The athlete and the goal will always dictate the training and nutritional program. Each athlete is unique, and so should their program reflect that. For the sake of our discussion, we are going to be only looking at those who have aspirations to compete in the sport of CrossFit. With that being said, we need to look at the tasks and training that go into competing in that sport to dictate what type of fuel sources will serve them best. The sport of CrossFit includes a wide range of tasks that include but are not limited to: Absolute strength lifts, strength speed maxes, extended aerobic power, barbell cycling work at low and high loads, high power glycolytic work, middle zone glycolytic/threshold work, varying muscle endurance contractions, CP-battery contractions to name a few. When looking at these, we see a broad spectrum of energy demands on the athlete. Without going down a rabbit hole of what defines high intensity and how that varies for everyone, suffice to say the sport of CrossFit presents tasks that demand ample amounts of energy and output from athletes. With that being said, we are going to need specific nourishment to fuel those tasks and recover from them effectively so we can do them again tomorrow.
Now, what is the most optimal fuel source for the body when output is high? Well, let’s recall biology 101, ATP is the energy currency of the body. We use that molecule to perform all cellular activities. The faster we can break it down and rebuild it the more fuel we will have available. This will allow us to work at a higher rate for longer periods of time. In an overly simplified description looking at only one aspect of fatigue, as there are arguably 9 different components that go into fatigue (see James FitzGerald’s fatigue model for more insight), when people need to slow down their muscle tissues are not able to utilize, recycle, and produce enough ATP to sustain the output they are currently demanding on the working muscle tissues. One of the ways we can speed up this process is through optimal fuel intake to ensure we have the supporting pieces to fuel the processes needed to derive energy for the body. Oxidation, the process of breaking down molecules via oxygen, occurs in the body as such:
1st – Alcohol – the body can’t store it due to its toxicity so all processes are halted to clear it from the system
2nd – Carbohydrates – preferential source for energy production as it is the most efficient molecule for conversion
3rd – Proteins – The body doesn’t store much protein, some amino acids, more so utilized for various processes outside of energy production
4th – Fats – Lastly, fat. Has more energy per gram but doesn’t burn as efficiently. The body prefers to store it if it doesn’t need more fuel
The maximum rate of ATP synthesis, the body’s ability to produce more energy, from fat oxidation (breaking down fat via oxygen) is about 0.40 mol of ATP per minute. In comparison, ATP synthesis from glucose oxidation can generate 1.0-2.0 mol per minute; roughly a 2 to 5-fold difference (1). During CrossFit style training, the rate of ATP synthesized from free fatty acids cannot match the rate of ATP needed to fuel muscular work. Further, if an athlete became fat-adapted, where the body was preferential to utilizing fat for fuel, there would be a decrease in pyruvate-dehydrogenase activity. This enzyme is the first step in the process of linking the glycolysis metabolic pathway to the citric acid cycle (TAC). The TAC is the step before oxidative phosphorylation (electron transport chain) where we create the largest amount of ATP, 30 to 36 ATP’s yielded from 1 glucose molecule. Why is this important? Decreased levels of pyruvate-dehydrogenase will impair rates of glycogen breakdown (2). This will reduce glucose availability to fuel training (3). As Alan Aragon states, “Becoming fat-adapted results in being carb-impaired; it’s not an ideal physiological trade-off.” And continues, “This is why low-carb/ketogenic diets can be detrimental to sports that require continuous or intermittent high-intensity efforts” (read: CrossFit).
Knowing now that carbohydrates are the most preferred and efficient source of fuel for the body for the sport of CrossFit, let’s look at prescriptions around carbohydrate fueling. It’s worth repeating, all training and nutritional prescriptions need to be individualized as everyone is unique and will have differing demands. So, don’t take these as gospel but as general ideas for prescription.
First, we want to find out what the caloric demands are for the athlete. That will give us an idea of how much food they will need to be intaking, first, before we start to give percentages of macronutrients.
Very Active Athletes (8-12+ sessions per week)
Maintaining bodyweight = BW x 18-20
Gaining Weight = BW x 22-24
Active Athletes (5-8 sessions per week)
Maintaining bodyweight = BW x 16-18
Gaining Weight = BW x 20-22
For each athlete, it would be prudent to start on the lower end of caloric intake to see how the body handles that amount of food. From there, titration of calories over a week period would be a prudent approach if more is needed. Before adjusting macronutrient intake, the pieces you always want to be monitoring are: sleep quality and quantity, training quality and results, mood, digestion, arousal, energy throughout the day, bodyweight, and inflammation. Those KPI’s (key performance indicators) will ensure the athlete is moving in the right direction and the fuel they are intaking is on point.
