Definition of Lactic Acid and Blood Lactate
Lactic acid is produced in the muscle.
As lactic acid diffuses out of the muscle it appears in the blood as lactate.
A by-product of metabolism, lactic acid is formed in several tissues including skeletal muscle, intestines, the liver and heart, and red blood cells. In active skeletal muscle lactic acid is continually produced at rest and during exercise. Once it is formed in muscle, lactic acid quickly dissociates, diffuses, and appears in the blood as lactate. During rest and low intensity exercise, blood lactate concentration remains at low levels approximately <1 mmol/L. At moderate intensities blood lactate levels will range nom 2-5 mmol/L. During high intensities, close to maximum, lactate levels will be 10-25 mmol/L. The concentration of lactate that appears in the blood is the sum of lactate production and removal. If production exceeds removal, lactate accumulates in the blood and the concentration increases, which occurs during high intensity exercise. If the removal rate exceeds production, lactate is said to be "cleared", thereby reducing the lactate concentration.
Identification of Lactate Threshold
During an incremental exercise test, lactate levels remain low and relatively constant until a point is reached when the concentration of lactate in the blood increases very rapidly. Lactate threshold (L T) is identified as that point at which a 1 mmol/L increase in blood lactate concentration above baseline values is followed by another 1 mmol/L increase. The point at which lactate threshold occurs will vary between athletes depending on many factors such as current fitness, years of training, altitude, muscle fiber type,
and nutritional status. Several terms have been used to describe this exponential increase in blood lactate such as "anaerobic threshold" and "onset of blood lactate accumulation". In Sports Physiology at the United States Olympic Committee, we feel strongly that the term "anaerobic threshold" is inaccurate and inappropriate. We use the term lactate threshold.
Determination of Lactate Threshold under Laboratory and Field Conditions
Lactate threshold can be determined nom tests performed in a sport physiology
laboratory or in the field the athlete's training environment. The laboratory
provides a setting in which the sport physiologist can control external
conditions such as weather (temperature, wind), and allows the use of testing
equipment to accurately control velocity, grade, and power during physiological
testing. We know nom the scientific literature that external conditions and
resolute changes in velocity and power can dramatically change the blood lactate
response and thus, the determination of LT. In order to determine LT, an athlete
may complete six to eight stages at progressively harder intensities. For each
type of athlete these tests would be performed on a sport-specific ergometer
such as: treadmill, bicycle ergometer, rowing ergometer, canoe/kayak ergometer,
in-line skating on a treadmill, or roller skiing on a treadmill. Typically,
oxygen uptake (VO2), ventilation (Ve), blood lactate,
heart rate, and rating of perceived exertion (RPE) are measured during these
submaximal and maximal laboratory tests.
The determination of LT from field based conditions can provide the coach and athlete with a valuable picture of the blood lactate response under training-like conditions. LT test protocol in the field will require the athlete to attain target paces, target heart rates, or percent of maximal intensity. A runner may complete six to eight 1000-meter runs on a 400-meter track at different target paces. A cyclist may complete six to eight 5-minute rides on a flat road course at different target heart rates or target power outputs. Blood lactate, heart rate, and rating of perceived exertion, and velocity are measured. Typically, this is how we plot and graph these data at the USOC Sports Physiology Laboratory. Selection of LT begins with identifying a 1 mmol/L increase in lactate above baseline values and drawing a line through those data points. A second line is drawn where a further 1 mmol/L increase in lactate occurs. LT is selected where those two lines intersect. The velocity, power, heart rate, and RPE corresponding to LT are then identified and used to establish training intensities and design training programs.
The Value of Lactate Threshold in Training and Performance
LT can accurately assess training status.
Blood lactate is a more sensitive index of training intensity than other methods.
The pace associated with LT has been found to be one of the best predictors of endurance performance. A high correlation exists between 10k and marathon performance and the velocity at LT as compared to other commonly used measures, such as maximal oxygen uptake, (VO2 max). Thus, lactate variables such as running pace at LT, power output at LT in cycling and rowing, and heart rate at LT in cross country skiing can provide a better assessment of training status than VO2max. In addition, lactate concentration provides an accurate picture of the metabolic demands that occur during training. Consequently, blood lactate concentration is a more sensitive indicator of a training stimulus being elicited than heart rate, velocity, or rating of perceived exertion. LT is normally expressed as a %VO2 max, HR, %HRmax, or pace related term.
