The lactate threshold gets so much attention in endurance sports that, despite its esoteric name, most athletes who have passed beyond the newbie stage are familiar with it. The term “lactate threshold” refers, of course, to the exercise intensity at which lactate, an intermediate product of aerobic metabolism, begins to accumulate in the bloodstream because the muscles are producing it faster than they can use it.
Simple enough. But when you drill down into the concept of the lactate threshold, things get messy. The first wrinkle is that there are numerous ways of defining the lactate threshold. Among them: the exercise intensity at which the blood lactate concentration reaches 4 mmol/L, the exercise intensity at which the blood lactate concentration begins to increase exponentially, and the exercise intensity at which the rate of blood lactate concentration’s rate of increase is greatest. No single definition of lactate threshold is inherently more valid than the others, and when they are applied to the results of a single lactate threshold test, they set the LT at slightly different levels.
A second wrinkle is that, even when you settle on a particular definition of lactate threshold, the specific testing protocol used to determine an individual athlete’s LT will affect the results. For example, an LT test with 4-minutes stages is likely to yield a slightly different result than an LT test with 2-minute stages.
A third wrinkle is that, because the lactate threshold is a metabolic event, it is affected by a variety of factors other than an individual athlete’s current fitness level, such as diet. If you do an LT test after a day of low-carbohydrate eating, you’ll get a different result than you will from an LT test done the day after high-carbohydrate eating.
Then there’s the question of the LT’s practical relevance. Contrary to pervasive beliefs in the endurance sports community, there is no sudden leap in the rate of fatigue when the lactate threshold exceeded. Athletes can sustain speeds/power outputs slightly above LT almost as long as they can sustain speed/power outputs slightly below LT. Nor is training precisely at LT uniquely beneficial. Training slightly above or slightly below this level produces pretty much the same results.
The ventilatory threshold is a different story. It is defined is the exercise intensity at which the breathing rate begins to increase at a faster rate than it does at lower intensities. The reason this happens is that the brain is required to begin to recruit large numbers of fast-twitch muscle fibers in order to meet the desired level of work output. This makes exercising even slightly above the VT is significantly more stressful to the nervous system than exercising even slightly below it. Consequently, training above the VT generates more fatigue and takes longer to recover from.
Research has consistently shown that endurance athletes at all levels gain the most fitness when they do about 80 percent of their training below the ventilatory threshold. Although supra-VT training is important and beneficial, athletes just can’t handle very much of it, whereas sub-VT training is so much gentler on the nervous system that athletes can handle a whole lot of it and must do a whole lot of it to realize its full benefits. The single most important thing you can do to keep your training on track is to know where your personal ventilatory threshold lies and is this knowledge to stay below it about 80 percent of the time.
Now, you might be wondering: If the ventilatory threshold is so much more reliable and important than the lactate threshold, why are our 80/20 training intensity zones based on lactate threshold? The short answer is “tradition.” The LT and the VT are measured in completely different ways. Direct measurement of the LT requires taking of small blood samples throughout an exercise test, whereas direct measurement of the VT is done through a method known as spiroergometry, which entails collecting and analyzing exhaled gases during exercise. It so happens that the LT was first identified in 1930 and the VT almost three decades later, in 1959. Having gotten a big head start, LT testing has remained the preferred method of quantifying moderate exercise intensity, despite its limitations. Hence, all of the commonly used field tests for establishing individual training intensity zones, including those that the 80/20 scale relies on, are designed to determine LT, not VT.
Because there is a mathematically consistent relationship between the two thresholds, however, LT tests can be used to determine VT as well, and this is precisely what the 80/20 zone scheme is set up to do. A new study conducted by Spanish researchers and published in Frontiers in Physiology found that, in a group of 22 trained male runners, the ventilatory threshold consistently fell slightly below the lactate threshold (actually the maximal lactate steady state, in this case) in terms speed, heart rate, and perceived effort, as shown in the table below (Note that MAS = Maximum Aerobic Speed, VT1 = Ventilatory Threshold, MLSS = Maximal Lactate Steady State, HRmax= Maximum Heart Rate, and VT2= Second Ventilatory Threshold, which is the exercise intensity at which hyperventilation occurs).
On the 80/20 intensity scale, the lactate threshold corresponds to the top end of Zone 3, which puts the ventilatory threshold in Zone X, which, in turn, ensures that when you train in Zones 1 and Zone 2—as you will do about 80 percent of the time when you follow one of our 80/20 training plans—you are at low intensity.
Having said all of this, I will also say I am hopeful that one day soon we will be able to develop a complementary alternative intensity scale that is anchored directly to ventilatory threshold testing. Currently I am trying out a wearable device that is capable of measuring the VT through accelerometer technology, specifically by measuring the rate and degree of lung expansion and contraction. Bending to tradition, though, the makers of this device are currently using the device’s VT estimates to determine LT. I’d like to talk them into providing users with their VT value instead, or additionally. Stay tuned.