Method

Your file tells me what happened.

You tell me how it felt. I read the raw file of every key session: power, heart rate, terrain, cadence. Not the app summary. This is what comes back to you.

Fuel

Burned against eaten, hour by hour.

From your power I estimate how much carbohydrate each hour cost you. Against it goes what you actually ate. The gap comes out of your stores, and when the stores run low, the fade starts. Many late-race collapses are a fuel problem that looks like a fitness problem.

Then we practise the race-day number in training, so your gut is ready on the day.

Illustrative bar chart of a 4-hour ride. Each hour the rider burns 130 to 150 grams of carbohydrate but eats only 45 to 60 grams. The gap comes out of glycogen and reaches about 330 grams by hour 4, which is when the late fade sets in. — **Fig. 1**Illustrative rider, 4-hour ride. Burn estimated from power; intake follows published guidance (Wallis and Podlogar 2022).

Engine and battery

One number is never the whole story.

Your engine is the power you can hold for a long time. Your battery is the extra work you can spend above it before you have to back off. Two riders with the same engine can race very differently: the bigger battery wins the short climbs and the attacks, the engine settles the long efforts.

I estimate both from your own files, give each a range, and say which test would firm it up.

Illustrative power-duration curves for two riders with the same critical power of 300 watts. The rider with a 24-kilojoule battery holds 433 watts for 3 minutes against 367 watts for the rider with 12 kilojoules. At 20 minutes the gap shrinks to 10 watts. — **Fig. 2**Two illustrative riders, not real athletes. Engine = critical power (W). Battery = work capacity above it (kJ).

System

Everything that moves your power, and what it buys.

Training, fuel, sleep and heat shape your physiology. Your physiology sets your power. Then aero, position, weight, equipment, course and pacing decide how much speed each watt buys. We work on the parts that move yours, not on all of them at once.

Diagram. What you do (training, fuel, recovery and sleep, heat and hydration) shapes your physiology (VO2max, utilisation, efficiency, durability, strength). Physiology sets your power. Power buys speed, and aero, position, body mass, equipment, course and wind, and pacing decide how much speed each watt buys. — **Fig. 3**Simplified. Dashed boxes are logged or inferred, not measured directly.

Rules I keep

Terrain first. A slower second hour is not tiredness if the road climbed.
Same window, same effort. I only pair heart rate and power that happened together.
Race day is not training day. Adrenaline lifts early race heart rate, so your zones never come from a race file.
Every number labelled. Lab, field or estimate. If it is an estimate, you get the range.

You see the outputs. The models behind them stay mine.