How accurate are running watch lactate threshold estimates?

Not very. Research found watches overestimated threshold pace by 13% to 26% on average, while heart rate estimates were closer but still off by six to seven percent—enough to put you in the wrong training zone. The pace figure is less reliable than the heart rate one.

Why does my lactate threshold estimate keep dropping even though I'm training consistently?

Heat, fatigue, illness, or altitude all raise your heart rate at any given pace, making the watch think your threshold is lower when it's really just your body responding to stress. If it drops after one hard session, that's noise—real improvement or decline takes weeks to show up.

Do I need a chest strap for my watch to estimate lactate threshold properly?

You don't absolutely need one, but it helps. Wrist-based optical sensors lag slightly and pick up noise during hard efforts, which can throw off the algorithm's reading. A chest strap gives cleaner, more accurate heart rate data.

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Your Watch Doesn't Know Your Lactate Threshold (But It Has a Decent Guess)

What lactate threshold actually means, how sports watches estimate it without blood samples, why they're often wrong, and what you should actually do with the number.

1 November 20269 min read