How colours are decided

One run against your usual

A single run is coloured only when it differs from your usual by more than the smallest change worth noticing.

Colours this rule can give: Green, Grey, Red

• Within ±2% for pace and efficiency, ±1.5 points for drift and held, ±2 bpm for heart rate: about your usual (the smallest change worth noticing).
• Beyond it and better: green.
• Beyond it and worse: red.

What is measured

This run against your usual for the same workout type.

Why: one run varies about as much as weeks of real change, so only a change bigger than the smallest one worth noticing is coloured.

Against the plan

On target means as close to the plan as a watch can measure.

Colours this rule can give: Green, Grey, Red

• Within ±2% of the target pace (±3% on reps under 800 m): on target.
• Up to twice that, faster or slower: slightly off, noted.
• Beyond that, faster or slower: clearly off target.
• A planned distance: more than 5% short is clearly off; more than 10% longer is noted in grey, never red (a big step up in distance has its own note).

What is measured

Each target or rep your plan app set, against the pace you ran.

Why: within this band a watch's pace cannot tell you apart from the target.

Easy intensity

An easy run counts as easy when it mostly stays below your first threshold.

Colours this rule can give: Green, Red

• Up to 25% above LT1: stayed easy.
• More than 25% above LT1: harder than easy.

What is measured

Easy and long runs: the share of heart rate above your first threshold (LT1), read before late drift sets in. Not judged for races or long runs with planned faster work.

Why: easy days build the aerobic base only when they stay below the first threshold.

Threshold intensity

Threshold work belongs right at your second threshold, not above it.

Colours this rule can give: Green, Red

• 97–103% of LT2: right at threshold (below it: tempo).
• Above 103% of LT2: over threshold.

What is measured

The work blocks' heart rate against your second threshold (LT2).

Why: threshold work trains best right at the second threshold; well above it, it becomes a harder session than planned.

Interval intensity

Intervals reach their aim when heart rate gets into the VO₂max range.

Colours this rule can give: Green, Grey

• 90% of maximum or more: reached the VO₂max range.
• Below 90%: noted, not a concern.

What is measured

The highest heart rate in the reps against your maximum.

Why: interval training works the heart hardest from about 90% of maximum.

Held (sessions)

Did the session finish as strong as it started? Reps use fixed bands; threshold work is compared with your own usual.

Colours this rule can give: Green, Grey, Red

• 101.5% or more: finished stronger.
• Above 98.5%: even.
• Intervals, 96.5–98.5%: slight fade, noted but not a concern.
• Intervals, under 96.5%: faded late.
• Threshold, below 98.5%: red only when the fade is 1.5 points or more beyond your own usual; without enough earlier sessions, under 96.5%.

What is measured

Intervals: whether the late reps were as fast as the early ones. Threshold: 100 minus the heart-rate drift over the work blocks. 100% = held.

Why: some heart-rate creep at threshold is normal and differs between runners, so a threshold session is compared with your own; rep speed falls with fatigue alike for everyone, so intervals use fixed bands.

Staying power: pace and cost

At the end of a run, two questions: did the pace hold, and did it cost more heartbeats?

Colours this rule can give: Green, Grey, Red

• Pace held: lost less than 1.5%.
• Cost rose: drift above 5% on a continuous run, above 3.5% over work blocks.
• One held and the other not: grey.

What is measured

Did the pace hold, and did each km/h cost more heart rate by the end? The card's colour is always the run's own word above (steady, even, faded…).

Why: one measure, one cut-off: a session's held figure is 100 minus the same drift.

Heart-rate drift

When each heartbeat buys clearly less speed in the second half, the run went beyond today's aerobic endurance.

Colours this rule can give: Green, Red

• Up to 5%: steady.
• −1.5% or lower: stronger late.
• Over 5%: drifted.

What is measured

Easy runs, long runs and races: how much less speed each heartbeat bought in the second half than the first, as measured.

Why: below about 5% a run of this length is within your aerobic endurance; more means it was longer, faster or hotter than your endurance handles today.

Where drift starts (long runs and races)

On long runs and races we show where heart rate starts climbing for good: later and smaller is better.

Colours this rule can give: Green, Grey, Red

• Each run is described, never coloured: the marathon figures behind the rule do not fit a single long run
• Long-run trend: less drift by the end, by at least 1.5 points with its 90% range excluding no change
• Long-run trend: more drift by the end, by at least 1.5 points with its 90% range excluding no change

What is measured

Long runs and races of an hour or more: the point after which heart rate per speed climbs for good.

