Exercise Physiology 552 (1997) Brief Review:

The Influence of Exercising at the Lactate Threshold on the Aerobic Training Response

by Tracey Wheeler

 

Contents

Background Knowledge

  • The processes of aerobic and anaerobic metabolism.
  • The order of muscle recruitment during incremental exercise.
  • Adaptations of skeletal muscle to aerobic training.
  • The determinants of maximum oxygen consumption (VO2max)
  • The processes of production & removal of lactic acid from exercising muscles.
  • Recording blood lactate concentration.

 

Learning Objectives

  • Compare Lactate Threshold (LT) and VO2max as indicators of endurance performance.
  • Recognise other blood lactate measures used in predicting performance and prescribing exercise.
  • Understand the importance of training intensity and specificity in affecting performance gains.
  • Observe the relative improvements of LT and VO2max in response to training.

 

Introduction

At rest and during low level exercise, blood lactic acid levels are fairly stable.  Recent research indicates that lactate production is continuous and related linearly to work output.  As long as the removal rate can keep up with production, no significant lactate shows up.  At a certain point in exercise, production outstrips removal and the blood lactate rises dramatically.  This point is referred to as the Lactate Threshold (LT).  Reasons for the lactate threshold are:
  • As exercise intensity increases, more white, Fast-twitch muscle fibres are recruited.  Theses fibres are lower in oxidative capacity, but good at supplying energy anaerobically, producing lactate in the process. The more of these fibres that are recruited, the more lactate is produced.
  • Higher workloads increase sympathetic output, which tends to trigger glycolytic pathway activity (Fisher and Jensen 1990).

 

Lactate Threshold

Some inconsistency exists when defining the Lactate Threshold, and how it seems to be interchanged with anaerobic threshold (AT) and onset of blood lactate accumulation (OBLA) by many authors.  OBLA is possibly the best defined of the measures of blood lactate concentration(BLC) and is based on an exponential increase in BLC during incremental aerobic exercise (Astrand and Rodahl 1987).  Caution should be observed when assigning set levels of BLC (eg. 4mM) to threshold points (eg. OBLA, LT).  Maximum steady-state BLC has been found to vary between 2mM and 8mM (Hollmann et. al. 1986 in Weltman 1995), and therefore 4mM will be an appropriate threshold point for only some individuals.
 
The variation in defining a value to LT in some research (eg. 1mM, 4mM) is a source of possible problems in interpretting results, when LT has been used to measure training intensity.

The LT occurs at a different intensity for different people (Fisher and Jensen 1990). For untrained indivduals the LT may be as low as 40-50% VO2max.  For moderately trained 50-80% VO2max, and for highly trained it may be 90% + VO2max. Seip et. al. (1991 in McArdle, Katch and Katch 1996) found that an RPE (Borg Scale) of 11 corresponds to exercise at the LT for both trained and untrained subjects.
 

Lactate Threshold as a Predictor of Endurance Performance

There is a large volume of research suggesting that the blood lactate response to exercise is a better indicator of endurance performance than VO2max (Weltman 1995). It is believed that the blood lactate response to exercise and VO2max are determined by different factors, with VO2max being dependent on cardiovascular factors (ie. cardiac output and stroke volume) and the blood lactate response to exercise being dependent on peripheral factors, such as muscle fibre type and mitochondrial volume (Weltman et. al. 1992 in Weltman 1995).
 
Farrell et. al. (1979 in Weltman 1995) looked at the relationship between LT and VO2max in experienced runners, and their performance over a variety of distances.  For all distances LT was more strongly related to running performance than was VO2max.  The race pace associated with marathon running was very close to the velocity associated with LT, suggesting that if LT could be elevated as a result of training, marathon times should improve.
 
Other investigators have suggested that OBLA (4mM) is the best predictor of endurance performance.  Sjodin and Jacobs (1981 in Weltman 1995) found that marathon velocity occurred at about 87% of OBLA velocity.
 
Coyle et. al.(1988 in Weltman 1995) identified LT (1mM above baseline) of competitive cyclists with similar VO2max.  The lactate thresholds varied between 66% and 81.5% of VO2max.
 
Weltman et. al.’s (1987, 1989a,1990a in Weltman 1995) data suggest that any of the measures of blood lactate can be used in a research setting with similar accuracy.
 

Training Intensity

Of the variables that affect the aerobic training response (ie. frequency, duration, intensity), intensity is the most important in determining the degree of improvement and maintainence of gains.  If intensity is held constant, the frequency and duration of exercise required to maintain a certain level of aerobic fitness is much less than that required for its improvement (McArdle, Katch and Katch 1996).

Monitoring Intensity:  There are many methods of expressing training intensity.  For example:

  • Calories per unit time.
  • Power output, or velocity.
  • Percent of VO2max (%VO2max)
  • Below, at, or above LT, or a given lactate concentration.
  • Percent heart rate max.(%HRmax)
  • Multiples of resting metabolic rate (METs)
  • Rating of perceived exertion (RPE).

