“Good job on improving your FTP!” my then coach Richard Laidlow congratulated me two years ago. My Functional Threshold Power was now 290 watts, he informed me, and I was thrilled. A year later came the cold shower: I did a physiological test with a different coach, and my Anaerobic Threshold was measured as 250 watts – how had I lost 40 watts, and where had they gone?
I subsequently learned more about the aerobic pathway, where energy is released from glucose and fat in the presence of oxygen. Using this aerobic energy system, I’m able to produce only 250 watts – the ‘missing’ 40 watts were from my body’s anaerobic contribution, where energy is unlocked from glucose without oxygen. FTP included both: the watts I was producing aerobically and anaerobically. The key lesson was that there are multiple thresholds, each meaning different things – so why as cyclists do we rely so heavily on FTP?
It’s important to remember that aerobic and anaerobic pathways are always intertwined and working together. Many of us assume that FTP tells us the pace we’re able to ride for an hour – but often this doesn’t stack up in practice. Setting aside discrepancies between different power meters and apps, how can we be accurate in how we discuss and apply FTP in our training? More importantly, is FTP the best metric to assess our fitness and upon which to base our training intensities — or should we look elsewhere?
What is FTP?
The scientific definition of FTP, according to the “father of FTP”, exercise physiologist Andy Coggan is “the highest power that a rider can maintain in a quasi-steady state without fatiguing for approximately one hour.”
Notice the qualifiers in there – a certain level of approximation is built in.
“When power exceeds FTP,” Coggan continues, “fatigue will occur much sooner, whereas a power just below FTP can be maintained considerably longer.”
The word ‘functional’ is the key to understanding the reliability and validity of FTP – it is functional because it has a practical and useful application in the power-based world of cycling. However, FTP values are neither absolute nor 100 percent precise. Moreover, the classic ‘20-minute power times 95 percent’ method of establishing FTP is not a definition, but only a protocol developed by coach Hunter Allen – with whom Coggan co-authored the book Training and Racing with a Power Meter in 2006.
In physiological terms, FTP is a practical estimation of your metabolic steady state; that is, it estimates the intensity you’re able to sustain for a long period of time. Exactly how long? More on that question below. For now, it’s important to note Coggan’s use of the words “quasi” and “approximately”.
“A true metabolic steady state doesn’t exist,” says the physiologist. “Even at low to moderate intensities, there are changes in oxygen uptake, fuel utilization, lactate, and hormone levels.”
The rate of these changes is quicker at higher intensities, and the transition from the quasi-steady-state – an effort level that feels hard but manageable – to a definitely not steady-state – being forced to ease off – can happen very quickly.
Exercise physiologists have, for decades, used the term lactate threshold (or just ‘threshold’) to describe this transition point. The lactate thresholds are the two points beyond which blood lactate accumulation occurs.
The Lactate Threshold 1 (LT1) is the point beyond which there is a sustained increase of blood lactate concentration, but a steady and tolerable one for the body. The Lactate Threshold 2 (LT2), on the other hand, is where the accumulation becomes rapid, meaning the effort is no longer sustainable. FTP attempts to identify LT2, but without measuring lactate levels in the blood.
Again, we must remember that physiological responses cannot be nailed down with pinpoint accuracy – thresholds are not black and white; the lines are always blurred. Historically, the Maximal Lactate Steady State (MLSS) has been considered the gold standard of metabolic steady-state – the highest effort level that can be sustained without continual blood lactate accumulation. The classic approach to test it requires several lab visits to quantify the lactate response to bouts of exercise lasting 30 to 40 minutes.
That’s why alternatives requiring single (or no) visits to labs emerged: Individual Anaerobic Threshold, which is based on lactate measurements, Lactate Minimum (a three-step test that estimates the balance between the appearance and clearance of arterial blood lactate), and their mathematical counterpart, Critical Power (CP), which is similar to FTP, but determines the maximum power sustainable over different durations, i.e. CP20 relates to 20 minutes, CP30 to 30 minutes, and so on. FTP, as Coggan describes it, was a “pedagogical construct” intended to solve the confusion around thresholds.
History of FTP
Coggan began reading up on exercise physiology when he was in high school. He grew up reading the scientific literature on the lactate threshold, which cemented his idea that threshold as a measure of muscular metabolic fitness was the most important metric to determine endurance performance. As a cyclist, he’s been training with power (on an ergometer) since the winter of 1977-78. As a grad student in the late Eighties, Coggan tested cyclists, including himself, and coauthored the study ‘Determinants of endurance in well-trained cyclists’.
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