Frequently Asked Questions

Does Fuse work with Strava?

No. Strava's API policy prohibits using Strava data with AI applications, and Fuse's coaching is AI-based — so we can't support a Strava connection, either directly or through a third-party sync service.

If you connected Strava during our alpha, the activities already in your history stay there and remain visible to you. No new Strava data will sync.

The good news: most of what Strava records reaches Fuse anyway if your watch is connected. Garmin, Apple Health, Samsung Health and Polar all send workouts, heart rate and GPS to Fuse directly — Strava is usually a mirror of that same data, not the source of it.

If you record workouts only on Strava and don't have a watch connected to Fuse, you can still keep your training score current by logging activities manually. Go to Enter Data Manually to log a run, ride, or session by type and duration — no device connection required.

Strava's API policy: strava.com/legal/api_policy

Does the Hume Body Pod work with Fuse?

Yes. The Hume Body Pod writes weight, body fat, and BMI to Health Connect. If you have Health Connect set up in Fuse, that data flows in automatically — no separate Hume account or login needed.

To enable it: open Health Connect on your Android phone, go to App access → Hume, and turn on Allowed to write for Weight, Body fat, and Body measurements. On Samsung phones: Samsung Health → Settings → Health Connect, then grant Hume write access.

I have a Hume Body Pod and Samsung Health — why doesn't Samsung Health show my body fat?

Samsung Health reads Hume body-composition data only if Health Connect has the right write permission set for Hume. Open Samsung Health → Settings → Health Connect, find Hume in the app list, and confirm Allowed to write is on for Body fat and Body measurements. Once that permission is active, your next Hume weigh-in will write to Health Connect and Fuse will pick it up on the next sync.

How do I open Health Connect on a Galaxy?

You don't have to go through Samsung Health. Open Phone Settings and search Health Connect. On many Galaxy phones it sits under Other. That's the same Health Connect as Samsung Health → Settings → Health Connect. Confirm two things: Samsung Health is writing sleep, heart rate, and steps, and Fuse is allowed to read those same types. Opening Fuse is what sends the data — the Health Connect screen itself does not.

Why does my workout have no heart rate?

A workout without heart rate is almost never something you did wrong — it usually means the data never reached us. There are three reasons it happens, and they have different fixes.

Your source isn't connected or isn't permitted. Heart rate reaches Fuse through whichever device recorded the session. If that device isn't connected, or the health permissions for heart rate aren't granted, the workout arrives as duration only. Check the integration in Settings, and on Android confirm Health Connect allows Fuse to read heart rate.

You recorded the session on something that wasn't measuring heart rate. A phone-tracked walk or a manually logged session has no heart-rate source behind it. Logging the session still counts toward your training — it just won't carry the heart-rate detail.

The device doesn't send heart rate during workouts. Not every device or connection reports continuous heart rate for a session, even when it reports heart rate elsewhere during the day. Where that's true for a specific device, we say so — we're building that per-device list from our own measured ingest data rather than from vendor marketing claims, and it will appear here as we confirm each one.

What is the ECG workout source setting?

Chest straps that measure the electrical signal of your heart (ECG) are more accurate during exercise than optical sensors on the wrist or finger, which are more affected by movement. If you train with an ECG chest strap, setting it as your workout source in Settings tells Fuse to prefer it for your sessions instead of averaging it with a less accurate reading.

This matters most for intervals and anything with rapid changes in effort, where optical sensors tend to lag. It applies to any session you wear the strap for — including mobility and stretching work, not just hard cardio.

If you don't use a chest strap, leave the setting alone. Fuse picks the most accurate source it has for each session on its own.

How does Fuse calculate my heart rate zones?

Fuse works out your five zones from your own numbers, not from a chart. Two inputs matter: your maximum heart rate and your resting heart rate. Your resting heart rate comes from your device each day. Your max starts as an age-based estimate, and once Fuse has seen a few genuinely hard workouts from you, it switches to the max it has actually observed in your own data — which is more accurate than any formula. From those two numbers Fuse sets your zone boundaries using the heart-rate-reserve method: it looks at the range between your resting and max heart rate, and places each zone as a slice of that range. Two people with the same max but different resting heart rates get different — correctly different — zones.

While Fuse is still estimating from age, your zones are labeled as estimates, and they can be off by around ±10 beats. One hard cardio session is the fastest way to sharpen them.

