Lactic threshold (LT) is the exercise intensity beyond which blood lactate begins rising exponentially. Below LT, you can sustain steady output for hours; above it, accumulation forces a slowdown within minutes.
Mechanism: At LT, the demand for ATP outpaces aerobic supply and glycolytic flux ramps up. Training raises the threshold by improving mitochondrial density, capillary supply, and lactate clearance.
Use case: Threshold work is the bread of any conditioning program. 20-40 min at LT pace, 2-3x/week. Push the curve up over months.
Caveats: Lab testing is gold standard; HR-based estimates are 5-10% off. Stay at threshold, don't try to crush above it every session.