The Benefits of Caffeine for Endurance Performance: Latest Meta-Analysis of 3-6 mg/kg Doses and Individual Variability

Based on peer-reviewed research from international sports science journals, this article provides an in-depth analysis of the effects of “caffeine supplementation” on athletic performance, combined with Taiwan-specific riding and race scenarios, offering actionable training nutrition advice.

Caffeine is the most well-evidenced legal supplement in the history of sports science, with over a thousand studies accumulated since 1907. It can enhance endurance, anaerobic performance, alertness, and pain tolerance. However, the real key question is not “does it work,” but “what dosage, what timing, and for whom is it most effective.” In recent years, large-scale meta-analyses have shifted focus toward dose-response curves and genotypic individual differences, overturning the gym myth that “stronger coffee is better.” In Taiwan’s environment, where bubble tea shops and convenience-store Americanos are ubiquitous, understanding precise dosing is especially practical.

In Taiwan’s endurance sports community—whether it’s climbing enthusiasts tackling the West Route to Wuling, long-distance riders on the East Route through the Huatung Valley, or participants in Sun Moon Lake circumnavigation, Taroko Marathon, and 226 km Ironman triathlons—the topic of “caffeine supplementation” matters because it directly determines whether you can maintain your pace in the latter stages of a race, avoid cramping and hitting the wall, and recover effectively between consecutive training days. Many amateur athletes pour all their effort into power training and equipment upgrades while overlooking nutrition—this “free margin for improvement.” In fact, when training volume and equipment are comparable, the quality of nutritional strategy is often the key variable separating finishing from DNF, and personal bests from blow-ups. This article will walk you through the complete context—from cellular molecular mechanisms and randomized controlled trial evidence to dose-response curves and practical application—debunking long-standing myths so that your fueling strategy is truly built on science.

Academic Research Review

Regarding the scientific exploration of “caffeine supplementation,” top international journals have accumulated rich and rigorous evidence. Below are several representative studies selected for their value in methodological design, sample populations, and strength of conclusions, which together construct our current understanding of this topic:

1. Doherty M and Smith PM (2004, International Journal of Sport Nutrition) conducted an early meta-analysis integrating 21 studies, confirming that caffeine improves endurance time-trial performance by approximately 12% on average.

2. Grgic J et al. (2020, British Journal of Sports Medicine) conducted an umbrella review integrating 21 meta-analyses, concluding that 3–6 mg/kg is the optimal supplementation range with stable effect sizes.

3. Southward K et al. (2018, Sports Medicine) meta-analysis indicated that caffeine’s overall effect size on endurance performance is g≈0.41, and that time trials (TT) have greater ecological validity than exhaustion tests.

4. Guest N et al. (2018, MSSE) used CYP1A2 genotyping and found that AA-type (fast metabolizers) benefited most in cycling time trials, while CC-type individuals may see no benefit or even impairment.

Looking at these studies collectively, the scientific picture of “caffeine supplementation” is not a single fixed conclusion but rather something continuously revised and deepened as research methods advance. Early studies mostly used laboratory-controlled time trials or exhaustion tests; subsequent research gradually introduced stable isotope tracing, muscle biopsies, functional magnetic resonance imaging (fMRI), and molecular biomarkers, allowing us to move from “observing phenomena” to “explaining mechanisms.” Notably, most high-quality studies employ randomized crossover designs, where each subject serves as both experimental and control, greatly reducing noise from individual differences. However, extrapolating research conclusions still requires caution: the responses of well-trained subjects in the laboratory may not fully apply to general amateur athletes; nor do the effects of a single acute intervention necessarily equate to long-term chronic adaptation. When reading the “effect sizes” and “statistical significance” of these studies, we must also distinguish between “statistically significant” and “practically meaningful”—a 1% improvement might determine medal placement in elite competition, but its significance is relatively limited for recreational riders.

Core Mechanisms

Caffeine primarily works by antagonizing adenosine receptors (A1, A2A). Adenosine accumulates during exercise and produces fatigue and drowsiness signals; caffeine competitively binds to these receptors, releasing this “brake,” thereby increasing central nervous system excitability, enhancing motor unit recruitment, and reducing pain perception. Additionally, it mildly increases fat mobilization and catecholamine release, but the old “glycogen-sparing” hypothesis has been weakened in modern research—the central nervous system mechanism is the main pathway.