You won't see zones on strength, rehab, or mobility sessions. That's deliberate: heart rate is a poor measure of how hard lifting is (it climbs for reasons that have nothing to do with aerobic effort), so showing zone credit for a squat session would be telling you something false. You still see your average and peak heart rate for those sessions.

That automatic setup is the default, not the ceiling. In Settings → Training you can choose your zone method — heart-rate reserve or lactate threshold — and enter your own measured numbers, and every zone in Fuse will follow your choice. The questions below explain what the methods are, how to pick one, and how to get the numbers each one needs.

What's the most accurate way to set heart rate zones?

By the science, there's a clear ranking:

1. A real threshold test. Zones anchored to your lactate threshold — measured in a lab, by a watch that runs a guided threshold test, or with the 30-minute field test described below — are the gold standard, because the threshold is a real, measured feature of your body, not a percentage of anything. In Fuse, pick the Lactate Threshold method in Settings → Training and enter that number.
2. Zones computed from your measured max and resting heart rate. This is what Fuse does automatically. It's the best method that doesn't require a test.
3. Age formulas. "220 minus age" and its cousins miss the mark by ±10 beats or more for a typical person. This is what most devices use out of the box.

The uncomfortable truth about defaults: the most common setup on people's wrists — zones as percentages of an age-estimated max — is the least accurate of the three. Fuse never leaves you there once it has your data.

My watch already shows heart rate zones. Which zones should I trust?

It depends on where your watch's zones came from.

If you've done a threshold test — for example, some Garmin watches can measure your lactate threshold during a guided run and set your zones from it — those zones are anchored to your actual physiology, and they're better than anything computed from max and resting heart rate alone. Use them: pick the Lactate Threshold method in Settings → Training and enter the threshold heart rate your watch measured, and Fuse will build every zone from your number instead of its own.

If you've never done a threshold test, your watch is almost certainly showing its factory default — usually percentages of "220 minus age" — and Fuse's automatically computed zones will be more accurate. Let Fuse do it.

One honest limitation: watches don't send their zone settings to Fuse through our current data connections — we've verified this for Garmin, Oura, and Whoop, and the list of devices we've checked is growing. Some send how long you spent in their zones, but not the zone boundaries themselves. So if you want Fuse to use your watch's threshold-based zones, entering them in settings is the way to do it today.

Also expect Fuse's zones to differ from your watch's — each brand calculates zones its own way (different formulas, different bands), which is exactly why Fuse computes one consistent set across all your devices.

What is a heart rate zone, exactly?

A heart rate zone is a band of effort, marked out in beats per minute. Zones are not a score, and a higher zone is not a better zone — each band is a different training tool. The low zones build your aerobic base and let you accumulate a lot of training without wearing yourself down; the high zones sharpen speed and top-end fitness and are only sustainable in small doses. Exercise science writes its training guidance in these bands: the American College of Sports Medicine, for example, defines "moderate" and "vigorous" exercise as specific slices of your heart-rate reserve (Garber et al., 2011, ACSM Position Stand).

Zones are personal. Two people running side by side at the same pace can be in different zones, because a zone is defined by your physiology — your maximum, resting, or threshold heart rate — not by pace or by how hard the effort looks from outside. That's why Fuse asks for your numbers instead of reading them off a chart.

Why does Fuse ask me for my numbers instead of estimating them?

Because the estimate everyone knows — "220 minus your age" — is wrong by a lot, for a lot of people. Researchers who traced the formula's history found it was never derived from a rigorous study of maximum heart rate, and that formulas of this type carry a standard error on the order of ±10 beats per minute — which means roughly one person in three is off by more than 10 beats, and some by 20 or more (Robergs & Landwehr, 2002, Journal of Exercise Physiology online 5(2); Tanaka, Monahan & Seals, 2001).

A wrong ceiling doesn't produce one wrong number — it shifts every zone, because every boundary is computed from it. We've measured this with real data: one of our own testers had 185 stored as his max while his true max is 200. Every zone boundary sat about 7% low, and his easy sessions displayed as tempo work — the app was effectively telling him to back off on days he was training exactly right.

So Fuse treats formulas as a last resort, asks you for measured numbers where you have them, and gives you honest ways to get them where you don't — see "How do I find my resting heart rate, max heart rate, and LTHR?" below.

Reserve or Lactate Threshold — which method should I choose?

