The lactate test is a blood test that measures the level of lactic acid made in the body and the heart rate during a step test.
In this protocol power or pace is increased in regular steps, heart measurements and a lactate sample is taken towards the end of each step.
The amount of lactate in the blood is influenced by exercise intensity and lactate clearance.
Lactate is produced when carbohydrates are metabolized anaerobically (without oxygen) to produce energy, in a process called ‘glycolysis’.
As exercise intensity increases, a greater proportion of energy comes from carbohydrates, via the glycolytic energy system, leading to a higher lactate production rate.
Lactate begins to accumulate and to increase when lactate production exceeds lactate clearance rate.
In other words, at higher exercise intensity supply of oxygen to the working muscles cannot meet demand, and rates of lactate production begin to exceed the rate at which they can be cleared, leading to an exponential increase in the rates of lactate production.
On the other hand, at lower exercises intensity (below LT1 = steady z1/2) for example, we see low lactate measurements because there is enough oxygen supply to the working muscles. Energy production is largely met by fat oxidation and the contribution from the glycolytic system is marginal. Lactate levels are subsequently constant and do not increase because oxygen supply is sufficient to clear lactate at the same rate at which it is produced. This is the intensity in which you would usually do a long run or long endurance ride (fat max).
Lactate can be easily measured in the blood, using a small sample of blood (finger tip), and can provide us with a lot of information about the metabolic processes that are happening in the body (aerobic vs anaerobic energy system’s development).
So using lactate as a performance measure offers us a great deal of benefits over just power and heart rate data alone (e.g. MAP or FTP testing).
Measuring lactate can be a useful method to determine training zones. These training zones are connected to actual metabolic conditions within the body, and therefore have better physiological worth than zones based on maximum heart rate or FTP (functional threshold power testing).
It can be used to plot a lactate & heart rate curve, determine approximation of LT1, LT2, VLamax (glycolytic power = maximal lactate building rate) and ultimately your optimal training zones for your endurance training.
Furthermore, lactate concentrations depend upon an athlete’s unique physiology and fitness level.
Without going into too much detail here, however, your aerobic capacity aka V02max dictates the maximum oxygen supply to the working muscles, and thus LT2 (anaerobic threshold) which is the point at which lactate production starts to exceeds the body’s capacity to clear lactate. LT2 is a balance between V02max and VLaMax. LT2 increases if V02max increases relative to VLamax. Or, LT2 decrease if V02max decrease relative to VLaMax.
Given that lactate is a product of glycolysis, the higher the maximal glycolytic rate (VLamax) or a higher the tendency to produce energy via the anaerobic energy system (=a strong anaerobic development), lactate productions rates will typically be higher across the spectrum of intensities (meaning even at relatively low watts or running pace we are measuring higher lactate levels). So this would typically (not always) lead to lower LT1 and LT2 power in an individual with a higher VLaMax.
We can assess VLamax with a lactate testing protocol. This test can be used to identify the peak lactate concentration, and the lactate clearance rate. Beside the lactate step test that provides us with approximations of LT1 and LT2, we can also use a maximum lactate steady state test (MLSS) to determine LT2 power more accurately.