Training with a Hammerhead Karoo: getting a real plan onto the bars

What the Karoo does once it has a workout

It renders the session properly and gives you real control over it. Workouts can be sorted by newest, TSS, or duration, and before starting one you can see which zones it targets and how long you will spend in each [Hammerhead Karoo Workouts]. The gap is upstream of all of this.

The workout drawer is customizable per ride profile, the same way the rest of the Karoo's pages are. You choose which data fields appear while a workout is active, and you can show the target as a visual field, as a numeric one, or turn it off entirely [Hammerhead Karoo Workouts]. Three dedicated control fields can be added to any profile: workout control for skipping and rewinding intervals, workout scale for raising or lowering intensity, and workout pause. The pause is genuinely independent — you can pause the workout without pausing the ride, while pausing the ride pauses both, including under auto-pause.

One detail deserves more attention than it gets, because it changes what your ride file is worth afterwards. The Karoo automatically starts a new lap at the beginning of every workout interval, and pressing the lap button yourself does not disturb the workout at all — it simply records another lap [Hammerhead Karoo Workouts]. The consequence is that a Karoo-recorded interval session arrives with its structure already marked. Any analysis reading that file can report what you actually held on rep four rather than inferring rep boundaries from a power trace, which is guesswork on a ride with variable terrain.

You can also add a workout to a ride already in progress. It counts as a new workout and has to be started from the workout page, while the Karoo keeps recording the session as one continuous effort [Hammerhead Karoo Workouts]. That is the right behaviour for a rider who decides at the turnaround that the day is going better than expected.

None of this touches the question of whether today's session is the correct one. The device faithfully renders a decision that something upstream already made. When a plan on a Karoo stops making sense after a heavy weekend or a week off, the delivery layer worked exactly as designed — the fault is in the layer that never revisited the decision.

Where workouts come from, and why the popular answer is out of date

Search this question and nearly every result says TrainingPeaks. That was true for years and is no longer the whole picture. Hammerhead's Dashboard now links to ten third-party accounts, accepts direct file uploads, and the device pulls new workouts the next time it reaches the internet [Hammerhead Account Linking, Hammerhead Workout Import].

The old constraint is still quoted in Hammerhead's own documentation, which is a large part of why it persists. The smart-trainer article still carries the line: currently, only workouts synced from Training peaks or uploaded to the Dashboard in a .FIT or .ZWO file will work [Hammerhead Trainer Support]. The Workouts article, updated more recently, states it more broadly — workouts can be imported from your connected third-party accounts or through the Dashboard [Hammerhead Karoo Workouts]. Both are Hammerhead's; they disagree; the second is the current one. A rider who lands on the first reasonably concludes the door is still shut.

What the Dashboard actually links to today is a longer list: AXS, Intervals.icu, Komoot, Ride with GPS, Sentiero, Strava, Suunto, TrainerRoad, TrainingPeaks, and Xert [Hammerhead Account Linking]. Not all of those send workouts — several are route or activity destinations — but the set is no longer a single name, and Intervals.icu in particular closed a feature request that had been open since 2021. Treat any page that still says TrainingPeaks-only as evidence of when it was written.

The manual route is the one most riders overlook, and it has no subscription attached to it at all. The Dashboard imports .ZWO and .FIT workout files directly — add the workout, and the next time your Karoo connects to the internet it syncs across [Hammerhead Workout Import]. If a platform can export a structured workout as a file, it can reach your Karoo, whether or not it appears on any partner list.

Worth naming the cost of that route honestly: a file you upload by hand is a snapshot. It does not update when your week changes, and doing it daily is a chore that quietly stops after a fortnight. The manual path proves the device is not locked down. It does not solve the problem of keeping a plan current.

The import rules nobody writes down

Hammerhead publishes exactly what its importer accepts, and the rules are stricter than most workout exporters assume. A file that breaks any of them is rejected outright rather than partially imported [Hammerhead Workout Import]. This is the source of most mystifying import failures.

For .ZWO files, every step must be a warmup, cooldown, free ride, repeating interval, or steady state. Maximum-effort and ramp steps are explicitly unsupported [Hammerhead Workout Import]. Every step must also carry at least one target — power, a power range, cadence, or a cadence range — and where both power and cadence are supplied, power wins. Zone-based power targets are not supported at all, so a workout expressed as ride zone 4 for ten minutes rather than as a percentage will not import.

