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 will 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 exceed’s 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, blood lactate analyzer, fingerstick blood collection supplies

Participant: one person from each lab section will be the participant. Other students are needed for these tasks: time master, RPE collector, HR collector, TM speed adjustor, and recorder

Instructions: One participant will walk/run on a treadmill until voluntary exhaustion. We will be using a discontinuous exercise protocol. There are many adjustments that can be used; please follow the instructions from your course instructors on what to do for this test.

During the test, the participant will be monitored with a HR monitor. There are other students who will assist with data collection. RPE should be collected at 30 seconds remaining in the stage, and HR with 15 seconds remaining. Your instructor will briefly stop the treadmill to collect a small blood sample to use in the blood lactate analyzer.

Please be sure you copy down the data from the test so that you can practice the graphs that you will need to do for the lab report.

This lab has an accompanying handout to help you collect data from the lab. It is provided as a Word document so you can use it either electronically or print it out to use.

Note: The figures and tables used in the lecture that corresponds to this lab are located in the folder for the lactate lab