Answers to some Frequently Asked Questions about Lactate Testing:

Just what is lactate?

Lactate is the form in which lactic acid is measured, but both terms can be used. The acid itself is produced in many of the cells of the body but particularly in muscle cells during exercise. From these cells lactic acid diffuses out into the blood where it can be measured. Accumulation occurs when the supply of oxygen to the cells is limited either because the muscle cells are working so hard that the supply cannot keep up or because the supply itself is deficient for some reason. During everyday activities, such as walking, the oxygen supply to the muscle cells is sufficient to enable the cells to utilize energy from various sources without recourse to the lactic acid route. However, when there is a sudden need for excessive muscular effort the lactic acid mechanism is available to enable activity to continue even though the oxygen supply is insufficient. This is known as the anaerobic phase of exercise in contrast to the aerobic phase which implies an adequate oxygen supply to the muscle cells. Generally, during exercise the blood lactate level is an index of the degree of anaerobic energy utilization.

You should be aware that this and what follows is a much simplified account of energy metabolism and that other metabolic pathways and mechanisms are involved. These, however, are relatively inaccessible to measurement in the usual sports training context.

What happens to lactate during exercise?

At rest the lactic acid mechanism is just `ticking over' so the blood level of lactate is low at about 0.5 1.6mmol/L (millimoles per litre of blood) but as the intensity of exercise increases so the blood level of lactate rises. It is possible to plot the lactate level against the exercise intensity and this forms a curve which steepens gradually at first but then suddenly becomes very steep as the intensity increases. Eventually exhaustion occurs at which time the lactate level might be 10 or 20 times the resting level. For most individuals the exercise level at which the curve becomes very steep is constant. It is referred to as the `lactate threshold' at a level of about 3.5-4.0mmol/L. If the curve is plotted during various phases of training it will be seen that it shifts to the right when there is improved performance implying higher intensity exercise at the same or lower lactate levels. On the other hand a shift to the left will occur if performance declines. When exercise stops the lactate level falls much more slowly than during the build-up. This is the process of recovery from exercise, sometimes referred to as the `warm-down'. Various factors influence the rate of recovery and knowledge of these factors can be useful in training. For example, moderate exercise during recovery accelerates the rate of lactate fall.

Can too much lactate be detrimental?

Yes. The acidity generated inside muscle cells when lactic acid builds up can be detrimental in two different ways depending on the time scale. During intense or prolonged exercise lactic acid build up is the reason that fatigue occurs. For some very short duration athletic events most energy is derived from the anaerobic (lactic acid) mechanism and training for such events aims to create tolerance to high lactate levels. The other way in which lactic acid can be damaging is in training for endurance events where most energy is derived from aerobic metabolism. In this situation above-threshold levels maintained during the greater part of training is believed to impair energy production and hence performance.

How does lactate information help with my training?

You can determine your own lactate curve and threshold for your chosen event by measuring lactate against incremental workloads. Once established, you can devise your training program so that the exact amount of work at, above and below your threshold is carried out. Therefore incorrect training levels will be eliminated and only quality work will be done. Too much training above or significantly below your personal threshold could be damaging or ineffective. In time you will learn the relationship between perceived effort and the lactate level, and from then on only occasional spot checks in relation to a defined exercise will suffice to maintain efficient training.

I already use a heart rate monitor so why should I measure lactate?

Because heart rate assesses only the rate at which the body's blood pump is working whereas lactate is a direct product of muscular work and rapidly diffuses into the bloodstream. Since the early 80's lactate has been regarded by most exercise physiologists as the most valid parameter that can be routinely measured when monitoring training status. Unlike the lactate v work-rate curve, the heart rate v work-rate curve shows no useful inflection for identifying the aerobic/anaerobic threshold and hence controlling training and following performance development.

In what sports can lactate monitoring be useful?

Virtually all endurance as well as the so-called `explosive' events, for example, swimming, rowing, cycling, athletics (sprint to marathon runners), speed skating and weight lifting. In team games too, such as soccer and ice hockey, lactate is used to assess fitness and monitor training. Any athlete from mid-teens upwards who takes his/her training seriously or coaches who want to provide the very best individual training program for their athletes to ensure they do the right amount of quality work, should consider lactate monitoring.