Load: effort with no ceiling.

Why no ceiling

Capped scales, such as a strain score from 0 to 21, get harder to move the higher you go, so a long day and a very long day can end up looking the same. Load stays linear. An hour in Zone 2 is about 120, and three hours is about 360. A 54-minute threshold run is about 175.

Resting doesn’t count: sleep scores 0, and everyday walking rarely registers.

How a minute is counted

Each minute scores by how far your heart rate sits between resting and maximum, its share of your heart-rate reserve:

HRR    = (HR − resting HR) ÷ (max HR − resting HR)
points = 10 × (HRR − 0.45) a minute, from 0 to 5.5

The middle of each zone scores its zone number: Zone 1 about 1 point a minute, Zone 2 about 2, up to Zone 5 at about 5. This is Edwards’ zone-weighted TRIMP, made smooth so there are no cliffs at the zone boundaries. Below 45 % of your reserve, a minute scores nothing. Each minute is read as the median of its samples, the same minute Keely uses to find the workout and draw its chart, so one noisy second over a zone’s floor never moves a minute into the next zone.

Heart rate comes from the Loop’s 24/7 recording, a sample every 5 minutes at rest and every second during activity, and from live streaming when Keely is open during a workout.

Heart-rate zones

• Z1 Recovery 50–60 %
• Z2 Endurance 60–70 %
• Z3 Tempo 70–80 %
• Z4 Threshold 80–90 %
• Z5 VO₂ max 90–100 %

Zones are shares of your heart-rate reserve (the Karvonen method), between two anchors:

• Resting heart rate: the average of your last 7 nightly resting heart rates.
• Maximum heart rate: the most your heart held for 30 seconds in a workout (the window’s 20th percentile), among the measured workouts of the last 90 days that weren’t in water and weren’t multisport events. A hold counts on its own only within 15 bpm of Tanaka’s estimate, 208 − 0.7 × age; above that, another workout’s hold within 5 bpm must back it up, so one optical spike never sets your zones for three months. Before your first workout, it uses the estimate. A workout’s page still shows its 5-second peak. Your own setting always wins.

The app shows where each anchor came from and when, for example “Max 188, observed 14 Sep, hill repeats”.

Today’s target

Each morning Keely sets a range for the day from your usual Load and how recovered you are:

chronic = your average daily Load over the last 28 days
centre  = chronic × (0.2 + 0.014 × Recovery)
target  = centre ± 15 %

At 81 % Recovery the centre is 1.33 times your usual day; at 54 %, 0.96 times; at 23 %, 0.52 times. Until you have 14 days of history, Keely starts from a typical day, a chronic Load of 110, and targets begin after your first Recovery.

Through the day Today tells you where you stand: room for more, in target, or over. Going over on a Restore day comes with a nudge to sleep early.

Balance

Balance compares your last week with the three weeks before it: the average daily Load of the last 7 days divided by the average of the 21 days before them. A day counts when your Loop was worn for 10 hours or recorded a workout, so a day without the band is left out, never counted as rest. It appears with 4 such days in the week and 14 in the three weeks before, and says "not enough recent training to compare" when your usual day is under 15.

The card shows both loads ("this week 145 a day · your usual 110") and how many days were measured. It describes the change; it doesn’t predict injury. The cut-offs once used for that came from team sports and predict injury barely better than chance.

Workouts

Keely finds workouts in your heart rate, with nothing to start or stop: at least 10 minutes at or above the Zone 1 floor, with dips of up to 2 minutes allowed. It also reads the sports inside a workout from each minute’s regime (running cadence, a still wrist, walking cadence, or the wrist in water), and joins adjacent workouts of different sports with the heart still up between them into one event with legs: a triathlon, a duathlon, an aquathlon or a brick session, each leg with its own Load and heart rate, offered as a suggestion you confirm. Each workout is classed by where its minutes went:

Each workout also shows its Load, time in each zone, a recovery time (10 + 0.12 × Load × (1.35 − Recovery ÷ 100) hours) and, when the Loop recorded every second, your 1-minute heart-rate recovery: how far your heart rate fell in the minute after your last hard effort.

You can name a workout, change its start and end, or add one Keely didn’t see, and it’s measured again from your heart rate. Keely learns from what you do: workouts like ones you’ve named are suggested with the same name, and named for you once four agree, and easy blips you keep removing stop being found. When your wrist is in the water, the Loop’s skin temperature tells Keely it’s a swim, and the swim starts when you got in. A walk or run that a watch or app saved to Apple Health with its distance also shows its pace, and feeds your Fitness.

Frequently asked questions

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