SomviaWhat threshold is, and why everything hangs on it
Threshold is roughly the hardest effort you could hold for an hour: above it, fatigue accumulates quickly; below it, you can keep going. Coaches use it as the anchor for training zones, and most training-stress models normalise against it, which means an error in your threshold quietly propagates into your zones, your session scores and the recovery time you are told to take.
The reference method is a laboratory lactate test. The practical method, used for decades, is a hard time trial: hold the best pace you can for twenty or thirty minutes and read the result. Somvia looks for efforts of that shape in what you have already run.
How it is estimated from your history
Inside each session, Somvia looks at the twenty and thirty minute stretches you covered fastest, and asks whether the heart rate over that stretch was high enough for it to have been a real effort. Every easy run contains its own fastest twenty minutes; counting those would drag the estimate down week after week, so only stretches run at a genuinely hard heart rate qualify.
Across the qualifying efforts of the last few months, the best one sets the estimate. Where a thirty-minute effort exists it is used directly, following Friel's convention; otherwise a twenty-minute effort is scaled down, following the convention that came out of Coggan's testing protocol. The two definitions are close but not identical, and Somvia picks one rather than taking whichever is higher, because a number inflated by a couple of percent moves every zone with it.
No qualifying effort, no number. If your last months have been entirely easy, Somvia shows the threshold row as waiting rather than printing an estimate built from easy running.
Threshold heart rate
Heart rate lags effort by a few minutes, so the average over a whole thirty-minute effort sits below the heart rate you were actually holding. The convention, again from Friel, is to read the last twenty minutes of the effort and drop the opening climb. Somvia does that, and reports the result next to the pace, since one is useful on the road and the other on a treadmill or a hill.
Critical power, for rides
Cycling with a power meter allows a cleaner version of the same idea. Your best power over a few durations in the two to fifteen minute range falls on a line whose slope is the power you could sustain, in the hyperbolic model published by Monod and Scherrer in 1965. Somvia fits that line when three usable durations exist and reports the result in watts and watts per kilogram; with fewer, it reports nothing rather than a line drawn through two points.
Where the method comes from
The twenty and thirty minute conventions, the heart-rate reading window and the critical-power fit are all published methods, listed with their sources on how the scores work.
Questions
Can I estimate lactate threshold without a lab?
You can estimate it, not measure it. A hard sustained effort of twenty to thirty minutes is the long-standing field proxy, and Somvia looks for efforts of that shape in the workouts already in Apple Health rather than asking you to schedule a test.
Why does Somvia show no threshold?
Because the recent record contains no effort hard enough to qualify. Every easy run has a fastest twenty minutes, and counting those would produce a number that falls a little further every month. One hard sustained effort is enough to produce an estimate.
Is threshold pace the same as my race pace?
It is close to a strong hour of racing, so it sits near ten-mile to half-marathon pace for many runners, faster than marathon pace and slower than 10 km pace. Predicted times for specific distances are estimated separately.
Does the estimate work for cycling?
For rides with a power meter, Somvia estimates critical power instead, which answers the same question in watts. Rides without power do not produce a threshold estimate.