Which calculator for which situation
- Running. Pace converts between pace, distance and time; race prediction estimates a time at one distance from a result at another; steps per mile calibrates your tracker to your height.
- Intensity. Heart rate and training zones define the bands; VO₂ max estimates aerobic capacity.
- Strength. One-rep max estimates maximum load from a submaximal set; training load organises weekly progression.
- Composition. FFMI relates lean mass to height — the index that does for muscle what BMI was supposed to do for weight.
- Swimming. Swim pace, with pool distances and splits.
Three things the literature shows and intuition resists
1. Most training should be easy. The most consistent finding in endurance research is that around 80% of volume belongs at low intensity, with only 20% at high intensity. The trap is the middle zone — too hard to recover well, too easy to drive high-intensity adaptation. It accumulates fatigue without delivering the benefit of either end.
2. Max heart rate formulas are badly imprecise. Both 220 − age and Tanaka's (208 − 0.7 × age) carry a standard deviation of 10 to 12 beats between people of the same age. Two 40-year-olds can have true maxima of 165 and 195, and the formula tells both of them 180. Use it as a starting point and adjust by perceived effort.
3. The "fat-burning zone" exists and does not do what it seems. At low intensity the proportion of fat in the fuel mix is higher — that part is true. But total expenditure is far lower, and what determines fat loss is the day's deficit, not the hour's fuel mix.
One-rep max: estimating instead of testing
Testing a true one-rep max requires a long warm-up, solid technique and ideally a spotter. So it is estimated from a submaximal set, using formulas such as Epley's and Brzycki's.
Accuracy falls as the repetition count rises: up to 5 reps the estimate is good; above 10 it becomes a rough approximation, because it starts depending heavily on individual muscular endurance rather than maximal strength alone.
Frequently asked questions
How do I find my real max heart rate? Only by testing, never by formula. The gold standard is a supervised graded exercise test. Maximal field tests exist but require a training base and are not appropriate for beginners or anyone with cardiovascular risk factors.
Why does my pace worsen in heat at the same effort? Because part of the blood flow is diverted to the skin to dissipate heat, and heart rate rises for the same work — cardiac drift. Training strictly by heart rate on a hot day makes you run slower than you could.
Does FFMI measure the "natural limit"? The value of 25 comes from a 1995 study with a small sample. It is a useful statistical reference, not a verdict about any individual.
Should I train by pace or by heart rate? Pace controls the outcome; heart rate controls the effort. On a hot day, after poor sleep, or uphill, pace lies about the cost — there heart rate is the better guide.