The .FIT rules are different in a way that matters more than it first appears. A FIT workout's steps may target speed, heart rate, cadence, or power — heart rate and power as absolute values or percentages, speed and cadence as absolute values only [Hammerhead Workout Import]. Heart rate is on that list. It is not on the ZWO list. The two formats are therefore not interchangeable: the same session exported as ZWO carries power and cadence only, and exported as FIT can carry heart rate. If your targets are heart-rate based, the format you choose is the whole question.

Two smaller rules catch people out. Distance-based workouts are not supported and are converted to time-based ones on import [Hammerhead Workout Import]. And a FIT file that is an activity or a route rather than a workout is rejected — an easy mistake, because all three share an extension and a rider exporting from an analysis platform often has all three available.

The practical takeaway for choosing a provider is that structured-workout export is not a single capability. A platform that exports ZWO can reach your Karoo with power targets. A platform that exports FIT workouts can reach it with heart-rate targets. A platform that only publishes to its own calendar can reach it only if Hammerhead lists it.

Structured training without a power meter

Harder on a Karoo than on some rivals, and worth understanding before you buy into a plan. Hammerhead states plainly that RPE-based workouts are not supported [Hammerhead Karoo Workouts], and following a workout requires a trainer or sensors that can report your effort against the target.

That rules out one common fallback. On some head units a workout can prescribe an interval by perceived exertion, which lets a rider with neither a power meter nor a heart-rate strap follow the structure of a session. The Karoo does not offer that route, and it needs a smart trainer or sensors reporting effort against the selected workout in order to follow one at all [Hammerhead Karoo Workouts].

The route that does work is heart rate, delivered as a FIT workout. FIT steps accept heart-rate targets as absolute values or percentages [Hammerhead Workout Import], so a rider with a strap and no power meter can run genuinely structured intervals. The structure, the interval boundaries, the automatic laps, and the on-device controls all behave the same way. What changes is the precision of the target, not the availability of the session.

Heart-rate targets need one physiological adjustment read into them. Cardiovascular drift raises heart rate over prolonged exercise even when work rate is held constant [Coyle & González-Alonso 2001]. On a long session, that means the later intervals ask you to reach a number your body is already producing at a lower power output, so satisfying the target late in a workout is not the same achievement as satisfying it early. Power targets are immune to this; heart-rate targets are not, and a plan built on them should be read with that in mind.

ERG, ANT+ FE-C, and why a target set too high fails late

The Karoo controls a trainer over ANT+ FE-C — and Hammerhead notes that not all smart trainers use it [Hammerhead Trainer Support]. Once paired, ERG holds the prescribed watts no matter what you do with the pedals, which is simultaneously the feature and the failure mode.

The control surface is better stocked than most riders realize. While following a workout you can switch between ERG, where targets adjust up or down in 1% increments, and Read-Only, which records power from the trainer without controlling it — so the Karoo becomes a display and recorder while another platform drives the trainer [Hammerhead Trainer Support]. Outside a workout there are four modes: ERG in 5-watt steps, Resistance as a percentage of the trainer's maximum, Grade in 1% increments, and Read-Only. Spindown calibration runs from the Control Center.

The reason a slightly-high target fails late rather than early is physiological, not psychological. Work above critical power draws down a finite capacity, W-prime [Jones et al. 2010], which only reconstitutes below that intensity [Skiba et al. 2012]. ERG removes the self-selection that would otherwise have shed a few watts on rep two, so each rep drains slightly more than the recovery restores. Nothing feels wrong until the reservoir is empty, which arrives several reps in rather than at the start — long after the point where adjusting would have saved the session.

That is what the scale control is for. A session completed at 95% of target is training; a session abandoned on rep five is a data point about your threshold setting and nothing else. And the threshold itself is a likelier culprit than most riders assume: measured against maximal lactate steady state, FTP tracks the group average closely but its 95% limits of agreement run to roughly 9% [Borszcz et al. 2019], and critical power and functional threshold power do not equate even in highly-trained athletes [McGrath et al. 2021]. A target you cannot hold may be a wrong number rather than a bad day.

It is also worth not treating ERG as the superior way to ride. Variable and constant power output at matched averages produce measurably different physiological responses [Kolsung et al. 2020], and Read-Only mode exists precisely so the Karoo can record a session it is not dictating.

What has to sit on top of the hardware

Everything above is delivery, and the Karoo does it well. The gap in the ecosystem is adaptation: nothing between a training calendar and the handlebars notices that Saturday's unplanned four hours changed what Tuesday should be, because Hammerhead never built a platform whose job that was.

The honest read on the providers. TrainingPeaks has the deepest structured-workout builder available and is the default for coached athletes. Intervals.icu offers genuinely strong analysis for free and now syncs directly. Xert and TrainerRoad both market adaptation, and both are worth a look if that is what you are after — each adjusts what it prescribes as your training changes, within the scope it was built for. Each is good at what it was built for. What none of them was built to do is rebuild the next fortnight around the week you actually had, outdoors, on the rides you actually did.

