FTP is a performance estimate over time
Functional Threshold Power describes the highest power sustainable for about 60 minutes. Popularized by Andrew Coggan, it is commonly estimated from a 20-minute test or a ramp protocol. A factor such as 0.95 extrapolates a shorter effort rather than directly measuring blood lactate.
LT2 is a metabolic threshold
LT2 is estimated from lactate measurements across increasing workloads in a step test. The German article discusses concentrations around 3.0–4.5 mmol/L while stressing that individual values differ substantially.
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FTP is a time-based power estimate; a lactate threshold describes a metabolic transition. The source discusses differences of 10–20 watts for some athletes, typical differences of 0–15 watts at a good performance level and larger mismatches in beginners. FTP-derived zones can therefore sit above an athlete’s measured metabolic threshold.
Use the value that fits the decision
FTP is practical for power-meter interval sessions. Lactate-derived thresholds add context for metabolic training zones, long-event pacing and the interpretation of training changes. Knowing and periodically comparing both values is more useful than treating them as interchangeable.