Lactate Threshold Heart Rate (LTHR)
LTHR (Lactate Threshold Heart Rate) is your heart rate around the lactate threshold: the effort you can just about keep up in a controlled way for a long time. For many athletes it is a more reliable anchor for heart-rate zones than formulas based on your maximum heart rate.
What is LTHR?
Where threshold pace and FTP describe your output (pace, power), LTHR describes the internal load that goes with it: how hard your heart is working for it. Anchoring zones on LTHR has a big advantage over the classic "220 minus your age": the spread in maximum heart rate between people of the same age is enormous, whereas a measured threshold heart rate is genuinely yours.
LTHR differs by sport. In cycling the threshold heart rate is usually lower than in running, because less muscle mass is active and your weight is supported. So a single shared threshold heart rate for every sport produces skewed zones.
How do you find your LTHR?
A common field test is the same one used for threshold pace or FTP: a solo effort of about 30 minutes at race intensity, taking the average heart rate over the last 20 minutes as an estimate of your LTHR. Do the test per sport, well rested and under normal conditions.
Watch out for distortions: heat, dehydration, caffeine and lack of sleep push your heart rate up, and heart rate always reacts with a delay to changes in pace. So a single off reading is no reason to adjust your anchor straight away.
How Trimetra personalises this
Trimetra keeps a separate running LTHR and cycling LTHR and builds the matching zones per sport. The app recognises patterns in your own sessions — for example when your heart rate at a given pace consistently comes out differently than your anchor expects — and then makes a reasoned adjustment suggestion that you can accept or reject.
Frequently asked questions
What is the difference between LTHR and maximum heart rate?
Your maximum heart rate is the highest your heart can go; your LTHR is your heart rate around threshold — the effort you can just about sustain for a long time under control. Zones anchored on a measured LTHR are more reliable than zones from an age formula, which can easily be dozens of beats off for individuals.
Why is your threshold heart rate lower on the bike than when running?
Cycling uses less muscle mass and your weight is supported, so your heart works less hard at the same effort. One shared threshold heart rate for all sports therefore produces skewed zones — determine it per sport.
Can you determine your LTHR without a lab test?
Yes. A common field test is a solo effort of about 30 minutes at race intensity; the average heart rate of the final 20 minutes is your estimate. Do the test rested and under normal conditions — heat, caffeine and sleep deprivation push your heart rate up.
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