Sports Nutrition Explained: Carbohydrates, Protein, and Ergogenics

Fuel Choices Define Training Outcomes

Elite marathon runners consume approximately 120–150 grams of carbohydrate per hour during competition — a rate that requires practiced gut training to absorb without gastrointestinal distress. Tour de France cyclists burn 7,000–8,000 kilocalories daily across three-week stages, requiring nutrition plans as precisely engineered as their training schedules. Sports nutrition is not supplementation strategy bolted onto a generic diet; it is periodized alongside training to match fuel availability with session demands and recovery targets.

Carbohydrate Periodization: Train Low, Sleep Low, Compete High

Carbohydrate periodization deliberately matches carbohydrate availability to the demands of individual training sessions, rather than maintaining uniform high-carbohydrate intake throughout a training cycle. The framework rests on evidence that training with reduced glycogen availability — "training low" — amplifies molecular adaptations to aerobic training, including increased mitochondrial biogenesis, elevated fat oxidation capacity, and upregulation of glucose transporters (GLUT4).

Train Low: Sessions performed with reduced muscle glycogen. This is achieved by performing a morning session before breakfast (fasted training), by scheduling two training sessions the same day without carbohydrate intake between them (same-day doubles protocol), or by restricting carbohydrate intake in the hours before a lower-intensity training session. Key finding: low-glycogen training enhances the AMPK-PGC-1α signaling cascade that drives mitochondrial adaptation. However, performance during the low-glycogen session is reduced — this strategy applies to low-intensity training sessions, not high-quality speed or interval work.

Sleep Low: An extension developed by Jeppe Kiilerich and colleagues at the University of Copenhagen. Athletes complete an evening glycogen-depleting session, consume no carbohydrates overnight, and complete a morning fasted training session before breakfast. This extends the low-glycogen exposure window to 10–12 hours, amplifying overnight signaling without sacrificing daytime session quality.

Compete High: On competition days and high-quality training sessions (intervals, time trials, speed work), full glycogen stores are essential. Pre-event carbohydrate loading (8–10 g/kg over 24–36 hours before events lasting >90 minutes) maximizes muscle glycogen. During events lasting >75 minutes, 60–90 g/hour carbohydrate ingestion (glucose + fructose blend in 2:1 ratio to exploit dual transporter capacity) sustains performance.

• The train-low strategy applies to 20–30% of weekly sessions in elite endurance training, not all sessions
• High-quality sessions (intervals, threshold, race-pace) are always performed with adequate carbohydrate availability
• Train-low adaptations require 4–8 weeks to manifest measurable improvements in fat oxidation capacity
• Sleep-low protocols increase 24-hour fat oxidation by 13–17% compared to carbohydrate-replete controls in controlled studies

Protein: The Morton 2018 Ceiling

The 2018 meta-analysis by Robert Morton and colleagues (British Journal of Sports Medicine, analyzing 49 randomized controlled trials, n=1,863) established the evidence-based protein ceiling for resistance training-induced muscle growth at 1.62 g/kg/day. Beyond this threshold, additional protein intake produced no statistically significant additional gains in fat-free mass. The 95% confidence interval upper bound was 2.2 g/kg/day, acknowledging that individual variation means some people may benefit from intakes up to that level.

Creatine: Dosing and Mechanism

Creatine monohydrate is the most extensively researched ergogenic supplement in sports science, with over 500 published studies. Creatine is stored in muscle as phosphocreatine (PCr), which donates a phosphate group to regenerate ATP during high-intensity, short-duration efforts (sprinting, heavy lifting, repeated explosive actions lasting <10 seconds). Supplementation increases muscle PCr stores by approximately 20% above natural levels, extending the ATP resynthesis buffer during maximal efforts.

Two dosing protocols are established:

• Loading protocol: 20 g/day (divided into 4 × 5 g doses) for 5–7 days, followed by 3–5 g/day maintenance. This saturates muscle stores rapidly within one week.
• Gradual loading: 3 g/day consistently for 4 weeks achieves equivalent muscle saturation without the loading phase gastrointestinal side effects (bloating, cramping in sensitive individuals). This is the pragmatic long-term maintenance dose.

Average performance benefits from creatine supplementation in high-intensity activities: 5–15% improvement in maximum work during repeated sprint sets, approximately 1–2% improvement in single maximal effort. Effects are greatest for activities relying heavily on the phosphocreatine energy system (<30 seconds). Long-term creatine use (up to 5 years) has no documented adverse health effects in healthy adults. Vegetarians and vegans show larger responses due to lower baseline dietary creatine intake.

Caffeine: The Most Used Ergogenic Aid

Caffeine is the world's most widely consumed psychoactive substance and one of the most robustly supported ergogenic aids in sports science. The International Society of Sports Nutrition position stand identifies caffeine as effective for improving endurance performance, high-intensity exercise, resistance training volume, and cognitive function during sport.

Mechanism: caffeine is an adenosine receptor antagonist. Adenosine accumulates during exercise and causes perceived fatigue by binding A1 and A2a receptors. Caffeine competitively blocks these receptors, reducing perceived exertion (RPE) at the same absolute intensity. Secondary mechanisms include enhanced calcium release from the sarcoplasmic reticulum (improving muscle contractility) and increased epinephrine release.

Dose-response evidence: the ergogenic window is 3–6 mg/kg body weight, consumed 30–60 minutes before exercise. Above 6 mg/kg, adverse effects (tremor, tachycardia, gastrointestinal distress, anxiety) increase without proportional performance benefit. For a 70 kg athlete, the optimal dose is 210–420 mg — equivalent to 2–4 standard espresso shots.

Caffeine tolerance from daily use reduces but does not eliminate the ergogenic effect. A 7-day washout period before competition maximizes the acute response for caffeine-habituated athletes, though complete abstinence is not required — the ergogenic effect persists in habitual users, just at a reduced magnitude compared to naïve responders.