What INSCYD Testing Actually Measures (And Why I Use It)

Why I Use INSCYD Testing

Most athletes train off a percentage. Your zones get set as a fraction of FTP or heart rate max, and every session gets labeled accordingly. That works fine as a starting point, but it treats every athlete's physiology as if it were the same shape, just scaled up or down. It isn't.

INSCYD testing is the tool I use to get past that assumption. Instead of estimating your training zones from a single number, it builds a full metabolic profile: how much oxygen you can use, how quickly your glycolytic system produces lactate, where your thresholds actually sit, and how your body splits fuel between fat and carbohydrate at every intensity. That profile is what the rest of your training plan gets built around.

The Four Numbers That Actually Matter

An INSCYD test produces four core metrics. Each one on its own tells you something. Together, they tell you where your training should actually focus.

VO2max

VO2max is your maximal oxygen uptake, the ceiling on how much oxygen your heart, lungs, and muscles can deliver and use during hard effort. It has been the standard measure of aerobic fitness in exercise physiology for decades [1]. It sets the upper bound on your aerobic engine, but it doesn't tell you how efficiently you use that engine, which is where the other three numbers come in.

VLaMax

VLaMax is your maximal lactate production rate, a measure of how aggressively your glycolytic system engages as intensity rises. Cyclists with a high VLaMax burn through carbohydrate and produce lactate quickly, which suits short, explosive efforts. A lower VLaMax favors sustained, steady output. Most athletes have never measured this number, and that's a problem, because it's often the reason two riders with the same FTP have completely different strengths.

Lactate Thresholds (LT1 and LT2)

LT1 and LT2 mark the boundaries between your aerobic, mixed, and anaerobic training zones. Determining them accurately, rather than estimating them from a percentage of FTP or max heart rate, is one of the more contested areas in exercise science, and the methodology matters [2]. INSCYD calculates both from your metabolic profile rather than a single field test, which removes a lot of the guesswork in setting your zones.

Fat Oxidation (FatMax)

FatMax is the intensity at which your rate of fat oxidation peaks. It was first defined by Achten, Gleeson, and Jeukendrup [3], and it varies significantly between individuals, even among athletes with similar FTPs. Knowing your FatMax tells me how to structure your base training and your race-day fueling strategy, instead of guessing at both.

What This Changes About Your Training

Once I have these four numbers, I stop prescribing training zones as percentages and start prescribing them against your actual physiology. If your VLaMax is high and it's suppressing your threshold power, the fix looks different than if your limiter is VO2max. If your fat oxidation is poor, your fueling strategy for long rides changes. None of that shows up in a standard FTP test.

The same data lets me pace you more precisely for races and long events, because I know roughly how much carbohydrate you're burning at a given wattage and where your thresholds actually sit, not where a formula assumes they sit. Retesting every few months tells us whether training is actually moving the numbers we're trying to move, rather than assuming a block worked because it felt hard.

Who Should Get Tested

I use INSCYD with road racers, gran fondo riders, and anyone training seriously enough that guessing at their zones is costing them fitness. If you've plateaued despite consistent training, or you've never actually measured your metabolic profile and are training off assumptions, this is the test that tells you what's actually going on.

Booking a Test

If you want to see where your numbers actually sit, get in touch and we'll get you scheduled.

Schedule a Test

References

[1] Bassett, D. R., & Howley, E. T. (2000). Limiting factors for maximum oxygen uptake and determinants of endurance performance. Medicine & Science in Sports & Exercise, 32(1), 70-84.

[2] Faude, O., Kindermann, W., & Meyer, T. (2009). Lactate threshold concepts: how valid are they? Sports Medicine, 39(6), 469-490.

[3] Achten, J., Gleeson, M., & Jeukendrup, A. E. (2002). Determination of the exercise intensity that elicits maximal fat oxidation. Medicine & Science in Sports & Exercise, 34(1), 92-97.