When looking at amount of carbohydrate intake per day, this can vary drastically depending on a multitude of factors: how lean are they, how much training are they doing on a weekly basis, how much training are they doing per day, what type of sessions are they doing the most in their week, how old are they, what gender are they, what’s their heritage/background (just to name a few). All of these questions are going to dictate how much and how well they will handle carbohydrate intake. Let’s remember, we are discussing this with the CrossFit athlete in mind who for the most part will be training twice a day multiple times per week.
General Recommendation for CrossFit Athletes:
45-55+% of daily caloric intake coming from carbohydrates
2 – 2.4 x BW = daily carbohydrate intake
-205# male = 410 grams per day (as a starting point)
-150# female = 300 grams per day (as a starting point)
*To create context around what type of work an athlete would be doing to need that many carbohydrates, see below for an example of the 1st day of a 3 day weekend simulation in preparation for the CrossFit Games and/or CrossFit Sanctional Event:
5 sets @ 85%/Sustained Power:
20 Cal AB
10 Hang PC to OH @ 115#
10 Bar Facing Burpees
40 Wtd DU’s
10 BJO @ 24”
10 WB @ 30# to 10’
20 Cal Row
-rest/walk 3 min b/t set-
1 Squat Snatch every 90 sec x until tough single for the day
*Perform 4 Bar Facing Burpees before each lift
*Start @ 205, build 5-10# per set
For Time @ grind:
HSW Obstacle Course
PC to OH @ 225# -singles
5 min rest
For Time @ grind:
Strict pHSPU to 12” Deficit
D Ball Over Yoke @ 150#
1000m Run on Trueform
100m FW @ 115#/hand
30 BJSD @ 36”
100m Yoke Carry @ 550#
30 BJSD @ 36”
100m Double KB FR Carry @ 32kg/hand
1000m Run on Trueform
5 rounds for time @ high effort:
15 OHS @ 115#
12 Cal AB
*This should give you an idea of the type of work an athlete would be doing who needs to be consuming over 400g of carbohydrates per day (male athlete in the training example above). We would consider this the higher end of the spectrum with regards to training volume and amount of carbohydrates consumed per day.
While that may seem high for some people, that’s just a starting point. In the literature, carbohydrate prescriptions for elite level athletes in high-intensity sports can fall under the following prescriptions:
Immediate recovery after exercise (if training more than once in the day): 1-1.2g of carbs x kg per hour for 4 hours
Daily recovery: Moderate duration/low-intensity training: 5-7g of carbs x kg per day
Daily recovery: Moderate to heavy endurance training: 7-12g of carbs x kg per day
Daily recovery: Extreme/Tough training: 4-6+ hours of training (10-12+g of carbs x kg per day)
*Take this in context; 4-6 hours of intense work, Tour de France riders as an example, who will need upwards of 1000g carbohydrates to refuel, maybe more. Worth mentioning to give perspective on how valuable and important optimal carbohydrate intake is for sport performance.
“When the period between exercise sessions is less than 8 hours, the athlete should begin carbohydrate intake as soon as practical after the first workout to maximize the effective recovery time between sessions.” (4)
“During longer recovery periods (24 hours), the athlete should organize the pattern timing of carbohydrate-rich meals and snacks according to what is practical and comfortable for their individual situation. There is no difference in glycogen synthesis when liquid or solid forms of carbohydrate are consumed.” (4)
We need to understand the goal and the athlete before we start to think about what fueling will be necessary. Once that is known, we can then look at what goes into that sport. With the CrossFit athlete in mind, we know the sport demands a broad range of metabolic tasks that will require adequate resources to fuel and recover from. We know from research that ATP synthesized from glucose is roughly a 2 to 5-fold increase in ATP per minute (1-2.0 mol per min) compared to fat oxidation (0.4 mol per min). We know from research that becoming fat-adapted results in being carb-impaired, which becomes a poor physiological trade-off when considering the demands of the sport. We know the daily caloric demands for these athletes will be higher to promote recovery and growth. By extension, carbohydrate intake will be making up close to half, if not more, than their daily caloric intake. Before we blindly add more carbohydrates, remember to monitor the major KPI’s: sleep quality and quantity, training quality and results, mood, digestion, arousal, energy throughout the day, bodyweight, and inflammation. These pieces will give direct feedback on how the body is responding to the stress it is imposed and how well it is recovering. This will dictate the direction fuel utilization needs to go for the athlete. Lastly, everyone is unique and their prescriptions must reflect that.
Alan Aragon’s Research Review
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