A way to measure the swimmer’s lactate levels is performing a lactate threshold set. If a swimmer starts off at a slower pace for 50s, lactate initially goes up for about 15 minutes or so, then decreases and is at a constant rate for a long time. If they are asked to swim at a faster pace, the lactate level spikes and then comes back down at a steady rate, but all at a higher level than before. Lastly, say the swimmer was asked to swim at an even faster pace than the first two times. The lactate shoots up high for the first few minutes, but then the swimmer starts to slow down and is unable to hold the pace anymore.

Looking at the diagram above, each line represents a specific intensity at which the swimmer completed the same distance, testing out which effort was at their lactate threshold. The red line depicts the athlete experiencing an exponential increase in lactate – the point at which the swimmer has reached their body’s threshold level of being able to clear lactate and metabolic waste product. Because the lactate levels did not come back down or level out from the initial spike, this swimmer found their threshold – the fastest pace speed they could maintain without the lactate levels skyrocketing.

Sprinters versus milers is a common comparison in lactate threshold. If a sprinter and a miler raced in a 100, the sprinter would win. This is because the race was not long enough for the lactate to build up and shut down the sprinter’s body. However, the sprinter’s lactate levels would be higher than a miler’s in a 100 race, because the sprinter is able to produce a lot of power from their glycolytic system, which results in a lot of lactate creation from the anaerobic emphasis. The miler is not able to produce a lot of power through the glycolytic system; thus, they struggle to produce high speed and a high level of lactate. The miler’s aerobic system is so efficient and programmed toward longer, less intense races, that it isn’t used to producing short bouts of speed and power.