How Does Caffeine Aid Endurance Performance? Dosage, Timing, and Carbohydrate Combination

1Why Caffeine Works: It Blocks "Fatigue" Signals

First, a basic concept: your body uses a molecule called adenosine to tell your brain "you're tired." The longer you exercise, the more adenosine accumulates, and the more frequent the "fatigue notifications" your brain receives, making you feel more tired and wanting to slow down.

Caffeine's role is to occupy adenosine receptors prematurely—like intercepting "you're tired" notifications on a phone line. Adenosine is still present, but the brain temporarily doesn't receive fatigue signals. Your physical capacity remains the same, but the perceived effort significantly decreases.

Caffeine is one of the most researched ingredients in sports nutrition: an umbrella review covering 21 meta-analyses confirmed that caffeine has positive effects on various athletic performances, particularly clear for running endurance. The International Olympic Committee consensus also lists caffeine as an evidence-backed sports supplement.

Interpretation: For you, caffeine doesn't "magically create energy"; rather, it makes existing energy easier to access—the same pace with less perceived effort, or maintaining the same perceived effort for longer.

• Grgic J, et al. Br J Sports Med 2020, 54(11):681-8
• Wang Z, et al. Nutrients 2022, 15(1):148
• Maughan RJ, et al. Br J Sports Med 2018, 52(7):439-55

2How Much Is Effective: 3–6 mg per kg is the Sweet Spot

Caffeine dosage is calculated by body weight, not just a standard cup. The consensus effective range from research is 3–6 mg per kg of body weight:

(One cup of instant coffee contains approximately 60–80 mg of caffeine; the above is a rough conversion for illustration.)

Interpretation: More is not always better—exceeding 6 mg/kg will not increase effectiveness, but side effects like insomnia, heart palpitations, and gastrointestinal discomfort will rise. For most people, 3–4 mg/kg is sufficient; individual responses vary greatly, so start with a low dose during training.

• Maughan RJ, et al. Br J Sports Med 2018, 52(7):439-55
• Grgic J, et al. Br J Sports Med 2020, 54(11):681-8
• Chen et al. J Int Soc Sports Nutr 2024 (Dose refinement and CYP1A2 gene differences)

3When to Take It: Approximately 60 Minutes Before the Race, or During the Latter Half of the Race

After oral intake, caffeine blood concentration peaks in approximately 60 minutes, has a half-life of 4–6 hours, and its effects can last for 3–4 hours (Endurance Sports Nutrition Knowledge Base §4.2). There are two approaches to timing:

• Before the race: Take the initial dose approximately 60 minutes before the start gun to ensure concentration is in effect early in the race.
• During the latter half of the race: Fatigue is most severe during the later stages of long races—at this point, a dose of caffeine can "sustain" you through the final stretch. Elite marathon runners commonly use caffeine-containing energy gels for a boost in the later stages (Evidence of Supplementation Strategies for Elite Marathon Runners).

Interpretation: Both can be used—a foundational dose before the race and a boost in the later stages. The key for the later-stage boost is "the moment of most severe fatigue," not a fixed kilometer mark; for full marathon runners, this is roughly within the last 10 kilometers.

• Endurance Sports Nutrition Knowledge Base §4.2 Caffeine (Timing and Half-Life)
• Evidence of Supplementation Strategies for Elite Marathon Runners (Mid-to-late stage boost during the race)

4Half-life: What 4–6 Hours Means

"Half-life" is a basic pharmacokinetic concept: the time it takes for the body to reduce the caffeine concentration in the blood by half. For caffeine, it's about 4–6 hours—meaning that 4–6 hours after intake, half of it still remains in the blood.

Taking 200 mg as an example:

Interpretation: The half-life determines two major things—

• On Sleep: If you race in the morning and take caffeine 60 minutes before, it will be mostly cleared before bedtime, not affecting sleep. However, if you drink 200 mg after 3 PM for training, about half will still be in your blood at 9 PM, potentially disrupting sleep that night.
• For Staged Supplementation: The effect of the first dose will gradually wane in long events (over 3 hours)—thus, a second dose for a boost in the later stages is logical: supplement when the first dose is fading to maintain the effect. This is precisely what elite marathon runners do.