Fuse's zone calculator offers two computed methods (plus fully custom bounds if you already have zones you trust).

Heart-rate reserve (also called the Karvonen method) places five zones across the range between your resting and your maximum heart rate — your "reserve." It needs two numbers: max HR and resting HR. Because it accounts for your resting heart rate, it tracks your actual relative effort more faithfully than percentages of max alone (Karvonen, Kentala & Mustala, 1957; Swain & Leutholtz, 1997), and both numbers are easy to get — your wearable measures resting HR every night, and max can be observed from your own hard sessions.

Lactate threshold builds seven bands as percentages of your lactate threshold heart rate (LTHR) — roughly, the highest effort you can hold steadily for about an hour (Friel's zone guide on TrainingPeaks). Its strength is that the anchor is a real physiological event you measured, not an estimated ceiling, which is why it's generally the preferred method for trained endurance athletes. Its cost is that you have to measure it: a hard 30-minute field test, or a lab or watch-guided threshold test.

How to choose, honestly: a measured reserve setup beats a guessed threshold setup. If you haven't done a threshold test and don't want to, choose Reserve with real numbers — it is a good method, not a consolation prize. Choose Lactate Threshold when you have an actual measured LTHR, or you're willing to do the field test and re-test as your fitness changes.

One thing worth knowing: zone models genuinely disagree with each other. Researchers often work in three zones (Seiler & Kjerland, 2006), most consumer devices show five, and Friel's threshold system uses seven bands — and the exact boundary percentages differ between authors and brands. There is no single canonical banding. What matters most is that your zones are anchored to your own measured numbers and used consistently, which is what the calculator does: Fuse displays the band structure of whichever method you choose, the same way everywhere.

How do I find my resting heart rate, max heart rate, and LTHR?

Resting heart rate — the easy one. If you wear a device that measures overnight or morning resting heart rate, that's your source; the calculator's "Suggest my values" button reads it from your recent days and tells you where the number came from. Measuring by hand also works: first thing in the morning, before you get out of bed, count your pulse for a full 60 seconds; do it a few mornings and use the typical value (Harvard Health on resting heart rate).

Max heart rate — formula last, data first. Age formulas are the last resort (see above — typical error around ±10 beats). Your real max is the highest heart rate you actually reach in a genuinely hard effort, so if Fuse already has hard sessions from you, "Suggest my values" will offer the max observed in your own data, labeled with its source — no special test needed. A deliberate field test, if you want one, looks like: a long warm-up, then several minutes of progressively harder effort (a steady hill or repeated hard intervals) taken close to your limit — the highest reading is a good approximation of your max. A word on safety, because a max test is by definition an all-out effort: if you're new to vigorous exercise, returning from a long break or illness, or have a heart condition or symptoms like chest pain or dizziness during exercise, talk to a clinician before doing a maximal test — that's the standard pre-participation screening guidance (Riebe et al., 2015, ACSM). The observed-from-your-data suggestion requires no test at all.

LTHR — the 30-minute field test. The standard protocol comes from Joe Friel: ride or run a 30-minute time trial alone (not in a race, not with training partners), at a steady effort as if racing the full 30 minutes; press the lap button 10 minutes in; your LTHR is your average heart rate for the final 20 minutes (Friel's zone guide on TrainingPeaks). The most common mistake is starting too hard and fading — that skews the number, so pace it steady. Test per sport if you train both running and cycling; the two thresholds differ. Honest footnote: Friel's own site also describes a shorter variant — a 20-minute time trial, taking the whole-test average minus 5% (joefrieltraining.com). Both are approximations of the same threshold; the 30-minute version is the one our instructions follow. If you'd rather not test yet, the calculator's "Estimate from my data" button scans your stored workout heart-rate history for your hardest sustained 20-minute effort — the same statistic the field test measures — and tells you how confident it is in the result.

What actually changes in the app once I set my zones?

Everything that touches zones follows your configuration — and it all agrees with itself:

• The zone ranges you see and the minutes we count come from the same numbers. The beats-per-minute range printed next to each zone is exactly the range used to classify your time-in-zone, on the Output card, the cardio charts, and everywhere else.
• You see your bands, in beats per minute. Heart rate is measured in bpm in both unit systems, so nothing changes if you switch between Imperial and Metric. If you chose the Lactate Threshold method you'll see its seven bands where there's room in the display; compact charts group the three top sub-bands into one Zone 5.
• Your history follows your current method. Zones are a lens over your recorded heart-rate data, not part of the recording — so when you change method or update a number, past days are re-read under the new zones too. Your charts reflect your current method, which is why a session can move zones after you update your numbers: the data didn't change, your zones got more accurate.
• Suggested values are labeled. Anywhere Fuse suggests a number for you, it tells you whether it was observed in your data, read from your device, or estimated from a formula — so you always know how much to trust it.

