Tricky Threshold Terminology
You will hear a lot of people talk about 'threshold' when it comes to their training, but which one are they talking about? What does this really mean? Does it matter if they are running at VT2, LT2, or Anaerobic threshold? We try to give some answers here!
There are two key thresholds/breakpoints which we can measure. First and foremost there are several definitions and ways of measuring what we prefer to call the anaerobic threshold, and fewer ways of measuring what we define as the aerobic threshold.
Anaerobic threshold definitions
FTP (functional threshold power). Is probably the most common of these terms and is generally regarded as the best quassi steady state power an individual can hold for a one hour time trial. More recent definitions and programs such as WKO4 have attached a different time period, known as time to exhaustion, to this metric due to the fact that some people appear to be able to hold the power considered their ‘threshold’ for well over an hour, or others far less than an hour. This relies on sophisticated modelling algorithms and accurate power data over multiple time periods to calculate the time to exhaustion at the given power output.
MLSS (maximal lactate steady state). Is the power at which a rider can reach a blood lactate concentration of around 4mmol/L (it can vary a little between individuals) and would stay at this level for around 1 hour if this intensity was maintained. Recent evidence has shown really a maximal lactate steady state only really exists if the individual builds up to this power output and then maintains it. It is perfectly possible to make a hard effort for several minutes, reach a blood lactate concentration of 12mmol, or perhaps more, and then settle into threshold power and maintain blood lactate as this high level.
VT2 (ventilatory threshold 2). The second breakpoint in respiratory rate. The breathing rate increases significantly beyond this point, becomes more rapid, and often less controlled. It is difficult to maintain a conversation at this intensity, let alone string together more than a few words.
OBLA (Onset blood lactate accumulation). The point at which blood lactate begins to accumulate at an (almost) exponential rate for harder work rates. Essentially the same as our next definition, the anaerobic threshold.
Anaerobic threshold. Is the power at which lactate production and lactate combustion are equal. This is our preferred definition of ‘threshold power’. While it is possible to reach short term secondary lactate thresholds above anaerobic threshold due to negative feedback loops on lactate production, any significant time spent above anaerobic threshold will result in continued blood lactate accumulation. It is important to note you do not ‘go anaerobic’ above this point, it is still highly aerobic, and often well below VO2max, but above this level the by-product of anaerobic glycolysis, lactate, cannot combusted by aerobic metabolism as fast as it is being produced by anaerobic metabolism
LT2 (Lactate threshold 2). Generally the same as anaerobic threshold. The second break-point on the lactate curve
Aerobic threshold definitions
What is this lesser known aerobic threshold? Many people get caught up in what their FTP/anaerobic threshold number is, but may not even know about the aerobic threshold which is of just as much importance and is impossible to measure with heartrate or a power meter alone, metabolic data is a must.
VT1 (ventilatory threshold 1). Where respiratory rate sees the first major increase above baseline if measuring using a metabolic cart. In general this is the level at which conversation becomes switches from easy to a little difficult due to the increase in breathing rate.
LT1 (Lactate threshold 1). The intensity at which lactate begins to rise above baseline (generally around a 1mmol increase is considered sufficient)
Now we have these thresholds defined, stick around for future posts where we will discuss why they are important to training, some misconceptions around FTP and training based off it, why MAP step tests without metabolic data don’t fare much better than a basic FTP estimate, why lactate testing is the gold standard for aerobic and anaerobic threshold measurement, for setting training zones, and also for deciding what the physiological target of future training should be.