To truly understand how “caffeine supplementation” affects athletic performance, we must return to physiology at the cellular and systemic levels. Athletic performance is the result of multi-system coordination: the cardiovascular system handles oxygen and fuel delivery, muscle cells handle energy conversion and mechanical contraction, the central nervous system regulates motor unit recruitment and fatigue perception, while the gut and liver form the hub of nutrient absorption and metabolism. The reason the aforementioned mechanisms translate into measurable performance differences is precisely because they act on one (or more) key links in this chain. The table below organizes the key points of action at different physiological levels for this topic, helping you build a complete mechanistic picture:

| Level of Action | Key Mechanism | Significance for Athletic Performance |

|—|—|—|

| Cellular/Molecular | Affects mitochondrial efficiency, enzyme activity, and signal transduction | Determines energy conversion efficiency and adaptation direction |

| Muscle Tissue | Regulates substrate utilization, buffering capacity, and contractile function | Affects sustainable power output and fatigue onset |

| Systemic Integration | Alters blood flow distribution, thermoregulation, and hormonal environment | Determines stability and safety during prolonged exercise |

| Central Nervous System | Regulates fatigue perception, drive, and motor unit recruitment | Affects “how tired it feels” and whether you can persevere |

Special emphasis should be placed on the two dimensions of “dose-response” and “temporal dynamics.” The same nutritional intervention, at different intake amounts and different intake timings, can produce vastly different or even opposite effects—this is precisely why many popular recommendations are one-sided. Only by understanding the mechanisms can we judge “when to use it, how much to use, and when to take it,” rather than blindly following trends.

Going further, the limiting factors of athletic performance shift dynamically with exercise intensity and duration: in short, high-intensity bursts, limitations often come from the phosphagen system and the accumulation of glycolytic byproducts; in multi-hour endurance events, limitations shift to the combined effects of glycogen depletion, rising core temperature, fluid and electrolyte imbalance, and central fatigue. The reason “caffeine supplementation” deserves in-depth exploration is precisely because it can specifically target certain of these limiting factors. This also reminds us that no nutritional strategy can be evaluated in isolation from the “exercise context”—a fueling rhythm suitable for a 40-minute criterium may not apply to a 6-hour climbing epic; and vice versa. The more thoroughly you understand the mechanisms, the more flexibly you can adjust across different race formats, rather than rigidly adhering to a fixed formula. This ability to “adjust according to context” is precisely the dividing line between amateur athletes and those who truly understand sports science.

Dose-Response Relationship

In sports nutrition, “the dose determines both the toxicity and the benefit.” Too low a dose fails to reach the physiological threshold and is futile; too high a dose may trigger side effects, gastrointestinal discomfort, and even interfere with training adaptations. The table below organizes the dose-effect correspondence for “caffeine supplementation” and serves as the most important quantitative reference when developing a personal fueling plan:

| Dose / Condition | Applicable Scenario | Key Recommendations |

|—|—|—|

| < 3 mg/kg | Low | Inconsistent benefits; only alertness improvement |

| 3 mg/kg | Minimum effective dose | Significant endurance performance improvement with low side effects |

| 3–6 mg/kg | Golden range | Maximized effects; well tolerated by most |

| > 9 mg/kg | Excessive | Palpitations, anxiety, gastrointestinal discomfort; no additional benefit |

From the table above, it’s clear that the benefit curve often follows an “inverted U” or “threshold-plateau” shape: before reaching the effective threshold, effects increase with dose, but beyond a certain plateau point, there are not only no additional benefits, but marginal costs (side effects, gastrointestinal burden, financial expense) rise sharply. This means that “finding your own optimal dose” matters far more than “taking as much as possible.” It is recommended to progressively test different doses during training (not on race day), recording subjective feelings, gastrointestinal responses, and power data to build your own dose profile. Remember: the laboratory average is a starting point, not the endpoint; each person’s body weight, metabolic rate, gut tolerance, and genetic background will cause the optimal dose to shift individually.

