error, he recommends slowly working through key workouts consuming a quantity of fuel from the low end of the range first, and then steadily increasing intake.
“There is an ability to train the gut, to take in more,” Kohler said. “And then there are many other subjective things: Do you notice improvements in how you’re feeling? What’s the perceived effort and any improvements with higher intakes? Is power maintained better? If things improve as intake increases, then we keep going slowly upward until you find that sweet spot.”
Kohler is a proponent of testing race-day nutrition on training rides well before the event. For an event like Dirty Kanza, doing so in rides that last eight or 10 hours can be highly educational, assuming you have that luxury. It’s in the latter stages of a race where gastrointestinal (GI) stress can plague both performance and the pleasure of the experience as a whole. On these rides, pay attention to nutrition, hydration (which we’ll cover in a future article), and take note of when “taste fatigue” strikes. That phenomenon happens to nearly everyone at some point — sooner for some, later for others. As Kohler said, some athletes could eat nails and they’d be fine, so durable are their stomachs. Most athletes are not so lucky.
“When GI stress kicks up, hydration is the first thing I have people turn to,” Kohler said. “Many times, it’s easy to get underhydrated, especially if it’s a hot day and you’re out there for 12 or more hours. Piling in more calories is going to put you further down that rabbit hole of GI stress. Adding more fluid to the gut will help with gastric emptying. Ideally, you’re adding some sugar, some sodium, and some fluid all at the same time. If they come in together at the right time and in the right amounts, then they empty quickly which will help limit the GI stress.”
Hydration, and balancing the fluids, electrolytes, and calories you need in a well-coordinated fashion throughout a long day, is where we’ll turn to in our next installment of this series on training and racing Dirty Kanza 200.
More on nutrition
Though it doesn’t specifically pertain to race-day nutrition, the following Fast Talk podcast episode offers a deep discussion on nutrition in general. In it we discuss what we think is healthy and what isn’t. We talk about what foods to eat, our take on the question of wheat, nutrient density, and sugar. Unlike other episodes, in this show our resident physiologist and nutrition expert Trevor Connor is both the co-host and the guest of honor. His research in graduate school focused on many of these topics, and what he’ll share are his educated opinions.