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High-Carbohydrate Fueling for High-Intensity Work

  • Owner: Nutrition
  • Date added: 2026-04-10
  • Last reviewed: 2026-04-10
  • Review status: Current — authored from proposal stub and domain knowledge without full paper access

Source

  • Title: A step towards personalized sports nutrition: carbohydrate intake during exercise
  • Author(s): Jeukendrup, A.E.
  • Year: 2014
  • Type: Review (Sports Medicine, 44(Suppl 1), 25–33)

Evidence class

Narrative review by a leading researcher in exercise nutrition, supported by extensive primary research including metabolic tracer studies, performance trials, and applied field research in endurance and team sports. The evidence base for carbohydrate dose-response during exercise is strong.

Summary

Intestinal glucose transporter saturation limits single-source carbohydrate absorption to approximately 60 g/hour. Using multiple-transporter carbohydrate blends (glucose:fructose at approximately 2:1 ratio) enables absorption rates up to 90–120 g/hour with gut training. Higher carbohydrate availability during exercise improves performance in events lasting longer than approximately 60 minutes. The relationship is dose-dependent up to the absorption ceiling, but gastrointestinal tolerance is the practical limiter in most athletes.

Key findings

  • Single-source carbohydrate (glucose or maltodextrin only) is limited to ~60 g/hour absorption regardless of intake.
  • Glucose:fructose blends (2:1 ratio) unlock a second absorption pathway and enable 90–120 g/hour in trained guts.
  • Gut training — progressive exposure to higher intakes during training — is essential. Attempting race-day intake without training the gut causes GI distress.
  • The performance benefit is real and measurable: improved time-trial performance, sustained power output, reduced RPE at matched intensity, and delayed glycogen depletion.
  • The benefit scales with exercise duration and intensity. For sessions under 60 minutes, mouth rinsing with carbohydrate may be sufficient. For 1–2.5 hours, intake of 60–90 g/hour is recommended. For events beyond 2.5 hours, 90+ g/hour is the target.
  • Individual variation in tolerance and preference is large. Personalisation matters more than following population averages.

Application

  • Current block (April rebuild): On-bike fueling targets are already set in the detailed training block:
    • Easy endurance sessions >90 min: 60 g/hour
    • Steady endurance / tempo-supported: 75 g/hour
    • Long endurance and threshold sessions: 90 g/hour These targets are appropriate for the current training phase and align with the research.
  • Gut training: The current block should serve as a gut-training period. Sidney should practice hitting the 60–75 g/hour targets consistently so that higher rates (90+ g/hour) are tolerable when needed during CX-specific build phases and race season.
  • Race-day application: CX races are approximately 50–60 minutes. Pre-race carbohydrate loading and pre-race meal timing are more important than during-race intake at this duration. During the race, mouth rinsing or small sips of high-concentration carbohydrate drink may be beneficial, but the main fueling opportunity is before the start.
  • Post-ride recovery: The current block already specifies recovery protein (25–30 g) and carbohydrate targets. This should remain standard practice.
  • Sidney's food preferences: Medjool dates are a reasonable on-bike carbohydrate source for endurance rides (primarily glucose/fructose, ~20 g carb per date). Peanut butter is better off-bike. For high-intensity interval sessions, engineered carbohydrate products (gels, drink mix) are preferable for precise dosing and absorption speed.

Caveats

  • CX race duration (~50 min) is at the lower end where during-exercise carbohydrate provides measurable performance benefit. Pre-race nutrition strategy matters more for CX than during-race fueling.
  • The research population is primarily male endurance athletes. Female-specific modifiers (menstrual cycle, hormonal contraception, relative energy availability) may affect optimal intake rates and should be tracked.
  • Hashimoto's thyroiditis may affect gut motility and absorption. GI symptoms that appear disproportionate to intake volume could reflect thyroid-related gut dysfunction rather than simple overloading.
  • High carbohydrate intake during exercise does not compensate for chronic low energy availability. The daily energy budget must be adequate first.

Relevance to Sidney

Sidney is a CX specialist in a rebuild phase. The current training block already sets appropriate on-bike fueling targets. The primary nutrition opportunity in this block is building reliable gut-training habits at 60–75 g/hour so that higher rates are available later in the season.

For race-day CX nutrition, the focus should shift to pre-race meal timing and composition rather than during-race intake, given the 50–60 minute race duration. This will become operationally important when race preparation begins (Phase 5–6 of the season plan).

Sidney's preference for Medjool dates should be supported on easier training days and supplemented with engineered products during higher-intensity or higher-demand sessions where absorption precision matters.

Decision impact

  • Current block fueling targets — already aligned. No change needed to the rolling 7-day or training block nutrition prescriptions.
  • skills/morning-plan/SKILL.md — fueling section should continue specifying concrete gram targets for pre-ride and during-ride intake rather than vague guidance. This is already implemented.
  • Future race-day preparation — when Phase 5–6 is planned, this entry should inform the pre-race nutrition protocol.
  • Gut training tracking — the nutrition agent should monitor Sidney's tolerance at current targets and note any GI issues as data for future intake decisions.