Training Numbers That Are Ranges, Not Points

Endurance training runs on single numbers — a VO2 max, a ratio, a watts-per-kilo, a pace. Every one of them is really a range, a ratio with a choice inside it, or a figure that depends on what you counted. These four tools are built to show that rather than hide it.

A VO2 max is a band, not a value

The VO2 Max Estimator runs the Cooper test — how far you cover in 12 minutes — and reports the estimate with its uncertainty attached.

2,400 m in 12 minutes:

Estimated VO2 max	42.4
Realistically no lower than	38.1
— and no higher than	46.6
Width of that range	8.5

The honest result is "somewhere in the low 40s." The range is roughly ±10%, and that is not a flaw in the tool — it is what a field test estimating a laboratory measurement can actually deliver.

Which matters most when you retest. A move from 42.4 to 44 looks like progress and sits well inside the noise. Treat changes smaller than the band as unproven, and compare tests run the same way — same surface, same weather, same pacing discipline — because those move the result more than a few weeks of training does.

The tool also inverts the question: to reach a target of 50 you would need 2,741 m, or 341 m further. That is a far more useful training goal than a number on a scale you cannot directly feel.

The ratio that changes with the method

The Training Load Ratio Calculator compares this week's load against the weeks before it — and shows something usually left out.

Weeks of 370, 380, 400 and this week 450:

Uncoupled — this week vs the 3 before	1.17
Coupled — the conventional calculation	1.13
How much coupling flatters it	0.05

The conventional method includes the current week inside its own baseline, which drags the baseline toward the current week and makes any spike look smaller than it is. The uncoupled version compares this week against the weeks before it — which is the comparison people think they are making.

Coupling always flatters a spike. Here it is 0.05, which sounds small and is exactly the size of gap that moves a number across whatever threshold someone is watching.

⚠️ On thresholds: the tool deliberately does not publish one. The widely-quoted "danger zone" figures have been substantially criticised in the sports science literature, and the arithmetic being sound does not make the cut-offs evidence-based. What the ratio is genuinely good for is noticing — a week that jumps is worth knowing about, whatever number you attach to it.

Watts per kilo depends what you weighed

The Cycling Power to Weight Calculator shows why the same rider quotes two different figures.

250 W, 70 kg rider, 8 kg bike:

W/kg — body weight only	3.57
W/kg — you and the bike	3.21
Share of the total mass that is bike	10.3%

Both are honest; they answer different questions. Body-weight W/kg is the comparable fitness number. Rider-plus-bike is what actually climbs the hill, because gravity does not care which kilograms are which.

And that produces the answer to the perennial question about lighter kit. On a 500 m climb: 22 seconds per kilogram saved. Against a 29-minute climb that is real but modest — and the bike is only 10% of the mass being lifted, which is the context most upgrade decisions are missing.

Your threshold pace is slower than your race pace

The Critical Swim Speed Calculator derives a sustainable pace from two time trials rather than from a percentage of one.

A 400 in 6:20 and a 200 in 3:00:

CSS pace	100 s / 100 m
Your 400 pace	95 s
CSS is slower by	5 s / 100 m

That gap is the point. CSS comes from the difference between the two trials — how much you slow down over the longer one — so it isolates the pace you can hold rather than the pace you can produce for 400 m.

People train at their 400 pace and call it threshold. It is 5 seconds per 100 too fast, which is why those sets fall apart in the back half.

The tool then hands you the actual session paces: CSS + 2s (102) for longer aerobic sets, CSS − 2s (98) for shorter faster ones.

The habit these share

Number	What is hidden inside it
VO2 max 42.4	a ±10% band
ACWR 1.13	a method choice worth 0.05
3.57 W/kg	whether the bike counted
"Threshold pace"	it is 5 s/100 slower than your 400

None of these tools is trying to make you distrust the numbers. They are trying to stop a single figure being read as more precise than it is — which is how people chase noise, mistake a method artefact for a change in fitness, and train at the wrong pace with great discipline.

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General information, not medical or coaching advice. If you have a health condition or are returning from injury, talk to a clinician or a qualified coach before changing your training.