Decoupling tests

Definition

“Decoupling tests” are workload tests in which a clearly defined, constant power or pace is held for a predefined time while the change in heart rate is observed. What is measured is the ratio of power to heart rate in the first versus the second half of the session. If heart rate rises at equal power, the two quantities “decouple”; the percentage difference is the test result, the aerobic decoupling.

Why it matters

A stable power-to-heart-rate ratio over one to three hours shows that the aerobic base holds. The body supplies energy at constant intensity without increasing cardiovascular strain.

Marked decoupling, on the other hand, points to insufficient base endurance, dehydration, heat, depleted glycogen stores or exhaustion. The method is therefore particularly suited to checking zone 2 training and long sessions.

These thresholds come from coaching practice, not from diagnostics. obseed uses the test as a progress check between two lab tests, not as a replacement for them.

How obseed measures it

obseed calculates decoupling from every recorded session that contains power or pace and heart rate. The session is split into two halves of equal length; for each half the Efficiency Factor is formed from normalized power and average heart rate.

Decoupling [%] = (EF_1st half − EF_2nd half) / EF_1st half × 100

For the value to be meaningful, the load should be constant and heart rate recorded with a chest strap. Optical wrist sensors produce outliers especially on long sessions, which obseed smooths but cannot fully correct. As a pointer to external confounders you note heat, altitude or nutrition manually on the session.

Example

An athlete rides 2 hours at a constant 200 W in his endurance zone.

1st hour:  NP 200 W, HR 138 bpm  →  EF = 200 / 138 = 1.45
2nd hour:  NP 200 W, HR 147 bpm  →  EF = 200 / 147 = 1.36
Decoupling: (1.45 − 1.36) / 1.45 × 100 = 6.2 %

The result sits just above the 5 percent mark. The base is present but not yet secured for two hours at 200 W. If he repeats the test after six weeks of base training and the second hour comes in at 141 bpm, decoupling drops to 2.1 %.