Lactate Threshold: What it is and why it’s Important
Lactate Threshold: What it is and why it’s Important
Lactate threshold can be utilized as a powerful training tool by both recreational and elite athletes. Scientifically, this threshold is defined as the work rate and which lactate is being produced faster than the body can metabolize it and therefore starts to accumulate. When the intensity of the exercise is decreased below the lactate threshold, your body is able to use the lactate for energy by the muscle, heart and liver. When exercise intensity is low enough, most of the lactate in the blood can be eliminated. However, if exercise intensity stays above lactate threshold athletes will get the burning sensation and subsequent fatigue that is associated with fatigue. If lactate concentrations become too high, the body can make your muscles stop working as a protection mechanism. The ability of the body to process lactic acid is highly trainable and is one of the major points of interest when training for sports with an endurance component. With the interest high in training this component, several direct and indirect methods of measurement of the lactic threshold have emerged. All of these methods have their merits and drawbacks and have served a purpose at some point even though several are now outdated.
When measuring intensity of exercise, ideally runners use pace and cyclists use power. With running, one variable that changes which can make pace difficult to use is the terrain on which the athlete is running. The composition of the ground as well as inclines and declines can cause a change in pace versus exercise intensity relationship. It also requires for an individual to know the distances between points on the course. However, it is the most direct measure of exercise intensity that can be used when training. Speed is very inaccurate for defining exercise intensity for cyclists due to the effect of external variables, even on the same course ridden on different days. Wind, tire pressure, road surface and many other variables make pace inconsistent at a given exercise intensity. Heart rate is also used to monitor exercise intensity. However, this is not ideal as heart rate can easily be influenced from levels of anxiety, meals, temperature, and hydration along with other variables. For cycling, power is the absolute measure of work being completed by the individual and is not affected by external variables.
An inexpensive and applied method of determining lactate threshold is by looking at an individual’s time trial or racing times. Depending on the race length, it may be necessary to apply the race times to different formulas. This compensates for the increase or decreased intensity due to the length of the event. This method of prediction has several assumptions involved that can make it an invalid measure. Primarily, it assumes that an individual maintains a constant pace throughout the effort. An intermittent hard effort during the race or time trial would make an individual alter their pace in order to recover. Often, athletes start out at a harder pace than what they finish which also effects the results. This also assumes that the individual competes at an effort that is high enough to provide results that can translate into lactate threshold. Different athletes can spend different amounts of time working at or above lactate threshold. An athlete may be able to perform above or below the assumptions made by this method. However, this method is inexpensive and relatively simple. It requires a minimum amount of equipment and is often utilized as a form of “field testing.” Individuals can set up a course with known distances to mark their pace with running and execute their own field tests. Cycling requires another form of measuring exercise intensity due to the high influence of external factors on pace.
Lab protocols serve to eliminate variables that affect lactate threshold and provide the most reliable results depending on the protocol utilized. However these results require the use of specific equipment and trained personnel. The lab must have a reliable and calibrated treadmill in order to ensure proper measurement of pace. For cycling, an ergometer is used to control the work rate for cyclists. Source Endurance uses a state of the art Woodway treadmill along with an SRM electronically braked ergometer to ensure accurate pace and power measurements. The protocol used in the testing also affects the reliability of the results. Athletes need to reach a point of steady state in respect to both lactate accumulation and oxygen consumption. This is the point that the fluctuations in various biological processes are minimized after responding to changes in exercise intensity. This can take several minutes. In a typical lactate threshold test, the intensity is increased a set amount at consistent increments. The difficulty in establishing these tests is making sure the test is long enough to provide accurate information but short enough for the athlete not become fatigued. A balance between stage length, number of stages, and the increase in intensity has to be established for a reliable test. Source Endurance implements a protocol for testing that ensures a steady state is reached and utilizes work rates customized for each athlete for the most accurate results.
One method utilized to determine lactate threshold that can be applied in both lab and outdoors settings is watching an individual’s respiration rate. As an individual’s exercise intensity increases, their breathing rate increases in order to provide more oxygen to the working muscle. However, respiration rate dramatically increases once lactate starts to accumulate in the blood. This is due to the body’s effort to buffer acid component of lactic acid. As the body buffers lactic acid, a byproduct is carbon dioxide. Carbon dioxide levels increase and drive the body to automatically increase breathing rate in order to lower the levels in the blood. However, this measure is an indirect measure of lactate levels and is subject to error. It can be difficult to measure the change in ventilation by sheer observation and can be somewhat subjective depending on the individual administering the test. Additionally, the athlete may alter breathing rate for a number of reasons. If performed in a non-laboratory setting, the test administrator needs to be able to monitor the respiration rate of the individual and therefore needs to run or ride with the athlete. Additionally, the testing environment needs to have known distance increments for runners or provide terrain for constant work rates for cyclists.
Often a VO2max test is paired with a lactate threshold test which requires the use of a metabolic cart in order to measure the composition and volume of inspired and expired air. If the lab incorporates the two tests into one (i.e. the use of a VO2 max test to determine LT), the results will be compromised and the stages of work will be too short to allow a steady state for the lactate threshold test or exercise duration will cause fatigue before VO2max is reached. If testing for both LT and VO2 max the tests should be performed with separate protocols and adequate recovery between each test should be given. Some lab protocols utilize the Respiratory Exchange Ratio (RER) when using a metabolic cart in order to define lactate threshold. This is the ratio of carbon dioxide exhaled to oxygen used by the body. An RER of 1.0 is used by these labs to define lactate threshold. This, however, is an indirect measurement and is subject to error. RER can be influenced by a range of variables from the fitness level of the individual to the most recent meal the athlete has eaten. Source Endurance performs both LT and VO2 max testing within the same session, however separate protocols and ample recovery between tests is given to ensure accurate and reproducible results.
The most direct measure of lactate levels is through measuring the levels of lactate in the blood. This concentration is expressed as millimols (mmol). This method requires trained personnel along with the handling of blood. The protocol has evolved over time in order to provide the most accurate results. For an example, in the past an arbitrary breakpoint would be established as lactate threshold such as 4.0 millimols. However, individuals have different levels of lactate circulating at different levels of exercise intensity from rest to the actual threshold. The current protocol supported by scientific research is a 1millimolar increase in blood lactate in two consecutive stages after a baseline blood lactate has been established. Source Endurance utilizes this method with the most advanced lactate tools for measuring lactate as well as maintaining a clean and safe environment while ensuring that the power, pace or heart rate data is accurate and specific to your own unique physiology.