Differences Across Populations

The benefits of “caffeine supplementation” are not equal for everyone. Age, sex, training status, body composition, and genetic background all significantly modulate individual response magnitude. Ignoring these differences and applying a one-size-fits-all recommendation is one of the most common mistakes in sports nutrition.

| Population Dimension | Response Characteristics | Practical Recommendations |

|—|—|—|

| Beginners vs. Advanced | Advanced athletes have more mature physiological adaptations; responses are often more stable but with smaller marginal benefits | Beginners should start conservatively with low doses to build tolerance first |

| Male vs. Female | Differences in body weight, hormonal cycles, and sweat composition affect dosage and requirements | Females should individualize by body weight and pay attention to iron and energy availability |

| Young vs. Older | Older individuals often have reduced absorption efficiency and anabolic resistance | Older individuals may need higher doses or better timing |

| Body Size Differences | Body weight directly affects the absolute amount calculated per mg/kg or g/kg | Always convert to a dose corresponding to personal body weight; avoid copying general rules |

When interpreting “individual differences,” one must also be wary of a common statistical trap: studies mostly report “group average responses,” but beneath the average often lies enormous individual variability. In the same intervention, there may be strong responders, non-responders, and even negative responders. This is why even when a study shows “average effectiveness,” you still need to confirm through your own testing which category you fall into. The recommended approach is to conduct personalized A/B testing: in two training sessions with as similar conditions as possible, adopt and then not adopt the strategy respectively, comparing power, heart rate, and subjective feelings, repeating several times before drawing conclusions. This empirical spirit of “using yourself as the sample” is the necessary path to translating population science into personal prescriptions.

Taking Taiwan’s common amateur endurance population as an example, many are middle-aged riders over 35 who train around work commitments. This population simultaneously faces reduced recovery speed, sleep deprivation, and time pressure, so the “return on investment” of nutritional strategies is often higher than for younger elites—meaning correct nutritional intervention can yield relatively greater room for improvement. Female athletes need to pay special attention to the effects of the menstrual cycle on metabolism and requirements, as well as whether energy availability is sufficient, avoiding the trap of low energy availability (LEA) in the pursuit of being lighter. After understanding population differences, you’ll realize: truly professional nutritional advice is always an individualized prescription that “varies by person,” not a one-size-fits-all slogan.

Practical Training Application

Theory must ultimately be implemented on the training plan and the race course. Below is a practical framework for translating “caffeine supplementation” into concrete training and race operations:

• Pre-race testing principle: All nutritional strategies must first be rehearsed in training; “never try anything new on race day” is an iron rule. Gut tolerance to new fueling products takes time to build.

• Periodization mindset: Align nutritional strategies with training cycles—the base phase can emphasize adaptation-oriented strategies, while the pre-season shifts to performance-oriented fueling optimization.

• Progressive introduction: Start with low doses and low frequency, gradually adjusting based on bodily responses to build a personalized dose and timing profile.

• Data tracking: Combine power meter, heart rate, rating of perceived exertion (RPE), and gastrointestinal comfort records to objectively evaluate whether the intervention is truly effective.

• Holistic context: Nutrition is one component of training, sleep, recovery, and psychology; no single supplement can compensate for sleep deprivation or flawed training design.

Using a one-week training schedule as an example, it is recommended to rehearse different fueling scenarios during key midweek high-intensity sessions (such as threshold intervals, repeated climbs) and weekend long rides: high-intensity days emphasize rapid energy supply and central activation, while long-distance days emphasize sustained energy supply, gut tolerance, and recovery. Through repeated rehearsal, your body can execute the optimal fueling rhythm “automatically” on race day, leaving mental resources for pacing and tactical decisions. Remember, the goal of a nutritional strategy is not theoretical perfection, but reliability and stability under real race-course fatigue, heat, and pressure.

