Issue #15: Train Harder with High-Carb

✍️ Author’s Note

Welcome back to The Threshold Lab, where each week we dissect a training topic, dig into the research and translate it into practical strategies. I’m Stephen Pelkofer, an aspiring HYROX Elite 15 athlete and science/data nerd. This week’s edition is all about carbohydrates, not just for marathoners on race day, but for training sessions themselves. You can thank my training partner (🦝) and some recent podcast listening for this topic.

🏃 Beginner HYROX Endurance Program

I recently partnered with Christian Harris (former Crossfit Games athlete) Move Fast Lift Heavy to build an endurance program that is ideal for beginner to intermediate endurance and HYROX competitors. This is a 12 week program with simple but proven progressions that will get you ready for race day.

The program starts at about 80 minutes of running and builds up to 3-3.5 hours by the end, with a HYROX specific block in the 6 weeks leading up to a race. You can purchase the program on TrainHeroic here! You can also check out all of the MFLH programs available here.

👨‍💻 Introduction

Topic: Fueling with Carbs to Train Harder

Endurance athletes have long relied on “carb loading” and in-race fueling for longer events like the marathon, but there is an increasing interest in using a high carb fueling strategy for training purposes. As I have worked to increase my training volume and intensity this offseason, I have been upping my carb intake quite a bit to try and keep up with expenditure. Some people are still anti-high-carb, mainly for general health reasons (high carb means extremely high sugar). While I think that is a fair opinion, the research is very clear: fueling with carbs lets you train harder, recover better, and go longer. If performance is a priority, this is the way. Period.

I read A LOT of research this week. Today’s issue is not focused on just one paper, but several that I spent my free-time reading 😁 – you can see the list of sources at the end of this post.

🔬 What the Science says about High Carb

Carbs During Workouts Boost Performance (Meta-analysis, 96 studies)

• Athletes who took carbs during endurance exercise went longer and faster.

• Works best for sessions longer than ~90 minutes, but even ~1-hour hard efforts can see small gains (including just rinsing your mouth with a carb mix lol)

• Lab Note: Aim for 30-60g carbs per hour during long runs or tough intervals. Mix sources (glucose + fructose) for faster absorption.

Carbs Let You Train Harder in Heavy Weeks (Achten et al., 2004 – runners)

• Runners on high-carb (8.5 g/kg/day!!) diets performed much better during a 7-day overload block compared to those on moderate carb diets (5.4 g/kg).

• The high-carb group slowed down less and felt less fatigued.

• Lab Note: When stacking hard sessions or a training camp week, fuel up with more carbs than you typically would – it helps you keep intensity high across the week.

Training Low vs Training High (Yeo et al., 2008 – cyclists)

• “Train-low” athletes (sometimes doing workouts with low glycogen) did show more fat-burning adaptations…

• But both groups improved performance equally after 3 weeks, and the “train-low” group struggled to hit high-intensity/high power during workouts.

• Lab Note: Occasional fasted runs might tweak your metabolism, but consistent carb fueling lets you train harder, which is going to lead to more performance gains.

Carbs vs. Keto in Elites (Burke et al., 2017 – race walkers)

• High-carb and periodized-carb diets (high-carb for key sessions, low for easy stuff) led to ~5% faster race times after 3 weeks.

• The low-carb and high-fat (keto) group saw no performance gains despite burning more fat.

• Lab Note: Elite or not, carbs are king for performance. Keto could make you a fat-burning machine but doesn’t make you faster.

Daily Training with Carbs vs. Without (Cox et al., 2010 – cyclists)

• The high-carb group improved performance the same as the low-carb group (~6%), but fueled athletes could hit workouts harder and improved their carb-oxidation efficiency.

• This adaptation supports sustaining high efforts where your body needs to generate energy quickly enough to maintain pace and power output.

• Lab Note: Training with carbs doesn’t always mean faster adaptations, but it lets you perform more workouts at a higher quality, which matters a lot for long-term progress.

Time for some lab notes ⬇️

🧪 Lab Notes

In every issue of this newsletter, the “Lab Notes” are going to be the protocols that you can apply to your training and routine right away. The goal of this section is to translate the science into actionable steps for the reader, whether you’re a recreational runner/HYROX competitor, or someone pushing the limits of their peak potential.

1. Fuel your long and hard sessions: This doesn’t just mean before, but during and after as well. You will be able to sustain higher power output if you (1) go into the session “carbed up”, and (2) consume 30-60g of carbs per hour of exercises. Elite endurance athletes like ultra runners and elite cyclists are consuming 100+g/hour… these sports have become eating contests.
   

2. Eat more carbs during heavy training blocks: When you have a big training week or a race‑specific block planned, bump your daily carb intake up. This helps maintain performance and mood and reduces the risk of feeling flat mid‑week. Being in a surplus is better than being in a deficit during peak training blocks.
   

3. Be careful with excessive sugar intake: More training = more carbs = more sugar. Timing of carbs matters – plan the high intake before, during, and right after training. Outside of training, focus on protein and fat needs as well as healthier carb options like sweet potatoes, quinoa, fruits, and vegetables. Performance is not everything.

That’s it for this edition of the Threshold Lab. Happy training!

References

1. Jeukendrup A. E. (2004). Carbohydrate intake during exercise and performance. Journal of Applied Physiology.
   

2. Achten J., Halson S. L., Moseley L., Rayson M. P., Casey A., & Jeukendrup A. E. (2004). Higher dietary carbohydrate content during intensified running training results in better maintenance of performance and mood state. Journal of Applied Physiology.
   

3. Yeo W. K., Paton C. D., Garnham A. P., Burke L. M., Carey A. L., & Hawley J. A. (2008). Skeletal muscle adaptation and performance responses to once‑daily versus twice‑daily endurance training sessions. Journal of Applied Physiology.
   

4. Akerström T. C., Fischer C. P., Plomgaard P., Thomsen C., van Hall G., & Pedersen B. K. (2009). Glucose ingestion during endurance training does not alter training adaptation related to substrate metabolism or performance. American Journal of Physiology: Endocrinology and Metabolism.
   

5. Cox G. R., Clark S. A., Cox A. J., Halson S. L., Hargreaves M., & Hawley J. A. (2010). Daily training with high carbohydrate availability increases rates of glycogenolysis during exercise. Journal of Applied Physiology.
   

6. Burke L. M., Ross M. L., Garvican‑Lewis L. A., Welvaert M., Heikura I. A., Forbes S. F., & Hawley J. A. (2017). Low‑carbohydrate, high‑fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. Journal of Physiology.