Using Lactate Threshold Data

The following is an exclusive excerpt from the book NSCA's Guide to Tests and Assessments, published by Human Kinetics. All text and images provided by Human Kinetics.

Information provided by a lactate threshold test has a number of purposes. By understanding the role that lactate plays in exercise metabolism, the exercise physiologist can use the information from lactate threshold tests to predict proper racing and training paces, and assess the fitness of a subject or the efficacy of the training program. Although lactate production does not contribute to acidosis and lactate itself does not appear to cause fatigue, blood lactate accumulation does indicate that the body is relying on substantial contributions from anaerobic glycolysis to meet exercising energy requirements. Knowing the exercise intensity at which this occurs is valuable for two reasons: When glucose and glycogen are metabolized to lactate, only two or three ATP molecules are generated per molecule of carbohydrate consumed compared to the 36 to 39 ATP molecules that are generated when pyruvate is produced and consumed through oxidative phosphorylation. Thus, the advent of lactate threshold signals that the body is consuming glucose and glycogen at an increased rate in respect to ATP production, which, ultimately, can lead to premature carbohydrate depletion and exhaustion. Therefore, athletes who partake in events that challenge their glycogen storage capacity should take into consideration the need to preserve carbohydrate stores when planning their pacing strategies.

Increases in blood lactate concentrations also indicate that the subject’s ATP consumption rate is beginning to exceed the ability to provide ATP through the oxidative pathway. The increase in blood lactate levels seen at this transitional intensity indicates that the body has to rely on glycolysis to provide adequate ATP supplies for the exercising muscle. Though lactate production does not result in acidosis and has a questionable role in causing fatigue, the accumulation of lactate in the blood indicates that maximal sustainable rates of exercise and ATP production are close at hand (Morris and Shafer 2010).

The relationship between lactate threshold and the rate of consumption of carbohydrate stores, and correlations between lactate threshold and maximal sustainable work rate, make lactate threshold a good predictor of endurance exercise performance. Previous studies (Foxdal et al. 1994; Tanaka 1990) have demonstrated close agreements between running paces at lactate threshold and average paces during competitive running events in distances ranging from 10,000 meters to the marathon. In studies using cycling ergometry, power outputs that elicited lactate threshold were similar to average power outputs during time trials ranging from 60 to 90 minutes (Bentley et al. 2001; Bishop, Jenkins, and Mackinnon 1998). However, in time trials ranging from 25 to 35 minutes, subjects typically maintain significantly higher power outputs than those that elicited lactate threshold (Bentley et al. 2001; Kenefick et al. 2002). Despite these discrepancies, correlations between power outputs at lactate threshold and average power outputs during the shorter time trials remained remarkably high, suggesting that performance in these events can be predicted from lactate threshold data with reasonable accuracy.

As in many physiological and anatomical systems, the mechanisms that influence lactate threshold are responsive to exercise training. Properly designed training programs can increase the capacity of the oxidative pathway by increasing oxygen delivery to the working muscle (Schmidt et al. 1988), mitochondrial numbers (Holloszy and Coyle 1984), and oxidative enzyme levels (Henriksson and Reitman 1976). These improvements in oxidative capacity increase the muscle’s ability to produce ATP, consume pyruvate, and regenerate NAD resulting in a reduced reliance on lactate production and an increase in work rates that are required to elicit lactate threshold.

Unlike maximal oxygen consumption, which can be significantly influenced by genetic factors (Bouchard et al. 1986), the exhibition of lactate threshold when expressed as a percentage of maximal oxygen consumption is primarily influenced by the level of conditioning (Henritze et al. 1985). This sensitivity to exercise training makes lactate threshold useful for assessing aerobic fitness and the efficacy of training programs. Well-trained endurance athletes tend to exhibit lactate threshold when exercising at 80% or more of their maximal oxygen consumption, whereas untrained people experience lactate threshold at substantially lower intensities (Joyner and Coyle 2008). Continued training at or above the work rate that elicits lactate threshold also results in increases in the power outputs that cause increased rates of lactate production and accumulation (Henritze et al. 1985). Therefore, the efficacy of a training program can be assessed by measuring lactate threshold prior to, and following, program implementation. A rightward shift, as seen in figure 6.10, suggests that the training program has been successful in increasing the work rate that elicits lactate threshold and maximal sustainable work rates.

The ability of lactate threshold to respond to training and predict competitive performance also makes it useful in prescribing proper training intensities. Scientific evidence supports the overload principle of training (Weltman et al. 1992), which suggests that the most effective way to improve physiological capacity is to train at an intensity that exceeds current ability. Thus, effective training strategies involve assessing athletes’ current performance capacities and using work intervals that exceed their current maximal sustainable work rates. Undoubtedly, the most accurate way of measuring an athlete’s performance capacity in a particular event is to measure performance during that event. Unfortunately, lengthy endurance events such as the marathon are physically taxing, which makes performing them simply to test performance capacity impractical. However, the relatively short and low-stress nature of a lactate threshold test makes it ideal for frequently assessing an athlete’s ability.

