What to take 40 minutes before a marathon
The pre-race window is a convergence of pharmacokinetic curves: gastric emptying, caffeine peak, anserine absorption, hydration equilibrium. Most of the discipline is not what to add. It is what not to.
Why forty minutes
The window is not arbitrary. It is the point where the four most-relevant absorption curves of a marathon morning all reach the same useful place.
A liquid carbohydrate dose taken with adequate water clears the stomach into the small intestine inside twenty to forty minutes.1 Caffeine, taken orally, reaches its plasma peak between thirty and sixty minutes after ingestion in most adults.2 Anserine, taken at 30 mg/kg by mouth, peaks in plasma between thirty and sixty minutes — the same window — and survives long enough to reach working muscle from outside.3 The water you drank with all of the above has equilibrated through the gut wall and reached the working tissues within twenty minutes.
The forty-minute mark, then, is the conservative center of all four curves at once. Take everything at the seventy-minute mark, and the carbohydrate is mostly absorbed but the buffering and caffeine still have headroom. Take everything at twenty minutes, and the gastric load is still in the stomach when the gun goes. Forty is the working middle. The athletes who have practiced it know why.
A second reason matters: forty minutes is the back end of a normal pre-race warm-up. The athlete is already moving. Blood is being shunted to working muscle. Gut motility is slowing. The stack arrives at the right time to be absorbed before the gut effectively closes for business.
The non-negotiables
The first version of this section is what not to do. There is more downside avoidance available on race morning than upside, and the cost asymmetry is severe. A gel that works fine in training but rebels on a nervous race-morning stomach can cost twenty minutes. The stack that adds half a percent and the misstep that costs four percent are not symmetric trades.
- Eat new food. Not a new gel brand. Not a new electrolyte. Not the free banana at the start line that you wouldn't have eaten at home. The gut on race morning is not the test environment for novelty.
- Eat solid food. Inside 60 minutes, gastric emptying of solids slows enough to leave a load sitting at the start. Fiber, fat, and protein especially. Fluids and isotonic gels only.
- Start beta-alanine. The mechanism is chronic. A race-morning scoop does nothing for the race and may add paresthesia that distracts. If beta-alanine is part of the build cycle, take the daily dose later in the day.
- Take a new caffeine dose. If you do not normally train with caffeine, race morning is not the introduction. The cardiac arrhythmia and GI distress risk is small but real, and it converts a 4-hour effort into a 5-hour one.
- Over-hydrate. 400–500 mL in the final 30 minutes is enough. Past that, the bladder fills and the sodium dilution costs more than the hydration helps.
- Stretch hard. Static stretching inside 60 minutes of a hard effort has consistently been shown to reduce peak power slightly. Save mobility for the night before; dynamic warm-up is fine.
None of this is exotic. Almost every experienced marathoner could write the list themselves. It still gets violated, on race morning, more than the experienced athletes themselves want to admit. The reason is simple: race morning is anxious, and anxiety reaches for novelty. The discipline is to do exactly what you practiced. Nothing else.
The race-morning stack
Five components, taken in roughly the order below, between 50 and 30 minutes before the gun. The doses below are field defaults; the educated reader will already know how to tune them.
An isotonic carbohydrate gel or drink. Maurten's hydrogel technology is the most-cited reason elite marathoners can now tolerate 100–120 g/hr during the race itself; in the pre-race window, a 30–60 gram dose simply tops up liver glycogen and sets the gut up for the fueling that will follow during the race.
If you train with Maurten gels, take a Maurten gel here. If you train with another brand, take that brand. The principle is unbroken: nothing new on race day.
If you tolerate caffeine and have trained with it. The dose-response curve in the endurance literature is well-mapped: 3–6 mg/kg, oral, peaks 30–60 minutes post-ingestion.4 Effects on endurance performance are real and well-replicated — measurably better than the anserine and beta-alanine effect sizes, for reference. A 70 kg athlete is in the 200–400 mg range.
Tablets and gels with declared caffeine content are preferable to coffee on race morning. The dose is more controlled, and the GI load is lower.
This is the window the molecule was built for. Anserine, taken at 30 mg/kg, peaks in plasma between thirty and sixty minutes — and, because the methyl group on its imidazole ring resists serum carnosinase, the molecule survives circulation and reaches the working muscle intact.5 A 70 kg athlete dose is approximately 2.0–2.5 grams of anserine.
