Guide
Intervals.icu for Cycling — FTP, Power Zones, and Sync
Intervals.icu is one of the few free services where serious cycling analytics (TSS, CTL, IF, NP, power curve) work out of the box. This guide walks through FTP testing, Coggan/Friel zone setup, loading activities from Garmin and Wahoo, and debugging duplicates.
What Intervals.icu Gives a Cyclist
If your Garmin or Wahoo has a power meter, Intervals.icu turns those numbers into a working training system. Not just a log — a fitness tracker, interval analyzer, and planner.
Normalized Power, Intensity Factor, TSS, VI, time-in-zones — all out of the box. Month / year power curve. Compare segments and workouts in W/kg.
CTL (chronic load), ATL (acute), TSB (freshness). For a cyclist, this is the primary tool for peaking to a race or brevet.
Structured workouts (SST, 4×8, VO2 intervals) built in the calendar and sent to Garmin / Wahoo / Karoo. On the head unit — ready-made structure with wattage targets.
Step 1
FTP Test and Zone Setup
FTP (Functional Threshold Power) is the anchor number that all zones are calculated from. Intervals.icu can estimate FTP automatically from rides (Auto FTP), but for an accurate start, a dedicated test is better.
Warm up for 20 minutes
Easy riding with a couple of 1-minute surges in the middle. Key thing — don't acidify before the main effort.
20-minute maximum test
A steady, maximally stable 20-minute effort. Record the average power. Best format — on a trainer or a flat road / climb with no stoplights.
Multiply by 0.95
That's your FTP. For example, 220W × 0.95 = 209W. Enter this value in Settings → Power → FTP. Intervals.icu will recalculate all zones and metrics from that moment.
Coggan zones (% FTP): Z1 Recovery (<55%), Z2 Endurance (56-75%), Z3 Tempo (76-90%), Z4 Threshold (91-105%), Z5 VO2max (106-120%), Z6 Anaerobic (121-150%), Z7 Neuromuscular (>150%). This is the default — Intervals.icu lets you use Friel, Polarized, or custom zones.
Step 2
Connecting Garmin and Wahoo
Intervals.icu doesn't read directly from the power meter — it pulls finished activity files from Garmin Connect, Wahoo, Strava, and Dropbox. Connect once, then sync is automatic.
Settings → Integrations → Garmin → Connect. OAuth authorization. All rides (new ones and the last 30 days) arrive within 15 minutes of uploading to Garmin Connect.
Wahoo has no direct integration — it routes through Strava. Enable Auto-sync from Wahoo in Strava, then Connect Strava in Intervals.icu. A ride shows up in both services.
Hammerhead Karoo 2/3 uploads FIT files to Intervals.icu directly. On the Karoo: Sync Providers → Intervals.icu.
If no direct integration — use the Upload button on the homepage. You can bulk-upload an archive of old workouts to build a retrospective CTL.
Workouts: Building Sessions in Watts
Unlike running, where the target is pace or HR, the cycling standard is watts. Intervals.icu builds workout structure directly from text.
SST 2×20
Warmup 15min 60% → 2 x (20min 85-88% FTP, 10min 55%) → cooldown 10min. Save, push to Garmin / Wahoo. On the head unit every interval is highlighted with wattage target.
VO2 5×4
Warmup 15min → 5 x (4min 108-115% FTP, 4min 50%) → cooldown. After the ride Intervals.icu shows time-in-zone, average power per interval, drift.
Endurance ride
Pure Z2 time (60-75% FTP) — 2-4 hours. No intervals, but checked — not drifting into Z3. Base volume for brevets or Ironman.
Common Issues
If test FTP came in lower than expected, check zero-offset on pedals / crank / hub. Older meters drift — calibrate monthly.
If FTP is underset (e.g., an old value after a winter break), TSS will be inflated — workouts look heavier than they are. Enable Auto FTP or update manually after a good test.
If HR rose 10+ bpm mid-ride at stable power, that's not a bug — that's cardiac drift: a sign of heat, underfueling, or overtraining.
FAQ
Do I need a power meter for Intervals.icu?
No — HR zones work too. But all the signature power analytics (NP, IF, TSS, power curve) only unlock with watts. For meaningful CTL/TSB you need at least a single-side power meter or a smart trainer.
How often should I retest FTP?
Every 4-6 weeks in an active phase. Auto FTP in Intervals.icu recalculates the estimate from your best 20-minute efforts in real rides — enough for many riders.
20-minute test vs ramp test?
20-minute is more reliable — less influenced by anaerobic power. Ramp is simpler and shorter (15-20 min total), but it overestimates FTP for sprinters and underestimates for endurance riders.
Is Intervals.icu better than TrainingPeaks for cycling?
On core analytics (NP, TSS, CTL, power curve) — comparable. Intervals.icu is free and ships new features faster (HRV Status, sleep integration). TrainingPeaks is stronger in coach-athlete workflows for large teams and plans from pro coaches.
Where do I upload the FTP test without Garmin?
Zwift auto-syncs to Strava → Intervals.icu. Wahoo KICKR writes a FIT file that can be uploaded manually. TrainerRoad also sends to Strava and on to Intervals.icu.
Does it work for gravel / MTB?
Yes — TSS relies on power, not pace, so terrain and surface don't skew the numbers (unlike running). FTP training works the same on pavement, gravel, or dirt.
Related
Intervals.icu Data → AI Coach for Cycling
STAS connects Intervals.icu to ChatGPT and Claude. AI sees your FTP, history, CTL — and writes plans in watts, not in abstractions.
Connect Intervals.icuFree — no subscription