What is Lactate Threshold
Filed under: Exercise Science
Lactate Threshold (LT) is the most important trainable physiological benchmark in endurance training and performance. By definition, LT is the point where your body produces more lactic acid than it can remove. In reality, a person's LT is the best predictor of performance. It is a true indicator of how hard they have trained and how capable they are of exercising close to their aerobic potential (VO2max). As exercise intensity increases, so does your lactic acid production. As lactic acid increases in the muscle, it eventually seeps into in to blood system and becomes blood lactate. Blood lactate concentration is measured in millimoles (mM) of lactate per liter of blood (mmol/L). The scientific standard for the onset of blood lactic acid (OBLA) is 4mmol/L. An increase in blood lactate causes an increase in the hydrogen (H+) ion concentration in the blood. This increased concentration in H+ causes an acidic environment reducing muscle contractions causing performance to slow and power output to fall eventually forcing the athlete to slow down. The special characteristic about LT is that it is trainable to a much larger degree than VO2max. In trained athletes, blood lactate levels occur at a higher % of their VO2max. Below is a breakdown of LT as a % of VO2max:
Untrained, sedentary individuals - 40-50%
Moderately trained individuals - 65-80%
Elite, endurance athletes - 85-95%
Proper training at or above LT will cause the body to get stronger and delay the onset of blood lactate accumulation. Longer intervals and/or paced rides (tempo), one or two times per week, are ideal for developing strength and increasing heart rate (HR) and power output at LT. Some of the important physiological adaptations of LT training are:
Increased aerobic metabolism.
Develop Type IIa Fast Twitch muscle fibers to more aerobic, oxidative Type I Slow Twitch muscle fibers.
Increase mitochondria density allows for better lactate resynthesis.
Increase capillary density improves oxygen delivery and lactate removal from the exercising muscles.
Maintaining low lactate levels will also conserve the glycogen reserves which will extend the duration of high-intensity aerobic exercise. It should be the goal of every endurance athlete to apply the correct training to increase their blood lactate threshold and increase performance at a greater % of their VO2max. If all things are equal and two riders have the same VO2max, but rider A has a higher LT than rider B, rider A will usually always win the race. Who will win the race if rider A has a VO2max of 70 ml/kg/min and a LT of 70% of VO2max and rider B has a lower VO2max of 60 ml/kg/min but a higher LT of 85% of VO2max? Rider A: 70 ml/kg/min X LT 70% = 49 ml/kg/min VO2max @ LT Rider B: 60 ml/kg/min X LT 85% = 51 ml/kg/min VO2max @ LT There are several methods to determine LT. In the laboratory, blood lactate levels can be measured by taking blood samples with a simple finger prick at the different intervals of a progressive exercise test. LT is determined when there is a significant spike in the blood lactate level (OBLA). There are also several field tests that can performed. One of the easiest is the 30 minute time trial, using the last 20 minute HR average and/or power output. LT is closely correlated with performance such as time trial ability. Since LT is very trainable, this is one factor that the athlete has control over in training. Once an athlete has established their aerobic base in training, attention should be shifted to developing a solid LT with proper interval and tempo training. Regardless of the event, a high LT will increase performance and make you more successful at racing or just having fun and dropping your friends on group rides.
Determining Training Zones
This protocol is a thirty minute time trial based on Joe Friel’s Triathlete’s Training Bible. It can be adapted for any sport and your own LT heart rate should be determined for each sport you intend to use for your endurance training.
Test protocol:
After a 15 minute warm-up, finish with a few quick 20 seconds bursts to get your heart rate in the correct training zone.
The 30 minute TT begins.
At 10 minutes into the test, hit the 'Lap' button on your heart rate monitor, to get the average heart rate over the final 20 minutes of the test.
The average for the final 20 minutes is your Lactate Threshold or LT.
You should finish knowing you gave it everything you had.
15 minutes easy cool down.
Now you can do some simple math to determine HR training zones, either relative to your LTHR, or as a percentage. These zones are not hard and fast. Some authors recommend taking an additional 3-5% off of these zones for a 30minute time trial. You can do a 60 minute time trial taking your average HR for the last 30 minutes to get a more accurate lactate threshold heart rate
Training Levels % LTHR Perceived Exertion (1-10)
Level 1 (Active Recovery) < 68% <2
Level 2 (Endurance) 69-83% 2-3
Level 3 (Tempo) 84-94% 3-4
Level 4 (Lactate Threshold) 95-105% 4-5
Level 5 (VO2Max) >106% 5-6
Level 6 (Anaerobic) N/A >7
Level 7 (Neuromuscular) N/A Maximal
Reference:
1.) Triathlete's Training Bible, Joe Friel; D3 Multisport, Mike Ricci.
2.) Power Training Levels, By Andrew Coggan, Ph.D.