Background

Lactate testing

Our bodies are always using a variety of metabolic processes. This means that lactate is always being produced in a healthy human body. If we measured everyone in the class while they were seated at rest, everyone would

have a detectable blood lactate concentration. During exercise, the proportion of which system is being predominantly used shifts. As exercise begins and exercise intensity increases, when the aerobic (oxygen) demands of exercise can no longer be met lactate will increase in circulation (the blood).

Blood lactate is a better predictor than VO₂max for exercise performance. It is also more accurate to prescribe exercise intensity based on relative lactate threshold (LT) or maximal lactate steady state (MLSS) than heart rate. However, due to limitations in using lactate measures to prescribe exercise intensity (chiefly, the impractical aspects of lactate threshold testing everyone) heart rate is used to prescribe intensity for the average person exercising for health or to improve fitness.

The two blood lactate concentrations most frequently used to determine exercise performance are exercise intensity at LT and lactate produced at a specific intensity (for running protocols, usually 17km/hr). An individual who is “better-trained” will have a higher treadmill speed for their LT, and a lower blood lactate concentration at the specific intensity. These two measures can also be periodically re-tested to test performance improvement.

Therefore, it is useful to measure blood lactate and use the measures to determine exercise intensity for the exercise training plan. The values most frequently used to determine  exercise training intensity are lactate threshold (LT) and maximal lactate steady state (MLSS). LT is the point at which the body can no longer counter the rise in lactate, and there is a noticeable increase in blood lactate concentration. The body is not able to keep the amount of lactate low because of increasing exercise demands (an increase in anabolic metabolism) and the amount of lactate produced exceeds the body’s buffering capacity. This results in a shift from a linear increase in blood lactate concentration to non-linear. There is a significant increase of blood lactate appearance in the blood. MLSS is the exercise intensity that corresponds to the highest exercise intensity achieved without an increase in blood lactate (i.e. the intensity at LT).

Another term that is frequently used is onset of blood lactate accumulation (OBLA). This value corresponds to 4.0mmol/L. Sometimes this is referred to as the second lactate threshold. Since it is an absolute number and does not require plotting lactate concentrations to find the change from a linear to non-linear rise in blood lactate concentration, some people prefer to use this value to determine exercise performance improvements.

Class activity

Blood lactate concentration testing (lactate threshold test)

Equipment: Treadmill (or cycle ergometer), blood lactate analyzer, fingerstick blood collection supplies

Participant: One person is the participant. During a test, the test administrators monitor the time duration, participant’s RPE, participant’s HR, adjust the treadmill/cycle ergometer speed, and record all measures during the test.

Instructions: One participant will walk/run on a treadmill (or bike on a cycle ergometer) until voluntary exhaustion. A discontinuous exercise protocol is commonly used for this test. Similar to the VO2max test, there will be multiple stages of 2-3 minutes with each stage increasing in intensity until the subject reaches exhaustion.

During the test, the participant will be monitored with a HR monitor. RPE should be collected at 30 seconds remaining in the stage, and HR with 15 seconds remaining. A a small blood sample to use in the blood lactate analyzer will be collected at the end of each stage.

Note: The figures and tables used in the lecture that corresponds to this lab are located in the blackboard folder for the lactate lab. There is also an accompanying handout of what the data collection sheet during this test would look like if we were collecting data in person.

Video #1: Full lactate threshold test example

• This example uses a cycle ergometer. Tests can also be run on a treadmill, and our lab data is from a treadmill test. Both tests will use a discontinuous exercise protocol.

Video #2: How to calculate HR training zones with lactate

• This video is optional, but may help if you would like another example of calculating HR training zones.

https://www.youtube.com/watch?v=Tmw4veCeEfw&feature=youtu.be