The most common mistake people make when executing a nutrition plan is “being serious only on race day while eating carelessly during regular training.” This is precisely putting the cart before the horse: regular training is the ideal laboratory for building gut tolerance, testing doses, and cultivating fueling rhythm. If you want to successfully execute an 80 g/hour carbohydrate fueling plan on race day, you must rehearse it repeatedly in training until your body is accustomed to it; if you want to rely on a certain supplement, you must confirm in training that it is genuinely effective for you and free of side effects. It is recommended to integrate a nutrition log with your training log, recording fueling content, intake timing, gastrointestinal responses, and performance data for each key session. After weeks to months of accumulation, the value of this personalized database will far exceed any generic nutrition guide. Additionally, don’t overlook the often-underestimated “post-training recovery fueling”—the quality of recovery between consecutive training days often determines whether you can steadily accumulate training volume without injury, and training volume is the most fundamental engine of long-term progress. Treat nutrition as part of training and take it seriously, rather than as an afterthought you scramble for before races—your improvement curve will be noticeably different.

Taiwan-Specific Application

Taiwan’s unique climate, terrain, and race culture add localization considerations to the application of “caffeine supplementation.” Taiwan’s summer heat and humidity often push perceived temperatures above 35°C, with sweat rates and fluid/electrolyte losses far exceeding the research conditions of temperate countries. This means that hydration and fueling recommendations from foreign literature often need to be “revised upward.” In events like the West Route to Wuling, which climbs from sea level to 3,275 meters, the appetite suppression of high altitude, low temperatures, and prolonged exercise pose a severe test for energy planning.

Regarding local fueling options, Taiwan’s abundant bananas, sweet potatoes, pineapples, sports drinks, and convenience-store ready-to-eat foods can all be incorporated into fueling strategies; the extremely high density of convenience stores also makes mid-ride refueling on long rides relatively easy. It is recommended that Taiwanese riders planning classic routes such as Sun Moon Lake, Wuling, Beiyi, Buyanting, and the East Route pre-identify fueling points along the way, and strengthen sodium and fluid supplementation in response to Taiwan’s humid, hot environment. Athletes in the Taroko Marathon, Taipei Marathon, and various local triathlon events should likewise incorporate the aforementioned local climate factors into their personalized nutrition plans to perform at their best under subtropical conditions.

Common Myth Debunking

Myth: The myth is that “you must drink very strong coffee before exercise.” In fact, doses above 9 mg/kg not only provide no additional benefit but may actually impair performance through anxiety and elevated heart rate. A more precise approach is to calculate 3–6 mg/kg based on body weight.

The reason such myths are so widespread is often that they “sound reasonable,” are easy to pass along by word of mouth, or are amplified by marketing rhetoric. Yet the value of science lies precisely in testing intuition with rigorous evidence: many seemingly obvious notions fail to hold up under scrutiny in randomized controlled trials. The field of sports nutrition is especially rife with oversimplified “panacea” style marketing that compresses complex dosing, timing, and individual differences into a single slogan. The next time you hear a dogmatic nutritional recommendation, it’s worth asking: “What is the level of evidence for this claim? Who is the target population? Are the dose and timing clearly specified?” Cultivating this evidence-based critical thinking is more valuable than memorizing any single conclusion, and it is a key step for amateur athletes moving toward scientific training.

Conclusion

“Caffeine supplementation” is a topic in sports nutrition that combines both theoretical depth and practical value. From the academic evidence reviewed in this article, its benefits are real, but it is by no means an unconditional panacea—the key lies in correct dosing, appropriate timing, individualized adjustment, and synergy with overall training, recovery, and sleep. For endurance sports enthusiasts in Taiwan, while mastering the scientific principles, it is equally important to combine local climate, terrain, and race characteristics to translate general rules into a personalized prescription that suits you. May every rider sweating on Wuling, in the valley, or on the round-island route break through their limits through science-based nutritional strategies and enjoy the pure joy that sport brings. Before you next step onto the race course, don’t forget—your fuel bottle holds not just water and sugar, but an entire body of validated sports science.

Related Reading

• The Science of Caffeine: Optimal Dosage and Timing for Endurance Sports
• Synergistic Benefits of Pre-Exercise Carbohydrate and Caffeine: A Quantitative Study of Additive Effects
• Caffeine Application in Cycling: Intake Timing and Dosage
• The Performance-Enhancing Science of Caffeine: A Guide to Optimal Intake Timing and Dosage for Cyclists