Lower Threshold Power (LTP) is a value derived from your Fitness Signature representing the point your Threshold Power (TP) would fall to if your high-intensity and endurance energy reserves were fully depleted. It marks the approximate boundary between low-strain aerobic effort and effort that begins drawing on glycolytic energy reserves.
Definition
Lower Threshold Power (LTP; roughly analogous to LT1 or Aerobic Threshold/AeT) is derived directly from two components of your Fitness Signature: Threshold Power (TP) and High Intensity Energy (HIE).
In simple terms: LTP is the power you could still hold at TP-like effort even after your higher-energy reserves are exhausted.
What It Represents
LTP defines the approximate boundary between effort that relies primarily on aerobic, fat-based metabolism and effort that begins drawing meaningfully on glycolytic (carbohydrate) energy and starts contributing to longer-term fatigue
Below LTP:
- Effort is low-strain and highly repeatable
- Fat oxidation dominates, carbohydrate use is minimal
- Recovery demand is lower
At or above LTP:
- Glycogen use and lactate accumulation begin increasing
- Endurance Energy depletion accumulates, even at moderate perceived effort
How Xert Calculates LTP
LTP = TP − (HIE ÷ 400s)
Because LTP is calculated from your Fitness Signature, it updates automatically as your TP and HIE change — you don't need to test for it separately.
How LTP Relates to LT1 / AeT
LTP is analogous to LT1 (First Lactate Threshold) or the Aerobic Threshold (AeT), though it isn't derived the same way. LT1/AeT are measured directly from physiological data (blood lactate, gas exchange, etc.); LTP is calculated from your power data via your Fitness Signature. Both represent roughly the same underlying concept — the gradual shift from aerobic to glycolytic metabolism — but they are not guaranteed to match a lab-tested value exactly.
Where You'll See It
In your Profile Header, as part of your Fitness Signature.
In the Xert EBC app & data fields, as part of the "rainbow gauge" — LTP marks the transition point from blue to green
Common Misunderstandings
- LTP is not a physiologically-tested value like LT1 or AeT — it's a mathematical derivative of your Fitness Signature.
- LTP is not fixed — it moves whenever your TP or HIE change.
- LTP is not the same as riding "easy." Effort can feel moderate while still sitting above LTP and accumulating fatigue.
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