Keeping one ledger matters more than which tool you pick. The same rider produces different numbers indoors and outdoors — in matched-perceived-exertion 40-km trials, riders averaged 208 W outdoors against 163 W indoors, with higher heart rates outdoors too [Mieras et al. 2014]. Split your record across an indoor app and an outdoor one and no system holds the whole picture, which means nothing is checking the thing that actually decides whether a training year works: whether the easy rides stayed easy and the hard ones stayed hard [Seiler 2010].

That is the layer AdaptCycling is built for. We read your ride history from the source you already use, estimate threshold from your power curve rather than asking you to schedule a test [Jones et al. 2010], build a plan from what you have actually been doing, and revise it when the week goes sideways. Rides recorded on a Karoo arrive with their interval laps intact, so the analysis reports what you held rep by rep instead of estimating it.

Two limits stated plainly, including one of ours. A rolling window of upcoming days is what any provider can put on a head unit — nobody can place week nine on your bars today, and a tool claiming otherwise is describing its own calendar rather than the device. And the format constraint above is real: a workout delivered as ZWO carries power and cadence targets only. Our own Karoo push emits ZWO, so until we ship a FIT workout encoder a rider training to heart rate is better served uploading a FIT workout to the Dashboard than waiting on us.

Quick answers

Sources cited in this guide

1. 01
   Hammerhead Karoo Workouts. Karoo OS - Workouts. Hammerhead Support.
2. 02
   Hammerhead Workout Import. Dashboard - Importing ZWO & FIT based Workouts. Hammerhead Support.
3. 03
   Hammerhead Trainer Support. Karoo OS - Smart Trainer Integration. Hammerhead Support.
4. 04
   Hammerhead Account Linking. Dashboard - Linking Third-Party Accounts. Hammerhead Support.
5. 05
   Jones et al. 2010. Critical power: implications for determination of VO2max and exercise tolerance. Medicine & Science in Sports & Exercise.
6. 06
   Skiba et al. 2012. Modeling the expenditure and reconstitution of work capacity above critical power. Medicine & Science in Sports & Exercise.
7. 07
   Borszcz et al. 2019. Is the functional threshold power interchangeable with the maximal lactate steady state in trained cyclists?. International Journal of Sports Physiology and Performance.
8. 08
   McGrath et al. 2021. Do Critical and Functional Threshold Powers Equate in Highly-Trained Athletes?. International Journal of Exercise Science.
9. 09
   Kolsung et al. 2020. Physiological Response to Cycling With Variable Versus Constant Power Output. Frontiers in Physiology.
10. 10
    Mieras et al. 2014. Physiological and psychological responses to outdoor vs. laboratory cycling. Journal of Strength and Conditioning Research.
11. 11
    Seiler 2010. What is best practice for training intensity and duration distribution in endurance athletes?. International Journal of Sports Physiology and Performance.
12. 12
    Coyle & González-Alonso 2001. Cardiovascular drift during prolonged exercise: new perspectives. Exercise and Sport Sciences Reviews.

Specific questions inside this topic

Focused reads — each answers one question end-to-end.

1. 01

   Karoo structured workouts without TrainingPeaks

   TrainingPeaks is not required, and Hammerhead's own docs are part of why people think it is. The free upload route and the providers that qualify.

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2. 02

   Training plan apps for the Hammerhead Karoo

   Hammerhead ships no training platform, so the app you connect is the plan. What TrainingPeaks, TrainerRoad, Intervals.icu and Xert each actually do.

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3. 03

   Intervals.icu to Karoo workout sync: how it works

   The official sync landed in January 2025 and is created from the Karoo itself. What syncs, what the importer rejects, and the format trap.

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4. 04

   Karoo workouts not syncing: how to find the real fault

   Check the Dashboard first — that one look halves the problem. The provider rules that block a push, the device half, and the failure that is not one.

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5. 05

   ZWO file not importing to a Karoo: the rejection rules

   Hammerhead rejects the whole file, not the bad step. The step types it accepts, the target rule, and the difference between rejected and ignored.

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6. 06

   Karoo structured workouts without a power meter

   A heart-rate strap satisfies the Karoo's sensor requirement, but heart-rate targets exist only in FIT. What HR can target, and what it cannot.

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Related guides

• Training with Wahoo: a self-coached cyclist's guide →
• FTP without a test: estimating threshold from real rides →
• Adaptive cycling training plans that survive real life →