PROFESSIONAL APPLICATIONS

Tim is a competitive distance runner who has recently set a goal of running his first marathon. He has a history of strong performances in 10K road races and wants to run a fast time in his first marathon. Tim recognizes the concept of progressive overload and knows that to improve his ability in the marathon, he must train at a pace that is faster than the speed he could maintain for the entire 26.2 miles. However, if he trains at a pace that is too fast, he won’t be able to do the volume of training that is required to perform well in his upcoming competition. He is very aware of his abilities at the 10K distance, but the marathon is roughly four times longer than the 10K, and he knows that he cannot maintain this pace for the entire marathon.

Tim visits an exercise physiologist, who is also a distance runner, for advice. The exercise physiologist agrees that Tim’s competitive pace for the 10K is far faster than what he could maintain for the entire marathon. The exercise physiologist is aware of research demonstrating that pace at lactate threshold is typically very similar to the pace that can be maintained for a marathon and suggests that Tim undergo a lactate threshold test.

The exercise physiologist chooses a step protocol because it will identify the running pace that elicits lactate threshold more accurately than a ramp protocol. Stages for the test will be three minutes long to stabilize blood lactate levels in response to each new workload. The pace of each stage will increase by one-half mile per hour to determine the pace that results in lactate threshold.

The starting pace must be one that will allow Tim to complete four or five stages before blood lactate levels begin to rise. This will establish a baseline from which to identify lactate threshold. Tim has recently competed in a 10K run, finishing in 36:00, which roughly translates into a six-minute mile, or a pace of about 10 miles per hour. Well-conditioned endurance runners can maintain a pace for a 10K race that is slightly faster than their pace at lactate threshold. Thus, 9.5 miles per hour is a good estimation for a pace that will elicit lactate threshold. To start the test at a speed that will put Tim at 9.5 miles per hour within four stages, the exercise physiologist multiplies the number of stages (four) by the rate of increase in speed for each stage (0.5 mph). The resulting figure of 2 miles per hour is then subtracted from the suspected lactate threshold speed of 9.5 miles per hour to give a starting speed of 7.5 miles per hour.

Prior to starting the test, Tim warms up for 12 minutes. The warm-up begins at a relatively slow speed of five miles per hour and remains here for the first two minutes of the warm-up. At the two-minute mark, the speed is increased by 0.5 miles per hour and is increased by this amount every two minutes for the remainder of the warm-up. This progression will have Tim running at the starting pace for the lactate threshold test (7.5 mph) for the final two minutes of the warm-up.

This approach accomplishes three things:

• It allows Tim’s body to adjust to the metabolic demands of the starting work rate of the lactate threshold test.
• It allows Tim to experience the starting speed for the test and reduce his apprehension going into the test.
• It gives Tim the chance to experience the pacing progressions for each stage of the lactate threshold test.

Once he has finished the warm-up, Tim steps off of the treadmill. He and the exercise physiologist have four to five minutes to make final preparations for the test. For Tim, this may include using the restroom, stretching, or double-knotting his shoelaces to make sure they do not come untied and interrupt the test once it has started. The exercise physiologist takes this time to double-check that all of the necessary equipment is at hand and properly calibrated.

To begin the test, the exercise physiologist starts the treadmill and sets the starting speed of 7.5 miles per hour. Tim then steps on the treadmill belt, and the exercise physiologist starts the stopwatch. After three minutes of running, Tim straddles the treadmill belt and the exercise physiologist uses a needle to make a small puncture in Tim’s finger. A small blood sample is taken from the wound and introduced immediately to the lactate analyzer. The exercise physiologist then places a small piece of gauze on Tim’s wound before the treadmill speed is increased by 0.5 miles per hour, and Tim returns to running on the treadmill. This procedure is repeated until an obvious and sustained increase in blood lactate levels is observed over the course of several stages.

Upon termination of the test, the exercise physiologist plots the lactate values against their respective running paces and sees an obvious inflection point at a speed of 9.5 miles per hour. This pace is likely the highest average pace that Tim could maintain for a marathon. Because his objective is to improve his ability before the competition, Tim should use 9.5 miles per hour as a minimum pace for his long training runs, and paces in excess of 10 miles per hour for interval workouts.

With proper training, Tim’s lactate threshold will increase, which will increase his minimum training pace. Measureable improvements can be expected within about four to six weeks, necessitating a subsequent retest of Tim’s lactate threshold. These regular reassessments will be useful in assessing the efficacy of the training program and in reestablishing proper training paces as Tim’s ability improves.

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