Individual Differences: The CYP1A2 gene determines metabolic speed; the half-life can fluctuate between 2–7 hours. Smokers metabolize faster (shorter half-life), while those taking oral contraceptives metabolize slower (longer half-life)—your "effective dose" and "how long you stay awake" could be twice or half that of others.

• Endurance Sports Nutrition Knowledge Base §4.2 Caffeine (Half-Life)
• Chen et al. J Int Soc Sports Nutr 2024 (CYP1A2 Gene)

5With Carbohydrates: More Than the Sum of Their Parts

Caffeine and carbohydrates work through different pathways: carbohydrates provide energy, and caffeine reduces perceived effort—they can be used simultaneously, with synergistic effects:

• Diagram · Caffeine + carbohydrates are shown with an approximate middle value of 119 for research-indicated improvement (relative to pure carbohydrates at 100), with data detailed in this chapter's sources.

Interpretation: Research indicates that adding caffeine to sports drinks can increase work capacity by approximately 15–23% more than carbohydrates alone, while also lowering subjective fatigue. Another study found that caffeine can also increase the oxidation rate of exogenous carbohydrates (ingested carbohydrates)—by about 26% in the late stages of exercise. For you: a caffeine-containing energy gel accomplishes two things simultaneously—replenishing carbohydrates and reducing perceived effort.

• Cureton KJ, et al. Int J Sport Nutr Exerc Metab 2007, 17(1):35-55
• Yeo SE, et al. J Appl Physiol 2005, 99(3):844-50

6An Overview of SiS Products Containing Caffeine

SiS offers four caffeine-containing products, categorized by "carb requirement" and "scenario":

Selection logic (answer two questions first):

Interpretation: The four products are not ranked by "more expensive means better," but by different needs—first ask "do I need carbohydrates for this effort," then "do I also need to hydrate/maintain focus," and the answer will naturally lead to one of the products.

• SiS Official Product Pages, Nutritional Labels (scienceinsport.com)

7Who Should Be Cautious: Sensitive Individuals and Afternoon Doses

Caffeine is not suitable for everyone. Here are three scenarios where caution is advised:

• Sensitive individuals: People who experience heart palpitations, tremors, or significant anxiety should start with a low dose or avoid it altogether.
• Afternoon and before bed: With a half-life of 4–6 hours, caffeine intake after 3 PM may affect sleep that night; insufficient sleep itself is detrimental to endurance performance.
• Genetic variations: The CYP1A2 gene determines how quickly caffeine is metabolized, with significant differences in response between "fast metabolizers" and "slow metabolizers"—what's an effective dose for one person might be a sleep-disrupting dose for another.

Interpretation: The golden rule for caffeine, just like carbohydrates, is—never try anything new on race day. Any dosage, any product, should first be tested during training to confirm tolerance and effectiveness before being used in a race.

• Chen et al. J Int Soc Sports Nutr 2024 (CYP1A2 Gene Differences)

Conclusion: Three Steps for Caffeine Use

Dosage (3–6 mg per kg, start low) → Timing (approx. 60 minutes before race, boost in later stages of long races) → Product (choose from four caffeine products based on need, see §⑥).

• Beginners: Start with 3 mg per kg and confirm tolerance during training.
• Marathon/Long-distance: Use a caffeine-containing energy gel for a boost in the later stages; for high carbohydrate demand scenarios, choose BETA Fuel + Nootropics (see §⑥ for product selection).
• Any new product: Test during training first, never try anything new on race day.

• Grgic J, et al. Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses. Br J Sports Med 2020, 54(11):681-8. PMID:30926628. DOI:10.1136/bjsports-2018-100278
• Wang Z, et al. Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-Analysis. Nutrients 2022, 15(1):148. PMID:36615805. DOI:10.3390/nu15010148
• Maughan RJ, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med 2018, 52(7):439-55
• Cureton KJ, et al. Caffeinated sports drink: ergogenic effects and possible mechanisms. Int J Sport Nutr Exerc Metab 2007, 17(1):35-55. PMID:17460332. DOI:10.1123/ijsnem.17.1.35
• Yeo SE, et al. Caffeine increases exogenous carbohydrate oxidation during exercise. J Appl Physiol 2005, 99(3):844-50. PMID:15831802. DOI:10.1152/japplphysiol.00170.2005
• Chen et al. Caffeine dose refinement and CYP1A2 genotypes. J Int Soc Sports Nutr 2024, 21(1)