There’s plenty of research showing that consuming carbohydrates during exercise — aka fueling — improves endurance performance. Fueling keeps blood glucose levels high, spares liver glycogen, and may help spare muscle glycogen. The result? Athletes can ride longer and harder.
But how should you fuel?
- Same carbohydrate amounts, consistently throughout?
- Higher amounts at the start, lower at the end? (Front-loaded)
- Lower at the start, higher at the end? (Back-loaded)
A new study by Dr. Tim Podlogar and colleagues tested these fueling strategies — and the results might surprise you.
Want the full details? In the Nduranz podcast, Dr. Podlogar breaks down the study and what it means. Listen now.
The Test: Mimicking Race Day
To test the fueling strategies, the research team recruited trained cyclists. The cyclists completed a demanding protocol designed to mimic race conditions: a 3-hour ride, followed by a 15-minute all-out performance test, and a final sprint to exhaustion.
The athletes performed the entire test three times. During each test, the cyclists consumed the same total carbohydrates: 293 grams (for an average of 90 grams/hour) administered in 15-minute intervals during the 3-hour ride.
The twist was in the distribution:
- DEC (Decreasing): Larger doses at the onset, gradually tapering off. (The Front-Loaded Approach)
- CON (Constant): The same dose throughout. (The Consistent Approach)
- INC (Increasing): Smaller doses at the onset, gradually increasing. (The Back-Loaded Approach)
The Hypothesis: Why Increasing Was Expected to Win
Going into the study, Dr. Podlogar and his colleagues hypothesized that the increasing strategy would be the best fueling strategy for performance. Their reasoning was rooted in three key physiological principles:
1. Optimizing Late-Stage Fueling
During the onset of exercise, the body primarily relies on stored glycogen for fuel. These stores gradually decrease as exercise continues — and the body starts using blood glucose faster. At the same time, the body also increases the rate at which it oxidizes ingested fuel.
Thus, the researchers believed that the INC fuel strategy would provide the highest fuel dose exactly when the muscle's reliance on plasma glucose was greatest and the body was best equipped to oxidize the fuel.
2. Higher Fat Oxidation for Glycogen Sparing
Some research suggests that consuming large amounts of fuel at the onset of exercise may slow fat oxidation, without further sparing muscle glycogen (possibly because of an increase in insulin concentrations). The researchers thus hypothesized that the INC strategy, by starting with smaller doses, would allow fat oxidation to remain high for longer, thereby preserving precious glycogen stores and delaying fatigue.
3. Gut Comfort
The body's rate of carbohydrate absorption and utilization increases gradually during exercise. The researchers reasoned that a gradual increase in intake of fuel would avoid exceeding the gut’s absorptive capacity early on, thus reducing the risk of uncomfortable symptoms like nausea or fullness.
The Surprising Results
Contrary to what they expected, the researchers found that all fuel distribution strategies provided similar results.
Performance
No clear differences during the 15-minute all-out performance (15AO) test or max sprint to exhaustion test (TTE). Whether carbs were front-loaded, spread evenly, or back-loaded, cyclists performed about the same.
CHO and Fat Oxidation
- DEC showed slightly higher carbohydrate oxidation and slightly lower fat oxidation — but not enough to boost performance.
- INC didn’t improve fat oxidation or spare glycogen as expected.
Heart Rate and Rate of Perceived Exertion
- Heart rate was mostly unaffected, though there were slight slope differences between CON and INC, as well as DEC and INC.
- Ratings of Perceived Exertion (RPE) were similar, with a slight trend toward lower RPE in INC compared to CON, but INC had a higher slope than CON.
Gut Comfort
The strategies didn't necessarily reduce discomfort — though they slightly shifted when the discomfort occurred. Not surprisingly, fullness and nausea were highest when dosages were at their highest. There was no major difference in cramping.
What This Means for Your Ride
The study's simple yet profound conclusion: regular, sufficient fueling is more important than minute-by-minute fuel distribution.
This is great news for cyclists! Adhering to strict fueling schedules during races is often impossible — you can't exactly grab a gel during an intense breakaway or on a steep descent.
So, for most cyclists, a simple approach is best:
- Focus on Total Carbs First: Aim for your target grams per hour (like the 90 g/h tested here). Hitting your total number is the real key.
- Start with Slightly Lower Amounts: Dr. Podlogar still recommends using smaller doses of fuel at the onset of exercise to reduce GI discomfort and allow for better fat oxidation.
- Then Aim for Consistent Intake is Safest: Spreading carbs consistently throughout a ride works reliably and is the simplest approach.
- Inconsistent Intake Isn't a Disaster: If race conditions or logistics force you to front-load (DEC) or back-load (INC) your carbs, it probably won't hurt your performance, as long as the total intake is sufficient.
- Listen to Your Gut: If you're prone to nausea or cramping, remember that heavy carbs late in the ride (INC) can cause late-stage discomfort, while heavy carbs early (DEC) can cause early discomfort. Gut training can help with this.
The old advice holds true: hit your target carbs, don’t overthink the timing, and listen to your gut!
Want personalized advice? Use our Fueling Calculator to see how many carbohydrates per hour you should target.
Don't forget to listen to the Nduranz podcast to hear Dr. Podlogar's breakdown of the study.