Most sports nutrition advice in circulation is endurance advice. It was worked out on cyclists and runners, where fuel runs out and the answer is to add fuel. Applied to a 50-minute gym session it produces confident recommendations that the resistance-training literature does not support. Here is what changes between endurance work, lifting and interval training — and what stays the same.
The short version
- Carbohydrate needs scale with training load, from 3–5 g/kg/day for light work to 8–12 for extreme volumes.
- Carbs during lifting are unlikely to help in a fed state, in sessions up to 10 sets per muscle group.
- They do help long or fasted lifting — the pooled effect appears above 45 minutes and after fasts of 8 hours or more.
- Carbs during exercise do not build muscle. A 2026 meta-analysis found no effect on hypertrophy.
- Endurance is not a low-protein sport. One trial put the requirement at 1.83 g/kg/day on a hard training day.
- Caffeine works across modalities at 3–6 mg/kg, with the most consistent benefit in endurance.
Start with the daily number
Before any timing question, carbohydrate intake scales to how much you train. The joint Academy of Nutrition and Dietetics and ACSM position statement bands it:
| Training load | Example | Carbohydrate |
|---|---|---|
| Light | Low intensity or skill-based activity | 3–5 g/kg/day |
| Moderate | About 1 hour a day | 5–7 g/kg/day |
| High | 1–3 hours a day of moderate to high intensity | 6–10 g/kg/day |
| Very high | 4–5 hours or more a day | 8–12 g/kg/day |
Most people reading this are in the first two rows. The eye-catching numbers belong to athletes training several hours daily, and quoting them at a recreational lifter is the single most common error in this area.
Endurance: where the classic advice actually applies
This is the modality the research was built on, and the recommendations are specific:
| Duration | Carbohydrate during |
|---|---|
| 45 minutes or less | Not needed |
| 45–75 minutes | Small amounts, including a mouth rinse |
| 1–2.5 hours | 30–60 g per hour |
| 2.5–3 hours or more | Up to 90 g per hour, glucose–fructose mix |
The ceiling has a physical cause: glucose absorption “becomes saturated at a carbohydrate intake of around 60 g/h.” Adding fructose opens a second transport route and lifts oxidation rates by up to 75%, which in one trial translated into 8% more power output than glucose alone. Above 90 g/h, a 2025 review notes an intake rate greater than that “may not lead to additional performance improvements.”
Eating beforehand matters here too, and only here. A meta-analysis of 37 studies found feeding improved performance in exercise longer than 60 minutes — and produced an effect size of exactly zero under 60 minutes.
Lifting: the honest answer is “mostly no”
Resistance training does use glycogen — six sets of 12-rep leg extensions reduce stores by about 39%. That fact gets used to justify carbohydrate during lifting. The trials do not follow.
A systematic review of 49 studies found that acutely, “higher carbohydrate intake did not improve performance in 13 studies and enhanced performance in six studies.” Its practical conclusion is unusually direct: “Carbohydrate intake per se is unlikely to [benefit] strength training performance in a fed state in workouts consisting of up to 10 sets per muscle group.”
Where it does help is specific. The accompanying meta-analysis of 21 studies found the ergogenic effect on training volume appears “when sessions exceed 45 min and where the fast duration is ≥ 8 h.” A long, high-volume session first thing in the morning after an overnight fast is the case that benefits. A fed 40-minute session is not.
Two findings that close the argument. Carbohydrate intake does not appear to build more muscle: a 2026 meta-analysis of 11 studies found no significant effect on hypertrophy (SMD = 0.15, p = 0.23), with low certainty. And low glycogen does not appear to blunt the anabolic response: it “has not been found to significantly affect anabolic signaling or muscle protein synthesis after strength training.” Eat carbohydrate because it fuels your training week — not because a session will otherwise fail.
Intervals: short, but glycogen-dependent
High-intensity intervals are where the intuition “it’s only five minutes, fuel doesn’t matter” breaks down. A controlled one-legged study depleted glycogen in one leg and loaded the other in the same person — 177 against 593 mmol/kg — then tested both. In exercise lasting about five minutes, “time to task failure … was reduced by approximately 40%” in the depleted leg.
