Lactate Threshold

Lactate Threshold: what is it?

Lactate is not a waste product and it does not cause the burn. It is a fuel that muscle, heart and brain use continuously, and blood lactate concentration simply reflects the balance between how fast it is produced and how fast it is cleared. At low intensities that balance holds and the concentration stays near resting values. Push harder and production overtakes clearance, the curve bends upward, and the intensity at which that happens is what coaches call the lactate threshold. It is the best single predictor of endurance performance, because it defines the fastest pace a client can hold without a countdown timer running.

Two thresholds, not one

Most testing models describe two breakpoints on the lactate curve rather than one. The first is where lactate first rises meaningfully above baseline. The second is the highest intensity at which production and clearance still balance - the maximal lactate steady state. Different traditions name them differently, which is the main reason threshold discussions get confusing.

The practical distinction is duration. Around the first threshold, a fit client can go for hours. Around the second, they can hold on for something on the order of 30 to 60 minutes before the effort collapses. Anything above it has a short and predictable ceiling.

How it is measured and how it is approximated

The reference test is a stepped protocol with a finger- or earlobe-prick blood sample at the end of each stage. Plot lactate against intensity and read the breakpoints off the curve. Fixed concentrations such as 2 mmol/L and 4 mmol/L are often used as shortcuts, but individual curves vary enough that a fixed value can misplace a given athlete's real threshold by a meaningful margin.

Without a lactate meter there are three usable proxies. A 30-minute all-out time trial gives an average pace or power close to the second threshold. The talk test locates the first threshold well: full sentences are comfortable below it and become clipped above it. Heart rate works too, but only as a percentage of the client's own threshold heart rate, never as a percentage of an age-predicted maximum.

• Test in the mode the client trains in - running threshold and cycling threshold are different numbers.
• Control the variables: same time of day, similar carbohydrate intake, no hard session the day before.
• Express results as pace, power or heart rate so they can be used in a session, not as a concentration.
• Retest every 8 to 12 weeks; threshold shifts faster than VO2max in trained athletes.

Training the threshold

Threshold moves through two levers. Increasing clearance capacity - more mitochondria, more lactate transporters, better perfusion - is driven overwhelmingly by volume at low intensity. Increasing the intensity at which the balance breaks is driven by controlled work at or slightly under the second threshold: sustained tempo efforts, or cruise intervals of 8 to 15 minutes with short recoveries.

The classic mistake is spending every session in the middle. Work that sits just above the first threshold and just below the second is tiring enough to compromise the next hard session but not specific enough to move either end. Keeping easy work genuinely easy is what makes threshold sessions productive.

What to tell the client

Clients hear "lactic acid" and think of the burn and of soreness the next day. Neither is caused by lactate. Delayed soreness comes from mechanical damage to muscle fibres, and the burning sensation during hard work is driven by a broader set of metabolites and by hydrogen-ion accumulation.

The useful message is about pacing. Once a client understands that there is a line above which the clock starts, they stop starting every run too fast, and they stop treating every session as a test.