New study: carbs do not just stop the bonk

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Most riders think about fuelling as insurance against bonking. Eat enough and you avoid the wall. True, but it undersells what fuel is actually doing late in a ride, and a new study makes the bigger point clearly.

Researchers had trained cyclists ride steadily for three hours, then tested their critical power, the rough ceiling for what they can hold for a sustained hard effort. They did this three times, once on water only, once taking 60 grams of carbohydrate an hour, and once at 120 grams an hour. The question was how much that late-ride ceiling fell, and whether fuelling protected it.

The water-only ride cost them about 15 per cent of their critical power. At 60 grams an hour the drop was roughly halved to about 7 per cent. At 120 grams an hour it fell to about 4 per cent. More fuel, more of your hard-effort ceiling preserved at hour three, in a clear dose-dependent line. That is not just bonk avoidance. That is your ability to still go hard late, bought with what you put in the bottle. Fuelling is a durability lever, not only a safety net.

There is an honest limit worth keeping in view, and it is the part that keeps this useful rather than hype. Carbohydrate protected sustainable power, but it did nothing for W prime, your finite store for sprints and repeated surges. That faded the same amount no matter how much they ate. So fuel keeps you strong late. It does not refill your matchbook. Pacing and match conservation still decide a lot. And even 120 grams an hour did not fully stop the decline, because durability is built from more than fuel.

What to do with this

If you race or do hard efforts late: this is your case for fuelling high. Work towards 90 to 120 grams an hour on long, hard days, but build the gut up to it in training first, because race day is the wrong place to find your limit. Do not expect it to save your sprint, only your sustained power.

If you ride big events and gran fondos: the late-ride payoff here is exactly your second half. Practise your event fuelling on your long rides, not just the riding. A gut that handles 80 to 100 grams an hour is a trainable skill, and it changes how the last hour feels.

If your time is capped: you do not need to chase 120. The big win for you is going from under-fuelling to a reliable 60 to 80 grams an hour on your few long or hard sessions. Most of the durability benefit sits in that first move, without the gut risk. And remember the quieter lesson, the zones you set fresh do not hold when you are tired, so fuel your hard work or accept the number is flattering you.

Citation: Norte BR, Slinn MM, Johnson KO, Mahon E, Shepherd SO, Strauss JA, Louis JB. Graded Carbohydrate Ingestion up to 120 g·h⁻¹ Attenuates the Reduction in Critical Power Following 3 h of Moderate-Intensity Exercise in a Dose-Dependent Manner. Scandinavian Journal of Medicine & Science in Sports. 2026;36(6):e70326. doi:10.1111/sms.70326

On my mindVLamax, and sharpening a hunch about the gym

I have been chewing on an idea about strength work and aerobic performance, and I want to lay it out properly, because the first version in my head reached for the wrong mechanism. This is not the old story about strength and endurance training cancelling each other out. It is about VLamax, the metric Sebastian Weber and the INSCYD group have built so much of their thinking around.

VLamax is simply how fast your muscles can produce lactate, your glycolytic power. Your threshold, your FTP or critical power, is not set by your aerobic engine alone. It is set by your aerobic capacity and your VLamax together. A high VLamax drags your threshold down and makes you burn more carbohydrate at any given pace. For a sprinter, that is a weapon. For someone whose event is long and purely aerobic, it is a tax. Lower the VLamax and, all else equal, your threshold rises and you burn more fat. That is durability, in metabolic terms, and it ties straight back to the fuelling study above.

So where does the gym come in. The glycolytic machinery lives in your fast twitch fibres, and training that hammers those fibres in a glycolytic way, short maximal efforts, fatiguing high-rep sets, explosive repeats, can push VLamax up. For a purely aerobic rider chasing threshold, that can quietly pull against the goal. That is the real version of my hunch, and it holds up.

But here is the refinement, because the detail decides everything. It is not strength training as a category that raises VLamax. It is glycolytic stimulus. Heavy, low-rep, high-force lifting with long rests is largely a neural and structural stimulus with little glycolytic cost. So the smart move in a long aerobic build is usually not to abandon the gym. It is to strip out the glycolytic stimulus and the short max efforts, and keep the heavy, low-rep strength that does not lift VLamax. And mind the cost. A lower VLamax means less sprint and less punch. Ideal for a time trial or a long fondo. A poor trade for a crit. As always, it depends on the event.

Damian