Why: In 82,303 marathons drift started on average at km 25; runners whose drift started later and stayed smaller ran faster, and adding drift to critical speed cut marathon prediction error by a fifth.

Quarters and blocks within a run

The parts of a run never contradict the whole run's word.

Colours this rule can give: Green, Grey, Red

• Grey when the run reads steady or even.
• Red for the drops only when the run drifted or faded.
• Green for the gains when it finished stronger.

What is measured

Each quarter or block against the first. Small steps can add up across a run, so they never contradict the run's own word.

Why: small steps add up across quarters; coloured on their own they made steady runs look red.

A step up in distance

A run much longer than your longest of the past month is worth a look; weekly load ratios are not.

Colours this rule can give: Grey, Red

• Up to 10% longer, or shorter: nothing is said.
• More than 10% longer: worth a look, with its size: 10–30%, 30–100% or more than 100% longer.
• This week against your last four (acute:chronic) is a number in words only: below 0.8 below usual, up to 1.3 as usual, above it above usual; never coloured.

What is measured

Each run (and each planned session) against your longest run of the 30 days before it.

Why: in 5,205 runners followed for 18 months, a run more than 10% longer than their longest of the previous 30 days came with more overuse injuries (1.5 to 2.3 times the rate); the weekly acute:chronic ratio and week-to-week change did not.

How sure a run's type is

Each run's type carries one word, so you know which types are worth a look.

• Sure: your own answer, the session's name or plan, its recorded steps, a race, or a way of typing that rarely misses.
• Likely: a way of typing that usually matches.
• Unsure: worth a look if the type seems wrong; you can change it on the run's page.

What is measured

The word never decides which runs count: every run feeds your numbers under its type until you change it.

Why: the word comes from how often each way of typing a run matched the type runners gave their own runs.

Trends over weeks

A trend turns green or red only when it is unlikely to be chance.

Colours this rule can give: Green, Grey, Red

• Improving: 90% sure it moved the good way.
• Unclear: too little evidence either way.
• Declining: as sure it moved the other way.

What is measured

Progress and Today judge a trend only when its whole range moves past the smallest worthwhile change.

Why: a trend is coloured only when it is unlikely to be chance.

Heat and other conditions

Heat, hills and other conditions explain a run; they never rewrite its colour.

Colours this rule can give: Grey

• Shown beside the measured figure ("about 2 pts of it from the heat"): it never changes a run's word or colour.
• It can explain a fade, never turn it into a stronger finish.
• Trends over weeks are judged as measured; when warm weeks move them, the share from the heat is stated beside the verdict.
• Acclimatisation: once your runs confirm it, heat costs less after recent warm running; it never turns heat into a benefit (Périard et al. 2015; Daanen et al. 2018).
• A condition counts only when your own runs confirm it, in the direction physiology expects. What affects you and the run pages use this same rule.

What is measured

How much a condition cost a run, learned from your own runs: heat (temperature with humidity), hills, wind, time of day, resting heart rate and HRV.

Why: a run is judged as it happened; conditions explain it, they do not rewrite it.

Morning read of a session

Before a session: the heart rate your own runs predict at its pace, and how often that prediction has held.

Colours this rule can give: Green, Grey, Red

• Inside the range: as expected
• Under it: easier than usual for the pace
• Over it: harder than usual for the pace
• The range is built to hold about 90% of the time from your own past errors; the card shows how often it really held.

What is measured

Before a planned session, the heart-rate range your own recent runs of that type predict at its pace, as measured; the day's heat is stated beside it once your runs confirm heat, never added. After the run, its heart rate is checked against the range for the pace it actually ran.

Why: the range is a reading guide, not a target: a session outside it is information, and the honest hit count shows how far to trust it.

Overnight notice

We speak up only when your nights are off two mornings running, with no hard session to explain it.

Colours this rule can give: Grey, Red

• Said only when 2+ of them are outside your range on 2 mornings in a row, with no hard session or race in the 2 days before.
• It describes how to read the next run; it never tells you to rest or skip.

What is measured

Each morning's HRV, resting heart rate and sleep against your own usual nights.

Why: one rough night is common and means little; two in a row with nothing to explain them is worth knowing.

Recovery after a hard session

After a hard session: whether your mornings are back to your usual, against your own past recoveries.

Colours this rule can give: Grey, Red

• Not back yet, within your usual nights: normal
• Not back past your usual nights: worth a look

What is measured

After a threshold, interval or long session or a race, each morning's resting HR (or HRV, when your watch records it) against your usual mornings. Shown only while you are not back yet, once your past sessions of the kind say what is usual for you.

