Concepts
Training load
How Runtool measures training load — session load, acute and chronic load, ACWR, and fitness, fatigue, and form.
Training load is Runtool's answer to "how much training is this, really?" — a single scale that makes a hill session, a long run, and a bike ride comparable, and that shows whether your training is building up at a rate your body can absorb.
Session load
Every completed workout gets a session load built from three components:
- Aerobic — the steady cardiovascular work.
- Metabolic — the cost of time spent at and above threshold.
- Neuromuscular — the strain of fast running and hard efforts.
The split is why a 45-minute interval workout can out-load a 90-minute easy run: they stress different systems, and the load says so. With pace and heart rate timeseries the number is precise; without them, Runtool estimates from what it has.
Load for a workout you logged by hand
A workout you typed in has no heart rate trace, so the load is estimated. Runtool uses the best input you gave it:
| What you entered | How the load is worked out |
|---|---|
| Distance and time, and you have pace zones | The pace of each part of the run, converted to effort |
| An RPE and a duration | The effort your RPE describes, over that time |
| A duration only | The typical effort of that workout category, over that time |
Every estimate is labelled. Hover the Load value on the workout page or the calendar and it says which of the three produced the number — "From your zones", "From RPE", or "From duration" — so an estimate is never mistaken for a measurement.
The three land on the same scale, so a logged run and a synced one are comparable, and connecting a device later will not make your load jump.
Two things improve an estimate, in this order:
- Set your pace zones. With zones, the distance and time you entered price the run directly. This is the largest single improvement.
- Add an RPE. Without zones, the effort rating is what separates a hard hour from an easy one.
Projected load
A workout you have not done yet carries a projected load — the same number, on the same scale, worked out from the workout's structure and your zones. It is what lets you see the load of a week before you run it, and it feeds the forward part of your ACWR.
Projected load is a forecast, so it is replaced by the real number once you complete the workout. It is deliberately conservative: where Runtool has less to go on, it estimates low rather than guessing high.
What it is based on depends on the workout:
| Workout | Projected from |
|---|---|
| Run, with your pace and heart zones | Its structure — every rep, recovery, and interval |
| Run, with pace zones only | Time spent in each pace zone |
| Strength or cross-training | Planned duration |
| Race with a goal time | The goal time over the race distance |
| Race without a goal time | The finish time your current threshold predicts |
Some workouts show no projected load, and the workout tells you why when you hover it:
- Runs, when you have no pace zones set. A run's load comes from your zones. Without them Runtool would be guessing, so it shows nothing rather than a number you can't trust. Set your zones and it fills in.
- Workouts created from an imported activity. These already happened, so they carry their real load — there is nothing to forecast.
Acute and chronic load
Session loads roll up into two running values:
- Acute load — what you've done recently, weighted toward the last days. Your current stress.
- Chronic load — your baseline, built over weeks of training. What you're adapted to.
Fitness grows by nudging acute load above chronic load, repeatedly, with recovery in between. Both curves live in the load widget on the Overview.
ACWR
The acute:chronic workload ratio (ACWR) divides one by the other. Around 1.0, training matches what you're adapted to. Push well above it and injury risk climbs — the classic training-ramp signal.
Runtool colors only the bands that need attention — caution and risk — and leaves everything else neutral. No alarm theatre: if your chart is quiet, your ramp is fine.
Fitness, fatigue, and form
The fitness lens (beta) reads the same load history three ways:
- Fitness — the slow-moving product of chronic training.
- Fatigue — the fast-moving cost of recent work.
- Form — fitness minus fatigue: your readiness to perform right now.
Fatigue rises faster than fitness but fades faster too — that's why a taper works, and you can watch it work on the chart: fitness holds while fatigue drains away into positive form on race day.
Choosing a load method
The Training load method preference controls how heart rate data converts into load: EPOC-based, exponential (weights high intensity more aggressively), or a 50-50 blend. See Athlete settings. Whichever you choose, it applies consistently, so trends stay comparable.