The most commonly used methods are %HRmax, or %VO2max.  For the general population the minimum intensity to produce an aerobic training response is exercising at:
70% HR max (approximately equal to 55% VO2max), or
60% of the difference between resting and maximum HR (60% of the heart rate reserve), or
a conversational level (ie. the intensity at which a conversation can just be held).

For the highly trained athlete aiming to improve aerobic performance, a more specific and individualised form of exercise prescription is appropriate.
 

Training at the Lactate Threshold

Several studies have reported that workload and oxygen uptake (VO2) associated with various blood lactate parameters improves to a much greater degree with training than does VO2max (Weltman 1995).

Denis et. al. (1982 in Weltman 1995) had their subjects training for 40 weeks at LT (80-85% VO2max.), three times per week.  The VO2 at LT increased by 11% while VO2max did not change.  It was suggested that changes in LT were related to local changes such as muscular oxidative activity rather than to cardiovascular adaptations.  These results would imply that athletes can improve their running times, by performing at a higher sub-maximal VO2 without needing to increase their VO2max.

Yoshida et.al. (1982 in Weltman 1995) had similar results with previously untrained subjects training at a BLC of 4mM, for 8 weeks on cycle ergometers.  Their lactate thresholds increased by 37%, compared to a 14% increase in VO2max.  These authors concluded that training at the intensity that corresponds to a 4mM BLC may be one of the most effective methods for endurance training.

Tanaka et. al. (1983,1986 in Weltman 1995) examined the relationship between improvemants in LT, VO2max and endurance performance in competitive runners.  Training resulted in increases in VO2max, LT and distance running performance, but only the change in LT was strongly related to changes in running performance.

These studies provide further evidence that the blood lactate response to exercise and VO2max are affected by differing mechanisms, and therefore VO2max should not be the sole measure for determining training adaptations.  Although intensity of training appears to be important, little is known about the minimal or optimal training intensity for improving LT, OBLA or other blood lactate responses to exercise.

Henritze et.al. (1985 in Weltman 1995) examined the effects of training at LT, and above LT, on changes in LT and VO2max.  College aged women who trained at the LT did not improve LT or VO2max.  Those that trained above the LT improved LT by 47% (when expressed as VO2 at LT).

To date there is no data available with regard to how soon the training adaptation in the blood lactate response to exercise occurs, or what the optimal training intensity is for altering the blood lactate response to exercise (Weltman 1995).
 

Specificity of Training

The specificity of training has been well documented for improving VO2max, but little information exists regarding specific training and changes in the blood lactate response to exercise.  As LT is thought to be affected by local muscular changes, specific types of training should have a greater impact on LT than on VO2max.

Pierce et. al. (1990 in Weltman 1995) tested the change in VO2 at LT on treadmill running, on males after training on either the cycle ergometer or running.  The running group improved LT by 58%, but the cycling group did not improve their treadmill LT.  These results have clear implications for designing training programs to improve fitness and endurance performance.
 

Summary

The blood lactate response to training adapts to a greater degree than VO2max.  This training  adaptation is specific to the mode of training.  Changes in VO2max. should not be the sole measure of training adaptation.  It appears that training to improve the blood lactate response to exercise is the type of training required to improve endurance performance.  Some evidence exists to suggest that training above the LT is beneficial, but  the optimal training intensity for altering the blood lactate response to exercise is still not known.  Periodic re-testing of the blood lactate - exercise intensity relationship is required to continually upgrade the level of training as improvement occurs.
 

Clinical Implications

The information presented here, in relation to improving LT in the absense of VO2max. improvements, highlights the capacity of adaptations of the muscle fibres.  This further emphasises the concept of specificity of training, even in tasks that have a high cardiovascular component.

Also highlighted is the lack of sensitivity of VO2max. in detecting significant improvements in endurance performance.  We need to be aware of this when interpretting VO2max. tests results, or field tests which VO2max. is extrapolated from.

 

Short Answer Review Questions

1. Define lactate threshold.

2.  How does VO2 at Lactate Threshold compare to the race pace VO2 of endurance runners?

3.  What physiological adaptations would cause an increase in VO2 at Lactate Threshold, without altering VO2max.?

4.  Would you expect these changes to significantly effect performance in endurance athletes? Explain.

5.  Is Lactate Threshold or VO2max. a better predictor of endurance performance?

6.  How would an athlete exercising at a given blood lactate concentration monitor their exercise intensity?
 
 

References

Astrand P and Rodahl K (1987): Textbook of Work Physiology (3rd ed.). Singapore: McGraw Hill, pp328-330.

Fisher AG and Jensen CR (1990): Scientific Basis of Athletic Conditioning (3rd ed.). Philadelphia: Lea and Febiger, pp 135,168.

McArdle WD, Katch FI and Katch VL (1996): Exercise Physiology: Energy, Nutrition and Performance (4th ed.). Philadelphia: Lea and Febiger, pp401-415.

Weltman A (1995): The Blood Lactate Response to Exercise. Current Issues in Exercise Science. Monograph Number Four. Champaign: Human Kinetics, pp49-97.