Know exactly
what to train next.
Watts tell you what you did. Your blood tells you what it cost. Lactate Engine turns one finger prick into decisions you can act on tomorrow morning.
your real threshold
Three questions your watts can't answer
Power meters measure the output. They say nothing about the cost. That cost is what decides your next session.
"Is 250 W really my threshold?"
An FTP test gives you a number from a good day. Your blood gives you the point where lactate stops being cleared as fast as it appears — and they are rarely the same.
You stop riding your endurance days 15 W too hard — every single week.
"Should I go hard today?"
Sleep, HRV and resting heart rate come in from Apple Health on their own, and land next to your training load — cycling and running kept apart.
You spend your hard days when they will actually stick.
"Why do I fade after three hours?"
Fresh thresholds are the easy half. The durability test measures what you keep after 2–4 h — the number that decides a col, a marathon or a duathlon.
You train the thing that actually costs you the finish.
What changes in your week
Not more graphs. Different decisions.
How it works
One afternoon of testing, then it runs with your normal training.
Ride the protocol
Export the test to your Garmin. Press lap at each stage. The app reads the laps back and fills the table for you.
Add the drops
Type or dictate each lactate value. Ten numbers, one afternoon.
Get your zones
LT1, LT2, threshold pace or power, and the sessions that follow from them.
Keep it honest
A prick on a normal ride tells the app whether it still has you right.
Your lactate, live on the bike
The Connect IQ data field runs the same model on your Edge or watch — modelled lactate and its uncertainty band while you ride. Press lap when you prick: the app matches the sample to the second.
The loop that makes you faster
Blood work is only worth it if it changes something. This is what closes the circle.
Four protocols: incremental, reverse, durability, clearance.
Thresholds, readiness and load turn into one recommended session.
Samples on real rides show measured against predicted — and correct the model.
It tells you when it doesn't know
Every number carries the method that produced it, the test it came from, its age and its uncertainty band. When two published methods disagree by more than 15 W, the app says so instead of picking one quietly. Field samples can bend the curve — they can never move your thresholds on their own.
Everything in the app
For the physiologists — the methods behind the numbers
LT1 — log-log double regression (Beaver, Wasserman & Whipp 1985), split chosen by minimum residual sum of squares.
LT2 — Dmax on a least-squares cubic fit: modified chord (Bishop 1998) by default, classic first-to-last chord (Cheng 1992) and the discrete stage pick available; the driver is yours to choose, and all three are shown side by side. P@4 mmol/L (Heck 1985) and an MLSS proxy come with them.
Session model — per-sample simulation on 30-second smoothed power, with glycolytic, fatigue and terrain terms, an uncertainty band, and re-anchoring on every measured sample.
Recalibration — weighted median of measured/predicted per zone, shrunk toward 1 and clamped to [0.6, 1.6]; durability and clearance fitted separately; thresholds, time constant and glycolytic factor are never touched.
Running — grade-adjusted pace from Minetti et al. 2002, normalized graded speed, rTSS with an hrTSS fallback. Running never borrows cycling thresholds or maximum heart rate (Roecker 2003).
Free to start
Apple Health import · FIT, TCX and CSV files · incremental test · thresholds with their method · session analysis · readiness · planner · Garmin workout export
All four protocols · field samples and recalibration · durability and clearance engines · climb predictor · duathlon planning · Garmin sync · PDF reports
Premium scope is indicative until launch. Subscriptions are handled by Apple and cancellable any time.
One test. Then you stop guessing.
Ten stages, ten drops of blood, one afternoon — and every session after it has a reason.
Download on the App Store