Indoor training with heart rate only (no power meter, no problem)
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You don't need a power meter to train properly indoors — you need a signal you can trust, and a heart-rate strap is one. HR is a lagging signal, and it wobbles with heat and sleep and coffee, but it has one great virtue: it can't be fooled about how hard your body is actually working. Generations of riders built serious fitness on nothing else. Here's how to set your zones from one honest test, what HR is genuinely good and bad at, and a week of sessions you can ride tonight.
- Find your LTHR with a 30-minute solo time trial: your average HR over the final 20 minutes is your threshold heart rate. Every zone hangs off that number.
- Play to HR's strengths: steady endurance and long intervals, where the lag doesn't matter. Pace anything under ~3 minutes by feel instead.
- Indoors, a fan is training equipment: without airflow your HR drifts upward from heat, not effort, and every zone quietly lies.
Why HR still works
Heart rate is your cardiovascular system reporting its own workload in real time. It lags effort — the pump takes 30–90 seconds to catch up with the legs — and it's nudged around by temperature, hydration, sleep and stress. But over any effort longer than a few minutes it's an honest, personal measure of internal load, which for building aerobic fitness is precisely the thing you're trying to train. Power tells you what you did to the pedals; HR tells you what it cost. For most of the training that actually makes you faster — patient, repeatable aerobic work — the cost is the number that matters.
Step one: find your LTHR
Forget "220 minus age" — it misses real individuals by 10–20 bpm in either direction. The anchor you want is your lactate threshold heart rate (LTHR), found with one honest field test:
- Warm up 10–15 minutes, finishing with a couple of short hard bursts.
- Ride 30 minutes flat out — the hardest pace you can sustain for the full half hour, solo, no sprint finish. Start your HR recording at the start.
- Your LTHR is the average HR of the final 20 minutes. The first 10 minutes are excluded precisely because HR is still climbing to meet the effort.
Pace it like a time trial: the classic mistake is flying for 8 minutes and wilting for 22, which drags the average down and sets every zone too low. Done indoors with a good fan, it's very repeatable — retest every 6–8 weeks.
Your five zones from LTHR
Percentages below are of LTHR, not max HR, and they're approximate — bands, not tripwires. Your body doesn't change gear at a boundary:
HR zones as a share of LTHR
% of LTHRSegment widths are illustrative, not to scale. The talk-test descriptions are the real-world check — if the feel and the number disagree wildly, retest your LTHR.
What HR does well — and where it lies to you
Steady endurance riding
Z2 work is HR's home turf. The effort is long and stable, so the lag doesn't matter — HR settles in and tells you honestly whether you're drifting too hard.
Long intervals (8+ minutes)
Tempo and threshold blocks are long enough for HR to catch up and level off. Cap the effort at a target HR and the interval polices itself.
Keeping easy days easy
The most valuable job of all. A hard HR ceiling on recovery rides stops the slow creep into the grey zone that wrecks training weeks.
Short intervals (under ~3 minutes)
HR lags effort by 30–90 seconds, so by the time it reflects a 1-minute effort, the effort is over. Pace short work by feel (RPE) and cadence instead — the strap just records.
Day-to-day comparison
Heat, caffeine, poor sleep, stress and dehydration all shift HR by 5–10 bpm at the same effort. Treat any single ride's numbers with a pinch of salt; trust the trend.
Measuring improvement precisely
A lower HR at the same feel suggests progress, but HR can't tell you your output rose 3%. That precision is what power is for.
Cardiac drift, and why your fan is training equipment
Ride steadily indoors and your HR will slowly climb even though the effort hasn't changed — cardiac drift. As you heat up, blood is diverted to the skin for cooling and sweat trims your plasma volume, so the heart beats faster to move the same oxygen. Indoors this is dramatically worse than outside, because there's no 30 km/h headwind doing your cooling for you. A proper fan (or two) is the difference between drift of a few beats and drift of fifteen — and between an honest Z2 session and one where "Z2 heart rate" quietly becomes Z1 output. Point it at your torso, start it before you're hot, and treat modest drift late in long sessions as normal rather than a licence to ease off completely.
A sample HR week — three sessions
Endurance builder
Settle at 81–89% of LTHR and hold it. If HR drifts above the band at the same effort, ease off — that's the session working, not failing.
Tempo intervals
3 × 12 min at 90–93% of LTHR with 5 min easy between. Let each interval's first 2 minutes run slightly warm on feel while HR catches up.
Threshold touches
2 × 15 min building to 94–99% of LTHR. Start each block by feel, then steer by HR once it stabilises around minute 3.
Space them out with at least a day between the two harder sessions, and add easy Z1–Z2 riding around them as time allows. Consistency across weeks beats heroics in any single one.
When power becomes worth it
HR-only training hits its ceiling when you want short, sharp work (VO2max intervals, sprints) measured properly, or when you want to see fitness changes in hard numbers rather than feel. The cheap paths to watts: used power-meter pedals or a used crank meter (from roughly €250), or a used direct-drive smart trainer (from roughly €250–400) which adds ERG mode into the bargain. When you get there, our FTP guide is the next read. Until then, nothing is blocking you: Moveee Indoor pairs any standard Bluetooth HR strap straight from the browser (Chrome or Edge, nothing to install) and runs HR-based sessions on real 3D roads, free, with the ride saved to Strava. A €35 strap and an honest half-hour test, and you're training with structure tonight.
Sources 6
Where this article summarises a study, the study itself is linked — not a write-up of it.
- 1 Achten J, Jeukendrup AE Heart Rate Monitoring: Applications and Limitations · Sports Medicine · 2003
- 2 Tanaka H, Monahan KD, Seals DR Age-predicted maximal heart rate revisited · Journal of the American College of Cardiology · 2001
- 3 Coyle EF, González-Alonso J Cardiovascular Drift During Prolonged Exercise: New Perspectives · Exercise and Sport Sciences Reviews · 2001
- 4 González-Alonso J, Mora-Rodríguez R, Below PR, Coyle EF Dehydration markedly impairs cardiovascular function in hyperthermic endurance athletes during exercise · Journal of Applied Physiology · 1997
- 5 Persinger R, Foster C, Gibson M, Fater DCW, Porcari JP Consistency of the Talk Test for Exercise Prescription · Medicine & Science in Sports & Exercise · 2004
- 6 Borszcz FK, Tramontin AF, Bossi AH, Carminatti LJ, Costa VP Functional Threshold Power in Cyclists: Validity of the Concept and Physiological Responses · International Journal of Sports Medicine · 2018
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