The LT when expressed as a percentage of V02, is high in the endurance-trained athlete. In sedentary individuals, for example, the LT may be at approximately 50-60% of VO max, whereas in endurance-trained athletes it typically occurs at around 75-90% of VO max. This is advantageous for the endurance athlete, where one can work at a higher VO2 max, therefore a faster pace, without large increases in blood lactate levels.
Adaptations from LT Training:
Lower heart rate or faster pace at the same blood lactate level.
Lower blood lactate levels at the same exercise intensity.
A "rightward and downward shift" in LT.
Training at LT will increase the %VO max at LT. The lactate threshold is very responsive to training. Following training the workload will increase allowing the athlete to work at a higher intensity without accumulating lactate and the lactate-associated effects of fatigue. The resulting training adaptations will shift the blood lactate curve to the "right"; indicating the athlete can perform at a faster pace or lower heart rate at the same blood lactate value. The lactate curve may also shift "downward" indicating lower blood lactate concentrations at the same exercise intensity.
Note, it has been observed that your lactate threshold will occur at a slightly lower blood lactate concentration, heart rate, velocity, or power output than what can be maintained during a 10 kilometer running race or 40 km cycling time trial. Therefore, your L T intensity may represent a 'minimum' intensity for threshold training. The velocity at L T may approximate marathon race pace.
The specific adaptations that are desired from training at LT depends on the length of the event. For instance, an endurance athlete competing in events from 30 minutes to two hours will benefit from training at the LT. This athlete wants to keep blood lactate levels low to have the ability to "clear' lactate quickly once it accumulates in the blood. Contrast this with the 1500 meter runner who competes for less than four minutes and will want to train well above LT. Lactate tolerance training (95% of VO2 max) is important because it enables the athlete to sustain intense bouts of exercise and to tolerate the high blood lactate levels, which accompany such efforts. However, be aware that very high blood lactate concentrations, resulting from certain high intensity workouts, may have deleterious effects. The acidosis associated with high blood lactate levels can cause damage to the muscle cell wall, which may take 24 to 96 hours for recovery. Thus, allowing sufficient rest following a high intensity workout is important.
Training Zones and Training Programs Based on LT.
The determination of lactate threshold provides a foundation from which training intensities and training programs can be established. Endurance athletes such as middle and long distance runners, road and track cyclists, swimmers, and cross country skiers can benefit from LT based information. Optimum training can be accomplished by using heart rates, paces, or power outputs which correspond to various blood lactate levels. Appendix 1 is an example of five training zones based from this test. Training zones below L T are designated to promote recovery and endurance adaptations. Training at LT will raise lactate threshold. Zones above LT are selected to develop VO2 max and anaerobic capacity.
Coaches and athletes can use the LT -based information to plan year-round training programs. From this information, the volume and intensity of a training cycle can be designed to elicit desired training adaptations. For example, daily workouts are based on various blood lactate levels. This may be strategically broken down to percentages of various workouts throughout the weekly or monthly training cycle.
Appendix 1. TRAINING INTENSITIES: Lactate Threshold and Training Zones
Intensity: very low, 2-3 mmol/L below LT, 30-50 bpm below LT
Duration: 30-45 mins.
Objective: To promote recovery following high intensity intervals or glycogen-depleting over-distance workouts. Maintenance of cardiovascular adaptations and muscle-skeletal system.
Intensity: moderate, 1-2 mmol/L below LT, 10-30 bpm below LT
Duration: 30 mins 3 hours
Objective: Develop peripheral training adaptations: increase fat metabolism, increase number of aerobic enzymes, increase size and number of mitochondria, increase capillarization.
3 LACTATE THRESHOLD
Intensity: moderate, TEMPO just below LT, or at LT + 5 bpm.
Duration: TEMPO 20-60 mins. continuous or LT Intervals 5-15 mins. with equal or one half recovery.
Objective: Increase LT (%VO2max at LT) and maximal aerobic capacity.
4 VO2max INTERVALS
Intensity: high, 1-2 mmol/L above LT, HR associated with 95% VO2 max.
Duration: 3-5 min. intervals with equal amount of rest
Objective: Develop central training adaptations: Increase stroke volume, increase maximal aerobic capacity, and lactate tolerance (buffering capacity).
5 INTENSIVE REPETITIONS
Intensity: very high 2-6 mmol/L above LT.
Duration: SHORT 30-60 seconds with complete recovery. LONG 1-2 minutes with complete recovery.
Objective: Increase anaerobic capacity and buffering capacity.