What is lactate and lactate threshold?

Joe Beer explains all you need to know about lactate, lactate threshold, and how it affects your performance

The biggest adaptation a trained athlete can show is the capacity to use lactate as a fuel  © Triathlon.org/Delly Carr

Think of lactate as a high value currency of energy. It’s used as a way to shuttle high quantities of energy via the blood. Whether at rest or racing, ‘lactate’ circulates in your body, acting as a vital exchange of energy from birth until death.


At rest, there’s usually about 1 unit (i.e. 1 millimole) of lactate in the blood. This plasma lactate level can sometimes drop during very easy exercise, but slowly increases to 2 units once you hit 80% of maximum heart rate.

Plasma lactate is actually the net spillage of lactate made in the muscle, minus that recycled by the metabolism. We’re not often aware of the degree to which lactate fuels muscle contractions, but research has proven that the biggest adaptation a trained athlete can show is the capacity to use lactate as a fuel, both during and after training.

Lactate threshold

Lactate threshold is often talked about using terms which may be confusing, so I prefer to talk about 2 units as Zone 1 (74-84% of max HR) and above 4 units as Zone 3 (89-94% of max HR), to clearly show areas of low lactate and high lactate, respectively. Zone 2 (85-88% of max HR) includes the ‘anaerobic’ threshold (4 units) and is what I refer to as the lactate accommodation area.

But in terms of how lactate affects performance, I’ve broken this down into four bullet points:

  • Once above the threshold, you significantly increase the rate at which glycogen is used, and therefore reduce the time you can sustain such effort before glycogen starts to run short.
  • You have a limited time in the accumulation zone (Zone 3) where eventually the muscle starts to shut down due to ‘chemical fatigue’ processes, possibly before the first point above occurs.
  • Importantly, while the threshold area shows the tipping point of lactate dynamics, it appears the wrong place to focus too much training effort – you need to be below it (<2 units) or way above it (5 units+) to receive the best LIT and HIT training stimuli.
  • To be able to race short events or parts of longer events near to this threshold area, you need to practice. However, don’t be mistaken into thinking this is a quick-fix training solution for limited session time – you still need base training to be endurance fit.

Many effective athletes have never had their threshold or lactate levels up to and past this zone measured. They use heart rate, but understand how the internal lactate level determines how much stress is going on and how far their body can last. Therefore, remember that threshold is only a signpost to your fitness and performance, not the be-all and end-all.

Explained: why lactic acid is your friend, not foe

Two run drills to improve your tolerance to lactate build-up