 Defining Lactic Acid and Blood Lactate
Lactic acid is a by-product of metabolism and is formed in several tissues of the body including skeletal muscle, the intestines, liver and heart. It is continually produced at rest and during exercise. Once lactic acid diffuses out of the muscle it appears in the blood as lactate. The concentration of lactate that appears in the blood is reflective of the balance, of production and removal. At rest, blood lactate levels have been reported to range from less than1mmol/L in endurance athletes and up to 2.5mmol/L in sports that are highly anaerobic in nature. During high intensity exercise that is close to maximal, lactate levels have been reported to range between 7-25 mmol/L. The highest blood lactates for endurance athletes tend are approximately15mmol/L and as the event/sport becomes more anaerobic higher values up to 25mmol/L are seen. This is common in sports such as ice hockey, sprint events such as the 800 meters and power sports such as downhill skiing. The goal in testing blood lactate levels is to increase tolerance and improve clearance at a ratio that is respective to the nature of the sport.
Assessing Blood Lactate Levels
The protocol for assessing blood lactate levels should always be reflective of the event/sport duration. Thus if you are assessing lactate for a sport such as ice hockey which requires repeated sprinting on ice, testing should be done on ice following a repeat sprint skate test. If it is for a sport such as triathlon in which a steady state is held for the majority of training bouts, then lactate values need to be monitored in the steady state.
Below are various ways to utilize lactate monitoring for a variety of situations. When measuring lactate, it must be remembered that the rate of lactic acid production in the muscle is several minutes ahead of appearance in the blood. Timing the point at which a blood sample is taken will be emphasized for each sport.
Endurance Sports
Assessing blood lactate in endurance sports is most commonly done during an incremental exercise test to identify a relationship of blood lactate to pace, power output or stroke rate. In order to obtain accurate measures of blood lactate each stage of the test must be long enough to allow for a steady state to be obtained. Research has shown that this requires anywhere from a 5-7 minute stage duration.
Testing to identify workloads corresponding to blood lactate values of up to the 4mmol/L range should not last more than a total of 30-45minutes, allowing for 6-7 stages to be completed. Heart rate and RPE should be measured along with the blood lactate response so that a full perspective of the objective and subjective response to the work intensity can be determined.
Together this can then serve to help identify training zones and monitor the “lactate threshold” which has been shown to be highly correlated to endurance performance. A maximal lactate value is then traditionally obtained from a maximal incremental test to exhaustion or at the end of a race. Blood lactate removal is then monitored by measurements taken every 2 minutes for 10 minutes following the exercise bout. This should also improve with training. The following are training zones which can be developed from the blood lactate profile:
Adaptations desired from monitoring the blood lactate profile of an athlete are dependent on event duration and will determine how frequently the athlete trains in each zone. Almost all athletes are looking for lower heart rates or a faster pace at a given blood lactate level and an improvement in the workload achieved at the “lactate threshold”. For endurance athletes that compete in events of 30 minutes or greater, the greatest goal is to keep blood lactate levels low and to have the ability to “clear” lactate quickly once it accumulates in the blood.
In contrast for the 1500m runner who competes for 3:30-4:30 minutes, lactate tolerance training is important because it enables the athlete to sustain high intense bouts of exercise and tolerate high blood lactate levels. However, training the “lactate threshold” and factors associated with endurance will allow for improved lactate clearance and thus improved recovery from high intensity workouts that produce high lactate levels. It must be noted that Zones 1-3 will feel rather easy to this type of athlete but this is important as it is intended to be a “lighter” training day that allows time for recovery from previous high intensity workouts.
Team and Technical Sports
The intricacies of many team and technical sports present a challenge to assessing the energy demands of these sports. Sports such as tennis, soccer, ice and field hockey have been classified as anaerobic endurance events. The average blood lactate values reported during team or technical events is anywhere from 4-8 mmol/L with peak values occurring at 15-25mmol/L after sustained intensive bouts. Average values reflect time spent on the sideline and recovery time between points and plays; thus they are influenced by time for clearance to occur.
Research on sports of anaerobic endurance has suggested that tolerance to lactate and the rate of clearance along with fatigue rate to repeated sprint bouts is of most importance and correlates well to performance. In addition, tests must be sport specific to find a relationship to performance.
An example of a sport specific test is the Reed Repeat Sprint Skate test for ice hockey. Athletes perform six all out 55m sprints on ice with 30 seconds recovery between each. Blood lactates are monitored immediately after and then every 2 minutes for 10 minutes following the skate. Removal rate and fatigue index is calculated. This test closely mimics sport play and can allow information to be provided on areas of conditioning needed for the athlete (i.e. lactate tolerance or clearance).
For the coach this information along with recovery heart rate provides information on the amount of time needed off ice to recover from an intensive bout on the ice. The athlete’s progress is considered to be improved if the 55m sprints can be performed faster and/or with a lower fatigue index. Improved speed on ice is often associated with increased lactate tolerance and a reduced fatigue rate is associated with improved lactate removal. Approximated heart rate zones from the maximal heart rate obtained during testing and RPE can be used in creating on and off ice conditioning sessions to improve both of these areas. Research by Snyder and Foster have found the relationship of blood lactate, heart rate and RPE to be positive and overlap. RPE and heart rate values can be found in the above table.
Power and Speed Events
Events such as alpine skiing, BMX cycling, 800m run performance and 200m swimming are all examples of anaerobic power events that last two minutes or less and require an ability to tolerate high levels of blood lactate. Frequently, athletes in these events are also competing in additional events or are required to compete in rounds within the same day or the following day. Thus the ability to remove lactate is also critical to recovery for the next race. In addition, many of them require a technical proficiency to be performed under these circumstances.
Testing for these sports are specific to the event and need to evaluate the technical efficiency at critical velocities. The 3x300m short duration track test to assess anaerobic running efficiency in 400/800m runners is an example of such testing. Athletes perform three 300m intervals at 80%, 90% and 95-100% of their 300m personal best. Recovery intervals between the 1st and 2nd 300m are 10 and 20 minutes respectively. Blood lactates are taken at the following times:1) 2 and 5 minutes following the first 300m run, 2) 2,5 and 8 minutes after the second 300m run and 3) at 5, 8, and 12 minutes of the final run. Heart rate is also recorded. Peak blood lactates and heart rate for each repetition is graphed against velocity. The slope and shift of running velocity versus blood lactate curves across time will indicate whether or not the athlete has adapted to training. Athletes can improve performance by two means: 1) lactates will be lower at the same velocity indicating an improved clearance rate and 2) peak lactate and maximal speed is increased indicating an increased anaerobic capacity.
Traditional blood lactate profiles for identifying the lactate threshold and aerobic training zones are not commonly done in sprint athletes however, this doesn’t mean that measuring lactate is not a useful tool. Instead, it is recommended that blood lactates are further assessed in the field during these specific training sessions, along with heart rate and RPE, to ensure the athlete is not training too hard or outside of the blood lactates identified for those zones.
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