CarbMax

Definition

“CarbMax” is the power range in which the body oxidises the largest amount of carbohydrate per hour under load and therefore needs to have it supplied. The term was coined by INSCYD and has since become established in performance diagnostics. As a rule of thumb the range is quoted as 60 to 90 g of carbohydrate per hour.

Unlike FatMax, CarbMax does not describe the peak of a substrate curve but a corridor. It marks the intensity from which energy provision relies almost entirely on glycogen and exogenous carbohydrate.

Why it matters

Training or racing in the CarbMax range burns carbohydrate faster than the gut can absorb it. Glycogen stores of roughly 400 to 600 g last two to three hours at 90 g/h and above. After that, the fuelling strategy decides between performance and collapse.

For race planning in endurance sport the range is therefore central. It tells you how much to eat, how long an intensity is sustainable at all and whether a planned race pace matches metabolic reality.

The upper limit is highly individual, however. Trained guts demonstrably process 100 to 120 g/h today, which is why the classic 60 to 90 g/h definition will most likely need revising.

How obseed measures it

obseed does not compute CarbMax from field tests or an estimated FTP. The range comes from metabolic diagnostics in which spiroergometry determines substrate use per stage. Only the measured respiratory exchange ratio tells you how much carbohydrate and how much fat is actually being oxidised.

You store the derived performance values in obseed under body data. Recorded sessions are then evaluated against these ranges, making visible how long you spent above the CarbMax range.

Extrapolating a fictitious CarbMax value from a 20-minute test is something we reject. Without gas analysis, substrate use is simply unknown.

Example

In her diagnostic an athlete reaches a carbohydrate use of 90 g/h at 230 W; her CarbMax range sits between 195 W and 230 W. For a 4-hour long-distance bike split she plans 210 W.

Use at 210 W:        approx. 80 g/h
Duration:            4 h
Total requirement:   320 g carbohydrate
Glycogen stores:     500 g (of which approx. 350 g usable)

Without intake the stores would be empty after a good 4 hours, which is not enough with the marathon still to come. At an intake of 70 g/h, 280 g are supplied; net stores drop by only around 40 g, securing the run. The plan rests on measured values, not on an assumption.