Why: recovery is personal; your own usual tells more than a fixed number of hours, and a normal recovery needs no note.

Back after a break

After a break, your first runs back are compared with your runs before it.

Colours this rule can give: Green, Grey, Red

• Better than before the break
• Within your usual range from before
• Below before the break: expected after time off

What is measured

14 days or more without a run is a break. For your first weeks back, Today shows each type's latest run against your runs of that type before the break, with the run page's "against the usual" rule. It never changes a trend or a verdict.

Why: aerobic fitness falls measurably after two to four weeks without training and a shorter gap barely moves it, so a fixed two weeks applies to every runner.

What limits your marathon

Your marathon's share of critical speed against runners of your time says whether staying power or the engine is where the time is.

Colours this rule can give: Red, Grey, Green

• 2 points or more below the share runners of your finish time hold: staying power is where the time is (worth a look); the card says how many minutes it is worth.
• Within 2 points either side: close to the usual, neither part is called the limit.
• 2 points or more above it: staying power is kept, and the engine (critical speed) is where the time is.
• Speed at VO2max: context only, never ranked.

What is measured

Your marathon pace as a share of your critical speed (staying power), against what runners of your finish time hold.

Why: marathon speed is critical speed times the share of it held for 42 km (Joyner & Coyle 2008); faster finishers hold a larger share, so the share is read against runners of the same time, not one fixed number.

Carbohydrate during a race

A race's carbohydrate per hour is read against the 60–90 g the evidence supports.

Colours this rule can give: Green, Red, Grey

• 60–90 g an hour: in range, keep.
• Below 60 g an hour, none taken included: worth a look.
• Not recorded, or above 90 g an hour: said, not judged.

What is measured

The carbohydrate you noted for a race (its Fuel card), per hour of its result.

Why: in races of 2.5 hours or more, 60–90 g of carbohydrate an hour holds pace late; up to 90 g with glucose–fructose, after gut training.

Aerobic efficiency

Can I run faster without a higher heart rate?

How much running speed you get for your heart rate. On similar easy or long runs, more speed at the same heart rate can be a useful sign of progress.

How to read it

Higher can be encouraging on similar runs. First check the pace and heart-rate readings: a sensor reporting too few beats can also make this number look better.

Limits

This does not measure oxygen use in a lab. Hills, heat, wind, fatigue, hydration and watch heart-rate errors can change the ratio. An unusually low heart rate can be a bad reading, not better fitness. Compare similar efforts.

Sources

• Workload decoupling and marathon durability
• Running economy: measurement and determinants

Heart-rate drift

Am I working harder to hold my pace near the end?

How much harder your heart has to work for your speed later in a run. It is most useful on a fairly steady easy or long run.

How to read it

A positive number means speed cost more heart-rate effort later. Near zero means little change. A negative number means the opposite, but can reflect warming up or running downhill. A change from 5% to 3% is a drop of 2 percentage points.

Limits

Hills, a planned faster finish or warming up can explain the result. There is no single cutoff that proves you are ready for a race. The linked study uses a different calculation; it explains the background, not the accuracy of this app’s formula.

Sources

• Workload decoupling and marathon durability

Drift by the end

Is my heart rate holding better late in my long runs?

How much more heart rate each km/h cost at the end of your long runs than at their start, and whether that is shrinking over time.

How to read it

Lower is better. The trend uses the same rule as every trend in the app: a change of at least 1.5 points whose 90% range excludes no change. In 82,303 marathons drift started on average at km 25 and was about 16% by km 35–40; runners with less drift ran faster (Smyth et al. 2022). Those are marathon figures, so a single long run is described, not coloured.

Limits

Heat, humidity, fuelling and the pace you choose all change it, and heat is not taken out of a single run. Compare long runs of a similar length: a 30 km run has more room to drift than a 16 km one.

Sources

• Workload decoupling and marathon durability

Threshold pace evidence

Am I completing comparable sustained quality work at a faster pace?

The pace you ran in the harder, sustained part of a threshold or tempo workout. It helps compare similar sessions; it does not measure your lactate threshold, and only threshold runs feed the LT2 estimate.

How to read it

A lower time per distance means faster running. Every session plots one qualifying run; Weekly average takes the arithmetic mean of that family’s available observations. A faster workout is not automatically a shifted lactate threshold.

Limits

The heart-rate fallback, used only without work blocks, mixes more of the run. Hills, heat, workout design and HR lag change the observation. Interval repetitions have a separate work-pace metric and do not become LT2 evidence just because they are fast.