The Ghent group's published effect — 3 percent peak power, 4.5 percent peak torque on the 30 mg/kg / 60 min protocol — is small but real and statistically robust. Effect size is responder-dependent. Test in training, not in the race. See the companion essay, Anserine vs beta-alanine, for the full mechanism.
Enough fluid to wash the stack down and equilibrate, with enough sodium to retain it. The exact electrolyte product matters less than the principle: practice it in training. The athletes who arrive at the line dehydrated are usually the ones who overcorrected after a bathroom visit and stopped drinking entirely. Steady volume, modest sodium, no acute loading.
Stop drinking 15–20 minutes before the gun to clear the bladder one last time.
For athletes who have built a tolerance to it. Sodium bicarbonate is the most extensively studied acute buffer agent in endurance sport, and it works — but the dose timing is different from everything else on this list, and the gastrointestinal cost is non-trivial.6 A 90–180 minute pre-race window, split into smaller doses with water, is the conservative protocol.
This belongs in conversation with a coach or sports dietitian. The fail mode — sudden GI distress at mile 4 — is severe enough that it should never be experimented with on race day.
Maurten is the fuel in the tank.
Katsuo is the cooling system.
The full timing protocol
The stack, anchored in time, from the morning's first alarm to the gun.
A note on the Japanese version
The protocol above is the Western synthesis. The Japanese ultra-endurance community arrived at most of the same answers through a different door.
The category Japanese sports scientists call imidazole dipeptides — carnosine and anserine, packaged for athletes — has been on the shelves of Japanese sports-nutrition retailers for two decades. The athletes of the Trans Japan Alps Race and the UTMB Asia field have used the window with a 40-minute anserine dose, often alongside an isotonic carbohydrate from one of the domestic brands, since well before the Western performance literature caught up.
The reason is partly geography. Anserine is concentrated in the red muscle of migratory fish, and the skipjack tuna — katsuo in Japanese — has been the cultural and culinary backbone of the Japanese coast for centuries. Katsuobushi, dried fermented skipjack shavings, is the foundation of dashi, the broth that begins almost every traditional Japanese meal. The molecule has been swimming through the Japanese diet for so long that its emergence as a sports supplement is less a discovery than a formalization.
Western endurance science has arrived at the same forty-minute window from a different direction. The Japanese version has been there the whole time.
Race day is not training day
The single most important rule in this entire field guide is one you have already heard a thousand times. We repeat it here because every paragraph above is invalidated if it is not followed.
Practice the stack at the same time of day as the race start. Practice it before the longest workout of the build phase. Practice it with the same caffeine dose, the same gel brand, the same hydration vehicle, the same anserine dose. Note what worked. Note what didn't.
Then, on race morning, do exactly that. Not the version with the new gel a teammate handed you. Not the version with twice the caffeine because the friend in your corral swears by it. The version you practiced. Nothing else.
If this field guide reads conservatively, that is by design. Race day rewards the conservative athlete who arrived with a stack they trust. It punishes the bold one who improvised at 5:30 a.m.
Frequently asked
Built like a skipjack.
Race Day · No. 003 · Companion to Anserine vs beta-alanine
- 1Jeukendrup, A.E. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 44(S1), S25–S33. Gastric emptying kinetics of isotonic carbohydrate solutions.
- 2Spriet, L.L. (2014). Exercise and sport performance with low doses of caffeine. Sports Medicine, 44(S2), S175–S184. Caffeine pharmacokinetics and the 3–6 mg/kg ergogenic dosing window.
- 3Blancquaert, L., Baba, S.P., Kwiatkowski, S., et al. (2021). Acute supplementation with carnosine and anserine improves repeated sprint performance. Journal of Applied Physiology, 130(2), 462–471. Ghent. The 30-minute pre-effort acute protocol.
- 4Maughan, R.J., Burke, L.M., Dvorak, J., et al. (2018). IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine, 52(7), 439–455.
- 5Yamaguchi, G.C., Nemezio, K., Schulz, M.L., et al. (2022). Dose-response effects of acute imidazole dipeptide ingestion on repeated-sprint performance. Journal of the International Society of Sports Nutrition, 19(1), 87–101. The 30 mg/kg / 60 min dose-response protocol.
- 6Carr, A.J., Hopkins, W.G., Gore, C.J. (2011). Effects of acute alkalosis and acidosis on performance: a meta-analysis. Sports Medicine, 41(10), 801–814. Bicarbonate effect sizes and dosing protocol guidance.