My zones look wrong. What should I do?

The usual signs: sessions that felt easy and conversational register as tempo (Zone 3), or you can't reach the top zone even in an all-out effort. Both usually mean one input is off — most often a max or threshold that no longer matches your body.

Three steps:

1. Re-check the inputs, not the zones. Open Settings → Training and look at the numbers behind your method. Resting heart rate drifts with fitness, stress, and sleep, and training itself lowers resting heart rate over time — that was the finding of the original Karvonen study (Karvonen, Kentala & Mustala, 1957). A resting value from months ago may simply be stale.
2. Re-measure or re-estimate. Use "Suggest my values" or "Estimate from my data" to pull fresh numbers from your recent history, or re-run the field test for the number you suspect (see the question above). If your training has changed markedly — much fitter, or coming back from time off — a re-test is the honest fix; thresholds and resting heart rate move with fitness in both directions.
3. Save, and let everything recompute. Updating a number updates every zone surface, including your history, so the fix is visible immediately — you don't need to re-log or edit anything.

If you've re-tested and something still looks off, tell the coach what you saw — a session name and what felt wrong is enough for us to check the data behind it.

Why does a workout sometimes show at the wrong time of day?

Your devices don't all record time the same way. Some send us the time in your local clock along with which time zone they think you were in; others send the time in a single world-standard clock and leave the time zone to us. Most of the time both arrive at the same answer.

Occasionally a device gets the time zone part wrong — it records the right clock time but labels it with the wrong zone. When that happens the workout can land a few hours off, and if it was late in the evening or early in the morning it can even land on the neighbouring day.

Nothing is lost when this happens, and it doesn't change how hard the workout counted. If you spot a session sitting at a time you know you weren't training, tell the coach — mentioning the day and roughly when you actually trained is enough for us to line it up.

Why did the same workout appear twice?

If two of your devices both recorded the same session, and they disagree about what time zone you were in, we can end up treating one workout as two. It's the same cause as the question above: the two records look hours apart even though they describe the same hour of your day.

You don't need to delete anything. Tell the coach which session was doubled and we'll merge it.

How do I connect my device to Fuse?

It depends on what you have. Most connections take under a minute, and you only do each one once.

iPhone and Apple Watch: Fuse reads Apple Health. Open Fuse, go to Connected Devices, tap Connect next to Apple Health, and allow the data types iOS asks about. Open Fuse once a day — opening the app is what sends your latest data across.

Android phone: Fuse reads Health Connect. Open Fuse, go to Connected Devices, tap Connect next to your Android health data, and allow the types Health Connect asks about. Whatever writes to Health Connect — your watch, your scale, Samsung Health — reaches Fuse the same way.

Samsung Galaxy: see "How do I open Health Connect on a Galaxy?" above. You don't have to go through Samsung Health.

Oura, Whoop, Garmin, Polar, Withings, TrainingPeaks, MyFitnessPal, Google Fit: open Fuse, go to Connected Devices, tap Connect next to the one you have, and sign in to that account when the window opens.

Hevy or Intervals.icu: these use an API key you copy from their own app. Fuse shows you exactly where to find it — Connected Devices, then Direct Integrations.

Strava: not supported, and that's a policy limit rather than a technical one. See "Does Fuse work with Strava?" above.

If your device isn't on this list, connect the phone instead — Apple Health and Health Connect between them carry data from most watches, rings and scales, including ones we don't connect to directly.

My data stopped updating. What do I check first?

Open the Fuse app. That is genuinely the first step: opening the app is what pulls your latest data across, so a phone that hasn't had Fuse opened in a few days looks exactly like a broken connection when it isn't.

If your data is still behind after opening Fuse, check that the app you sync from has actually recorded the day — Apple Health, Health Connect, or the device's own app. If it has and Fuse hasn't caught up, write to us at hello@fuse.fit and tell us the date you're missing. We can see what arrived and what didn't.