Every ride in WattPlan gets a Load, a single figure for how much training stress it carried. With a power meter that calculation is straightforward, and without one there is still an answer that is better than most riders assume.
Power first, heart rate second
When a ride arrives, WattPlan prefers power, because power is a direct measurement of work done, it responds instantly, and it does not care whether you slept badly or drank coffee.
When there is no usable power in the file, it works the Load out from heart rate instead, using a method published by Banister known as TRIMP, for training impulse. The principle is that time spent at a higher fraction of your heart-rate range counts for disproportionately more than time spent low, which matches how training stress actually accumulates.
The ride is then scored on the same scale as a power-based ride, so your chart does not develop a step every time you ride without a meter.
The three numbers it needs from you
The heart-rate calculation cannot run on heart rate alone, because it needs to know where your heart rate sits within your own range. That means three figures in your profile.
- Maximum heart rate
- Resting heart rate
- Lactate threshold heart rate, the rate you can hold for roughly an hour of hard effort
Without those the estimate falls back to something cruder, and with them it is genuinely useful. It takes about ten minutes to set up and most riders never do it.
The weighting also differs slightly between men and women, following the original research, and WattPlan applies the appropriate coefficient from your profile.
What it checks before trusting a file
Heart-rate straps produce nonsense more often than power meters do, so the calculation filters before it counts.
Samples below about 30 beats a minute, or above your maximum by more than a few per cent, are discarded as artefacts from dropouts, interference or a strap losing contact. If fewer than eighty per cent of the samples in a ride survive that filter, the file is treated as unreliable and no heart-rate Load is produced, rather than a confident wrong number being written into your chart.
So an occasional ride showing no Load usually means the strap was misbehaving, not that the ride did not count.
Where it is weaker than power
Short, sharp efforts are under-counted. Heart rate lags effort by thirty seconds or more, so a thirty-second sprint is largely over before your heart rate responds, and a session of short intervals will score lower than it deserves.
Heat, dehydration, stress, caffeine and illness all move heart rate without changing the work done, so a ride in August can score higher than the same ride in March.
Cardiac drift inflates long rides. Heart rate climbs through a long steady effort at constant power, which nudges the figure upward.
Steady endurance riding is where heart rate is at its most reliable, and it is also the majority of most riders' winter.
Using it well
Set the three heart-rate numbers properly and update your maximum and threshold once a year rather than never. Wear the strap consistently, because a chart with gaps in it is harder to read than one with slightly imperfect figures, and wet the contacts before you start, which removes most dropouts.
Then treat it as a trend rather than a precise score. It does not matter whether a particular ride came out at 68 or 74, only whether your Fitness line is climbing across a month, and heart-rate Load answers that question perfectly well.
If you later add a power meter, nothing breaks. WattPlan starts preferring power on the rides that have it, and your history stays intact.