So starting intervals under-fuelled costs performance, even though the session is short. What it does not do is train you better. A review of low-carbohydrate training notes it “enhances the upregulation of mitochondrial enzymes” but delivers “no performance advantage” — which is why periodising it is framed as a maybe, not a method.
Protein: less modality-dependent than people think
The position stands do not split protein by sport. The ISSN gives one range for everyone exercising: 1.4–2.0 g/kg/day. The joint ACSM statement gives 1.2–2.0 g/kg/day.
The idea that endurance athletes need less protein is the misconception worth correcting. A study using indicator amino acid oxidation in endurance-trained adults after a 20 km run put the estimated average requirement at 1.65 g/kg/day and the recommended intake at 1.83 g/kg/day — with the authors noting the demand “is greater than their sedentary peers and current recommendations for athletes.”
The ISSN’s endurance-specific note is about arrangement rather than amount: roughly 0.25 g of protein per kg per hour of endurance exercise, with carbohydrate remaining the priority for performance.
Caffeine, by modality
The one supplement that works across all three. The ISSN position stand: “Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3–6 mg/kg body mass”, typically 60 minutes before, with benefits spanning muscular endurance, strength, sprinting, jumping and throwing.
Its ranking by modality: “Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use.” And the ceiling: very high doses around 9 mg/kg bring side effects without extra benefit. The FDA cites 400 mg a day as an amount not generally associated with negative effects in adults.
The whole thing in one table
| Endurance | Resistance training | Intervals | |
|---|---|---|---|
| Carbs during | Yes, by duration: 30–60 g/h past an hour | Generally no — unless over 45 min or fasted 8+ h | Not during; arrive fuelled |
| Eating beforehand | Helps beyond 60 min; no effect under | Matters mainly after a long fast | Start with glycogen available |
| Protein | 1.4–2.0 g/kg/day; possibly up to 1.83 on hard days | 1.4–2.0 g/kg/day | 1.4–2.0 g/kg/day |
| Caffeine | Most consistent benefit | Real but smaller | 3–5 mg/kg used in trials |
FAQ
Do I need an intra-workout carb drink for lifting?
Almost certainly not. The systematic review found carbohydrate unlikely to help strength performance in a fed state in sessions up to ten sets per muscle group. Long sessions after an overnight fast are the exception.
Will carbs during training help me build muscle?
No effect was found in the pooled hypertrophy data — 11 studies, SMD 0.15, p = 0.23, low certainty.
Should I train fasted?
For sessions under an hour it made no measurable difference to performance. Beyond an hour, eating beforehand helped. For lifting, a long overnight fast is where carbohydrate showed a benefit.
Do endurance athletes need less protein?
No. The position stands give one range for all exercising people, and a study in endurance-trained adults after a hard run put the recommended intake at 1.83 g/kg/day.
How much caffeine, and when?
3–6 mg per kg of body mass, most commonly 60 minutes before. Endurance shows the most consistent benefit; doses around 9 mg/kg add side effects without extra performance.
Where this fits
The principles behind these numbers are in nutrient timing, and what to do afterwards is in recovery nutrition. Claims about protein windows, per-meal ceilings and fasted cardio are checked in sports nutrition myths, and stomach trouble during long sessions in the gut and athletic performance.
Every figure here is linked to its source in the text: the joint Academy of Nutrition and Dietetics / Dietitians of Canada / ACSM position statement, International Society of Sports Nutrition position stands, the FDA, and peer-reviewed systematic reviews and trials in Sports Medicine, Nutrients, Frontiers in Physiology, PLOS ONE and the Scandinavian Journal of Medicine & Science in Sports. Checked against those sources on 2 September 2026. Educational information, not medical advice — see our medical disclaimer.
This content is for educational purposes only and is not medical advice. Always consult a qualified healthcare professional for personalised guidance.
