Endurance Fueling

Endurance exercise is limited largely by carbohydrate (glycogen) availability (see glycogen); running low forces a drop in pace ("the wall"). Fueling spans three phases:

• Daily base: match carbohydrate to training load — 5–7 g/kg/day for ~1 h/day, 6–10 g/kg/day for 1–3 h/day, and 8–12 g/kg/day for extreme volume (see carbohydrates). Chronically under-fueling carbohydrate undermines training quality.
• During exercise: for efforts over ~60 minutes, take in carbohydrate to spare glycogen and maintain output — ~30–60 g/h for 1–2.5 h, and up to ~90 g/h beyond that using a glucose-fructose blend (~2:1) that exceeds the single-sugar ~60 g/h absorption ceiling (see carbohydrate-timing). Pair with a fluid and sodium plan (see exercise-hydration-strategy).
• Before/after: top off glycogen with a pre-event carbohydrate meal, consider carbohydrate loading for events over ~90 min (see carb-loading), and refuel promptly after.

Gut training matters: the ability to absorb 60–90 g/h is trainable — practice race-day intake in workouts to avoid GI distress. Protein needs remain elevated for endurance athletes (~1.2–2.0 g/kg/day) for repair and adaptation, but carbohydrate is the performance lever during the event.

• Daily carbohydrate: 5–7 (1 h), 6–10 (1–3 h), 8–12 (extreme) g/kg/day.
• During >60 min: ~30–60 g carb/h; up to ~90 g/h via glucose:fructose (~2:1).
• Single-sugar absorption caps ~60 g/h; train the gut to tolerate more.
• Pair carbohydrate with fluid and sodium during long efforts.
• Endurance protein ~1.2–2.0 g/kg/day; carbohydrate is the in-race lever.

• glycogen / carbohydrates — the limiting fuel and daily needs.
• carbohydrate-timing / carb-loading — timing and pre-event maximization.
• exercise-hydration-strategy — fluids and sodium during events.
• long-slow-distance — training context for fueling.