Why carbohydrates matter for exercise
Carbohydrates are stored as glycogen in your muscles and liver. During moderate-to-high intensity exercise (above ~65% VO2 max), glycogen is the primary fuel source. When glycogen runs low, performance drops noticeably — this is commonly called "hitting the wall" in endurance sport.
For strength training, glycogen powers the anaerobic energy system (ATP-PCr and glycolysis) used during explosive movements. Even a single session of resistance training can deplete 25–40% of local muscle glycogen. Starting a workout with depleted glycogen stores leads to reduced output, more perceived effort, and less training volume.
The case for pre-workout carbs
Consuming carbohydrates 1–3 hours before training tops up liver and muscle glycogen, supporting sustained performance. Research consistently shows that pre-exercise carbohydrate feeding improves endurance, delays fatigue, and can increase total training volume in resistance sessions.
The ideal pre-workout carbohydrate source is moderate-to-low glycaemic index to avoid a blood sugar spike and crash. Good options include oats, rice, sweet potato, banana, or wholegrain bread 1–2 hours before training. Quantity depends on training duration: for sessions under 60 minutes, 30–50g of carbs is sufficient. For endurance sessions over 90 minutes, aim for 1–4g per kg body weight in the 1–4 hours before.
The case for post-workout carbs
After exercise, muscles are primed to absorb glucose for glycogen resynthesis. Consuming carbohydrates in the 30–120 minutes post-workout accelerates this replenishment. This matters most if you train twice per day or have another session within 8 hours.
Post-workout, pairing carbohydrates with protein (in a roughly 3:1 or 4:1 carb-to-protein ratio) appears to enhance glycogen resynthesis compared to carbs alone. A common practical approach: a meal containing 40–80g carbs and 25–40g protein within 1–2 hours of finishing training.
What matters most: total daily intake
For recreational exercisers training 3–5 days per week, research consistently shows that total daily carbohydrate intake has a far larger effect on performance and body composition than timing. A 2013 meta-analysis by Schoenfeld and Aragon found that the "anabolic window" around exercise is much wider than previously believed — hours, not minutes.
If you are not hitting your daily carbohydrate target, obsessing over whether to eat them before or after training is counterproductive. Hit your total target first, then optimise timing as a secondary concern.
Practical recommendations by goal
| Goal | Pre-workout | Post-workout |
|---|---|---|
| Fat loss | Small carb meal 1–2h before | Protein priority; carbs from daily allowance |
| Muscle gain | Moderate carbs 1–2h before | Protein + carbs within 2h |
| Endurance performance | 1–4g/kg carbs 1–4h before | High-GI carbs + protein immediately after |