The Relationship Between Lactate and Acidosis
Along with VO2 max, aerobic threshold and running economy, your lactate threshold is a key determinant in your running performance. In fact, it's probably an even more important a factor than VO2 max.
Lactate threshold is often also referred to as anaerobic threshold. Simply defined it is the point at which the buildup of lactate exceeds your body's ability to clear it from its cells. Lactate is a byproduct of your energy production systems.
As you begin to run harder or go for longer, your body builds up lactate as well as acidity. Often the term lactic acid is used. However this isn't necessarily correct. Many runners mistakenly assume that lactate is responsible for making them tired or causing muscle damage. By itself, lactate is harmless. You could inject lactate into your bloodstream without any major effect. In fact, your heart and other muscles can use lactate as fuel.
However, the acid part of lactic acid does have profound effects on running. The acidosis caused by long or intense running is what depletes your energy and causes your muscles to get tired and sore. We can only measure acidosis indirectly. As your lactate levels increase so does the amount of acidosis in your system. Since the acidosis can't be measured directly in a convenient and timely manner, sport scientists use a test which measures blood lactate levels. Over time, the term "lactic acid" has been incorrectly used to describe the concurrent buildup of lactate and acidosis.
What Your Lactate Threshold Tells You
By measuring the amount of lactic acid in your system at different speeds you can correlate heart rate and the amount of lactate in your system. As you approach your maximum your lactate levels (and the accompanying acidosis) increase exponentially until you are forced to stop.
I recently had some physiological testing done at the Peak Centre in Vancouver and here are the results showing my lactate curve.
You can see the hockey shaped lactate curve, which is a good response. As the exercise intensity increased so did my lactate levels, acidosis and heart rate. At lactate threshold (4 mmol/l) my speed was 13.2 kph (kilometres per hour) and heart rate was 180 bpm (beats per minute). In terms of pace, this was equal to 7:19 min/mile but this was on a treadmill. Converting to an outdoor pace, this is equal to 6:48 min/mile.
This is my lactate threshold pace and heart rate. Below this pace and heart rate I can clear lactic acid from my system and delay fatigue. Above it, lactate and acidosis accumulate quicker than I can clear it and I fatigue quicker until I have to stop.
Testing Lactate Threshold
Runners can use a number of different tests to determine their lactate threshold.
A lab test is done on a treadmill and involves getting your finger tip pricked at specific intervals to draw a blood sample. This blood sample is then measured to determine how much lactate has accumulated. The analyzers in most labs are very high quality. The level of lactate is expressed in millimoles per litre of blood volume. Lactate threshold can be provided in terms of heart rate, percentage of V02 max, running pace or speed.
There are also portable analyzers which can measure lactate levels out in the field. This involves taking a blood sample at specific intervals which the analyzer then measures for lactate concentration. The quality of the results can vary depending on the skill of the tester and the accuracy of the analyzer. Some machines are very accurate while others are questionable.
Field tests can also be done to estimate your lactate threshold pace and heart rate. Many running coaches use 10K race performance to provide a good estimate of a runner's lactate threshold.
In labs, the lactate threshold test can be done at the same time as a VO2 max test and gives accurate results. But the cost and inconvenience are factors to consider. Field tests are cheaper and easier to do but the results may be very inaccurate.
Training Lactate Threshold
Threshold training is not as intense as VO2 max training but it still involves a hard effort. Interval training is a great method to train your lactate threshold. The intervals are relatively long, between 5 - 10 minutes and the recovery periods are as long as the interval (5 - 10 minutes).
For runners with high fitness levels, threshold runs between 20 and 40 minutes of continuous effort can also be done. But remember you will be working at a hard effort, up to 90% of your maximum heart rate so these continuous effort runs should only be done by experienced, fit runners. For others, the long interval method is a better way to train lactate threshold.
Improvements are seen by being able to run faster at your lactate threshold and/or increasing your heart rate at this level. Generally speaking, the limit that you can increase your lactate threshold is 95% of your maximum pace and/or heart rate.
Lactate Threshold and VO2 Max
To give you an idea of what effort you need to run different races, here's a good chart from the team at the Peak Centre.
SPD = speed while the annotions Z1, Z2, etc. designate heart rate training zones (i.e. Zone 1, Zone 2, etc.) So your marathon race pace is at or just above your aerobic threshold while your 10K race pace is at your lactate threshold.