Sources

• LT1 and LT2: measurement methods
• Monitoring athlete training loads: consensus statement

Work-section efficiency

In my threshold work, do I produce more speed for the same heart rate?

How much speed you produce per heartbeat in the hard part of threshold and tempo runs, without the warm-up, floats and recoveries.

How to read it

Higher can mean better aerobic efficiency at threshold intensity, but only across comparable sessions: heat, hills and how hard the session was run all move it. It is descriptive: shown, not judged improving or declining.

Limits

Wrist heart rate often lags or spikes at the start of hard blocks. This is a field ratio, not laboratory running economy.

Sources

• Workload decoupling and marathon durability
• Running economy: measurement and determinants

Durability

Am I finishing as steadily as I started?

How well you hold your running efficiency toward the end. A value near 100% means the late part was much like the early part.

How to read it

100% means you held the same efficiency. Below 100% means it fell; above 100% means it rose. Hills and warming up can change the result too; sessions planned to get faster are left out or compared only within their same-length blocks.

Limits

This is not a direct measure of tired muscles or proof of race readiness. Holding speed during intervals is different from holding speed relative to heart rate on a long run; do not treat those percentages as the same measurement.

Sources

• Workload decoupling and marathon durability

Interval work pace

Are my work repetitions getting faster under a comparable interval protocol?

Your average pace during the fast repetitions only. Rest, warm-up and cool-down are left out. The trend compares sessions with reps of a similar length.

How to read it

Lower min/km or min/mi is faster. Compare like-for-like rep length, count and recovery; faster short reps cannot be read as improvement over slower long reps without that context.

Limits

Rep detection and pace quality matter. It does not measure VO₂max, anaerobic capacity or LT2, and a faster average may simply reflect easier recoveries or shorter work.

Sources

• Monitoring athlete training loads: consensus statement

Work-rep speed retention

Do I hold my rep speed to the end of an interval session?

Whether your later reps were as fast as your early ones, in interval sessions with reps of the same length.

How to read it

100% means you held your speed; below 100% means you faded; above means you finished faster. It is descriptive: shown, not judged, because pacing plans (negative splits) change it on purpose.

Limits

Speed only, not heart rate: it does not say what holding the speed cost. GPS on short reps and track bends can move it by a few percent.

Sources

• Workload decoupling and marathon durability

Measured LT1

What first-threshold reference did my laboratory assessment identify?

Your lab’s first effort boundary: a guide to where comfortable running starts becoming more demanding.

How to read it

Read the test date, protocol and threshold-identification method. This measured reference is separate from the selected-period field estimate.

Limits

Threshold methods and protocols differ. A historical laboratory result does not automatically represent current fitness, and a selected stage is not an exact all-conditions boundary.

Sources

• LT1 and LT2: measurement methods

Measured LT2

What sustained-intensity reference did my laboratory assessment identify?

Your lab’s second effort boundary: a reference for sustained, demanding running. It is not a pace you can hold indefinitely.

How to read it

Compare assessments with similar protocols and methods. LT2 is not a guarantee that one exact pace can be held for one fixed duration.

Limits

Test age, protocol, stage length and threshold method affect transfer to outdoor running. Laboratory and field estimates must remain distinguishable.

Sources

• LT1 and LT2: measurement methods

Critical speed

What does my fastest running suggest about my sustained speed?

The fastest pace you can sustain for a long time, estimated from your fastest efforts in recent training (Smyth & Muniz-Pumares 2020). It describes your performance pattern, not a speed you can hold forever.

How to read it

Higher modelled speed can support improved performance if the effort range, conditions and maximal effort are comparable. Sparse or poorly matched efforts make the fit unreliable.

Limits

The app does not prove efforts were maximal or standardize courses. It is not a lab test or an individualized prescription.

Sources

• Smyth & Muniz-Pumares 2020, critical speed from training data

Fuel

Estimate without a lab test, from your pace, the gradient, your weight and your LT1/LT2

How to read it

A likely range, not a lab measurement: runners differ in economy and in how much fat they burn at the same effort. Time above LT2 is counted as mostly glycolytic, never as a fat figure. Food before and during the run, heat and your diet move it; it describes the run and is never a verdict, and the card never shows how much glycogen is left. A lab test with gas exchange can check it.

Sources

• Léger & Mercier 1984; ACSM; Minetti et al. 2002
• Romijn et al. 1993; Jeukendrup & Wallis 2005
• Intake guidance: Jeukendrup 2014; Thomas, Erdman & Burke 2016