The calculators give you a number. These explain where the number comes from, which model it uses, and how much to trust it — including the places where the sports science genuinely disagrees with itself.
Converting an activity file is a lossy operation in one direction and impossible in the other. What each of the three formats actually stores, which conversions are safe, and why the same run shows different elevation on different platforms.
The 220-minus-age formula has a standard deviation of about 10-12 beats per minute. Here is where it came from, why it misses, and what to use instead — including how to find your real maximum and threshold.
Going out too fast costs more than the time you gained. What the pacing evidence actually supports, why even pace and even effort are different targets, and how to build a plan you can hold when adrenaline says otherwise.
Every race predictor extrapolates one performance to another distance. The models differ, they all assume something you may not have done, and the marathon is where they most often lie to you.
Training load models compress a week of sessions into one number. Here is what each model is built from, what it cannot see, and why the acute:chronic workload ratio is far more contested than its popularity suggests.
Three calculators, three answers, hundreds of calories apart. The disagreement comes from two places — which BMR equation is used and how activity is multiplied — and neither is a rounding error.
Every tool on raacon/ runs in your browser — see about for how that works.
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