What Is Training Load in Running? Explained Simply

Two runners each run 40 km in a week. One jogs every kilometre; the other does intervals, a tempo run and a hard long run. Same distance, very different stress on the body. Training load is the number that captures that difference.

What training load means

Training load is a score for how much stress a run puts on your body, based on how long it lasted and how hard it was. Longer runs add more load. Harder runs add a lot more. Add up all your runs for a week and you get your weekly training load.

Once you know your load, you can answer the two questions every runner has: am I doing enough to improve, and am I doing so much that I will get hurt?

How training load is measured

Heart-rate load (TRIMP)

The most common method is TRIMP (training impulse), first described by sports scientist Eric Banister. Each minute counts more the higher your heart-rate zone. Windlace uses these weights per minute:

Heart-rate zone	Load per minute
Zone 1 Recovery	1.2
Zone 2 Aerobic base	1.9
Zone 3 Tempo	2.7
Zone 4 Threshold	3.6
Zone 5 and above	4.6

Worked examples

Easy 60 minutes, all in Zone 2: 60 × 1.9 = 114.
45-minute tempo run: 30 minutes in Zone 2 (30 × 1.9 = 57) plus 15 minutes in Zone 4 (15 × 3.6 = 54) = 111. Shorter, but almost the same load as the hour.
Recovery jog, 30 minutes in Zone 1: 30 × 1.2 = 36.

No heart rate? Use effort (session RPE)

Rate the whole run from 1 (very easy) to 10 (all out), then multiply by minutes. A 45-minute run at 7 out of 10 gives 315; a 60-minute easy run at 3 gives 180. The numbers are on a different scale, but the idea is the same.

Session load = minutes × effort (1 to 10) Simple, free and surprisingly good. Use the same method every time so the weeks can be compared.

Acute vs chronic load: the key idea

Your body gets used to the load you normally do. Trouble comes from sudden jumps, not from high load in itself. That is why coaches compare two numbers:

Acute loadWhat you did this week. Shows how tired you are right now.

Chronic loadYour usual week: the average of the last 4 weeks. Shows what your body is used to.

Divide acute by chronic and you get the acute to chronic ratio. Research on athletes, notably by Tim Gabbett, found that injury risk tends to rise when this ratio climbs well above about 1.5.

The ranges Windlace uses. Example: a usual week of 400.
This week vs usual	Status	Example load	What it means
Below 0.8×	Low	under 320	Less than usual. Fine for rest weeks.
0.8× to 1.3×	Optimal	320 to 520	Good for getting fitter.
1.3× to 1.5×	High	520 to 600	More than usual. Plan easy days.
Above 1.5×	Overtraining risk	over 600	Much more than usual. Injury risk goes up.

How to build up safely

Know your usual week. Look at the average load (or kilometres) of your last 4 weeks.
Stay in the optimal range most weeks: about 0.8 to 1.3 times your usual week.
Raise it step by step. As your usual week grows, so does your optimal range. Small steps every week add up.
Add a lighter week every 3 to 4 weeks. Drop to about 70 to 80% so your body can absorb the work.
Come back slowly after a break. After illness or a holiday your usual week is lower, so the same old week is now a big jump.

Common mistakeAdding speed work and extra kilometres in the same week. Hard running raises load much faster than easy running, so add one thing at a time.

Signs your load is too high

Heavy legs that do not clearEasy runs feel hard for several days in a row.

Higher resting heart rate5+ bpm above normal in the morning, often with lower HRV.

Poor sleep and low moodRestless nights, irritability, no motivation to run.

NigglesSmall aches that keep coming back. A warning before a real injury.

How to track your training load in Windlace

Add your runs. Windlace works out each run's load from its second-by-second heart rate. Runs without heart rate count each minute as Zone 2.
Open the Fitness tab. See this week's load (it resets every Monday) against your optimal range from your usual 4 weeks.
Check the last 8 weeks. Each bar is coloured Low, Optimal, High or Overtraining risk, against that week's own range.
See each run's load. Every run shows its load, coloured against an average run day in your optimal week.

Windlace training load with the optimal range

Weekly training load with your optimal range (left) and the Fitness tab (right).

Key takeaways

Training load scores how much stress a run puts on your body, from its length and how hard it was.
Heart-rate load (TRIMP) weights each minute by zone; without heart rate, use minutes × effort.
Compare this week (acute) with your usual 4 weeks (chronic): sudden jumps cause most problems.
Optimal is about 0.8 to 1.3 times your usual week; above 1.5 times, injury risk rises.
Build step by step and take a lighter week every 3 to 4 weeks.

Frequently asked questions

What is a good training load?

There is no single good number. A good load is one inside your own optimal range, about 0.8 to 1.3 times your usual week, rising slowly over time.

Is training load the same as mileage?

No. Mileage counts distance only. Training load also counts how hard you ran, so 10 km of intervals adds much more than 10 km of easy jogging.

What is the acute to chronic workload ratio?

It is this week's load divided by your average week over the last 4 weeks. Around 0.8 to 1.3 is a good range; well above 1.5 is a big jump that raises injury risk.

How do I lower my training load?

Run fewer hard sessions, shorten your runs, or replace a run with rest or easy cross-training for a few days.

Does training load count strength training?

Running apps usually only count runs. If you lift or cycle a lot, keep that in mind when your running load looks low.

See your training loadAdd your runs and Windlace shows your weekly load against your own optimal range.

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Windlace Editorial TeamGuides on training, fitness and racing from the team behind Windlace, Your AI Running App. We write in plain words and check our facts against published research.

What is training load, and how much is too much?