Questions: Sports Nutrition: Fueling Performance and Recovery

Question 1

A competitive powerlifter wants to maximize performance in an upcoming meet consisting of three maximal lifts over about two hours. Their coach recommends carbohydrate loading in the week before. Is this advice appropriate?

• A. Yes — carbohydrate loading maximizes glycogen stores, which always improves athletic performance regardless of sport
• B. Yes — maximal lifts heavily recruit fast-twitch fibers that are entirely glycogen-dependent, so supersaturating glycogen is critical
• C. No — carbohydrate loading primarily benefits prolonged endurance activities lasting more than 90 minutes; powerlifting's maximal efforts rely on the phosphocreatine system and are not limited by glycogen availability
• D. No — excess stored glycogen draws water into muscle cells, increasing body weight and reducing the power-to-weight ratio in strength sports

Answer: (C)

Carbohydrate loading extends the time before glycogen depletion causes fatigue — a benefit only relevant when glycogen is the performance-limiting fuel. This occurs during prolonged moderate-to-high intensity exercise lasting more than 90 minutes (marathons, long triathlons). Maximal powerlifting efforts last seconds and are fueled primarily by the phosphocreatine (PCr) system; glycogen is not the limiting factor because normal glycogen stores are more than adequate for short maximal efforts. The coach is applying a principle valid for endurance sport to a context where it provides no performance benefit.

Question 2

An athlete finishes a 2-hour training session that significantly depleted muscle glycogen and plans to train again in 8 hours. What post-exercise nutrition strategy best supports glycogen resynthesis?

• A. Wait 3–4 hours before eating; the muscles need time to recover before they can store glycogen effectively
• B. Consume carbohydrates as soon as possible after exercise (within 30–60 minutes) when GLUT4 transporter activity is highest and glycogen synthesis rate is at its peak
• C. Prioritize protein intake immediately post-exercise; glycogen synthesis does not reach meaningful rates until several hours later
• D. Consume fat and protein only; post-exercise insulin spikes from carbohydrates impair the hormonal recovery environment

Answer: (B)

Muscle glycogen synthesis is fastest in the first 30–60 minutes post-exercise because muscle contractions activate GLUT4 glucose transporters via an insulin-independent pathway, maximizing glucose uptake. Post-exercise insulin sensitivity is also elevated. Delaying carbohydrate intake even 2 hours can reduce early glycogen resynthesis rates by approximately 50%. When the next training session is only 8 hours away, this window is critical — normal meal timing may not provide enough time for full glycogen restoration without prioritizing early post-exercise carbohydrate intake.

Question 3

Combining glucose and fructose in sports drinks can allow higher carbohydrate delivery rates than glucose alone because the two sugars use different intestinal absorption transporters that can operate simultaneously without saturating each other.

• T. True
• F. False

Answer: True

The intestinal glucose transporter SGLT1 saturates at roughly 60 g/hour. Fructose uses a separate transporter GLUT5 with its own capacity. By supplying both, total intestinal carbohydrate absorption can reach 90–120 g/hour — well above what either transporter alone can handle. This is why sports products designed for high-intensity prolonged efforts (more than 2–3 hours) combine multiple carbohydrate sources, and why fructose-containing mixtures outperform glucose alone in endurance time trials despite fructose's slower pathway to muscular energy.

Question 4

Creatine supplementation primarily benefits endurance athletes because it increases the phosphocreatine pool, allowing sustained aerobic energy production during long events.

• T. True
• F. False

Answer: False

Creatine's benefit is specifically tied to the phosphocreatine (PCr) system, which provides rapid ATP for high-intensity efforts lasting roughly 5–30 seconds — explosive power movements, sprints, heavy resistance lifts. The PCr system depletes quickly and must recharge during rest; it is not the primary fuel for prolonged endurance efforts, which rely on aerobic oxidative metabolism. Creatine supplementation provides meaningful performance benefit for strength and power athletes, not for endurance sports where the PCr system is rarely the limiting factor. Context-specificity — matching the supplement to the energy system it supports — is a core principle of evidence-based sports nutrition.

Question 5

Why is leucine specifically highlighted in post-exercise protein recommendations, rather than just emphasizing total protein quantity?

Model answer: Leucine is an essential branched-chain amino acid that acts as a signaling molecule, not only a substrate for protein synthesis. It specifically activates the mTOR (mechanistic target of rapamycin) signaling pathway, which is the primary initiator of muscle protein synthesis. Two protein sources with identical total protein content but different leucine concentrations will produce different magnitudes of muscle protein synthesis response — the higher-leucine source triggers a larger anabolic signal. This is why protein quality (leucine content, found abundantly in whey, eggs, and meat) matters as much as quantity. The practical implication is that 0.25–0.4 g/kg of high-quality, leucine-rich protein produces a better post-exercise response than a larger amount of low-leucine protein.

This also explains why the practical recommendation emphasizes food quality over supplement use: whole-food protein sources with high leucine content (eggs, dairy, lean meat) achieve the same or greater mTOR stimulation as protein isolates, provided the leucine threshold is met.