Lactic Threshold

Of the three energy systems (Alactic, Lactic, Aerobic) it is the lactic that can work against you as well as for you!

Throughout every run, we all use lactic energy to a greater or lesser extent. We cannot decide not to use it. The faster or more intense the run (for example sprinting 400m or running up a steep hill), the more likely we will use a greater proportion of lactic energy. The advantage of lactic energy is that it doesn’t require oxygen, meaning the energy is available quickly. The disadvantage is the waste product.

Thinking of running up a steep hill, your legs will fatigue and begin to feel heavy. What is happening is that lactate is produced in the muscles and used as fuel which then creates waste products. It is the build-up of the waste products that will slow you down.

When you walk or run slowly the rate of lactate production is low and your body can clear the waste products. As activity is increased, the amount of lactate produced increases and a point is reached where the body clears the waste products at the same rate as they are produced, known as the Lactic Threshold (LT). The LT is the pace at which we run when the amount of lactic production is the same as the rate of waste clearance. We are then getting maximum benefit from our lactic energy system.

Further increase in activity will lead to more lactate production, with the waste products being produced faster than the body can clear them. Heavy legs or even ‘hitting the wall’ is the consequence. Once the LT is exceeded, it is really difficult to get back under the LT without stopping.

The consequence is that when training, our objective is to better deal with the waste products from lactate energy so that the LT is increased and we can run faster or further before the LT is reached or exceeded  We can improve our LT pace in two ways, by a decrease in our lactic production and by an increased rate of waste clearance.

The best measure of a runners LT is by examining their blood, not something we can readily do! However LT is probably the best predictor of race pace for races of 8k to half marathon, for 5k and shoter races, VO2 max is more significant as the proportion of aerobic enegy used is lower.

When training to increase our LT, we need to know what is the continuous pace we can run at without tipping over the LT. The Lactic Threshold Pace.

For most of us we can use a low tech method to gauge our LT pace by considering race performances (not training performances).

  • For most experienced runners, LT pace is that you could race at for one hour without stopping.
  • For faster runners, LT pace is race pace for 15k
  • For elite runners, LT pace is somewhere between race pace for 15k to half marathon
  • For those who usually run shorter distances, LT pace is about 6 to 10 secs per km slower than 10k race pace or 12 to 18 secs slower per km than 5k race pace
  • Or using heart rates, LT pace is the heart rate when we are running at 15k race pace, or racing for one hour.

See Lactic Threshold (Tempo) Runs for a guide on how to train to increase your LT.

Graeme Loudain – September 2019

These notes are published as a general aid to all endurance runners. They are guidelines based on current best practice, intended to illustrate the points in the articles rather than provide a precise training schedule. They are written in a way to be of help to runners. Individuals will have their own requirements and the content of the notes will not suit all. Please use them in the spirit in which they are intended and modify them to suit your own needs. If you have suggestions for improvement, amendments or comment, please email