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It is difficult to have a conversation with a cyclist nowadays without mention of “FTP”. There is a lot of (often conflicting) information out there about what FTP is, and indeed what FTP isn’t. Given how integrated FTP seems to be in training and racing for endurance cycling, in this blog we are going to try and provide very a short run-down on what FTP is, and what it isn’t. We are not intending to blast, or promote, FTP; just clear up some of the confusion and provide some context for those interacting with it.
FTP stands for “functional threshold power”. This term was first used to describe the maximum power sustainable for 60 min, which is thought to approximate what physiologists might call the “threshold”. This is the workload at which a break-point in our physiology develops; we can no longer achieve what is referred to as a metabolic steady-state. It is important to recognise that this assumption will already have an exercise physiologist’s alarm bells ringing…what is the significance of an hour? Why not 45 min, or 90? Won’t the sustainable duration at threshold vary between-athletes? Yes, it probably will. This undermines the first assumption of FTP.
Conceptual validity issues notwithstanding, a 60-min FTP test – or hour of power – is not fun. The brutal nature of the test led to proposal of a less-intimidating 20-min test, in which the athlete instead performs 20 min of all-out exercise and 95% of the average power achieved is accepted as FTP (1). This proposal – to instead take 95% of the 20-min value to approximate the 60-min value, was not actually based on research, and it is only recently that 60 and 20-min power have been compared scientifically (8). In fact, recent research suggests that in trained male cyclists, 90% of the 20-min value is a better estimate of 60-min power (8), and that most cyclists will only be able to sustain 95% of 20-min power for ~50 min (2)
Regardless, as it is so widespread, it is useful to assess the developing literature on the relationship between 20-min FTP tests and more-difficult-to-access outputs from the laboratory. The short summary of these studies is that the 20-min FTP test does not generally provide systematically higher or lower values than things like the maximal lactate steady-state (3, 5, 7), critical power (9), or lactate threshold (2, 6, 10), it does not have great ‘agreement’ with these values. This means that 95% of your maximal 20-min power, or FTP, could be quite a lot more or quite a lot less than better measures of the physiological threshold it attempts to approximate – with the direction of the difference probably related to the individual athletes physiological profile (i.e. how developed they are anaerobically and in terms of their tolerance or durability). It is therefore probably not possible to apply any kind of correction factor to an FTP value to find your threshold.
A specific problem we encounter when looking to use FTP to prescribe training is the percentage we should use for low-intensity sessions, and the risk of overtraining. Specific low-intensity sessions, designed to boost volume but evoke low levels of stress, ideally need to be below the first threshold – not the one FTP estimates, but an even lower threshold sometimes referred to as the aerobic threshold. The relationship between the aerobic threshold and FTP is again unlikely to be consistent between individuals; 65% of FTP may be nicely below aerobic threshold and therefore of truly low intensity in one athlete, but above it and therefore quite stressful in another. The risk you run here is applying too much stress during low-intensity sessions. Percentages of FTP as training zones may therefore provide a starting point when working with an athlete, but should not taken as gospel. If you’re using FTP to prescribe these sessions you need to be willing to make adjustments to the percentages you use on-the-fly.
However, the 20-min FTP test is very reliable; which means if you test the same athlete twice in the same conditions, they’ll get about the same result (4, 7). This is important and may show that coaches could consider using FTP tests – or, more simply, 20-min power tests – as serial performance assessments over time. This can be particularly useful when working with athletes who do not compete in races very often, although careful consideration to its relevance should be made when working with athletes who are training for an event much longer than 20 min, like an Ironman. It is very possible that you can do a lot of good, specific training and get much better at Ironman without seeing much of a nudge in your 20-min power.
So, what really is FTP? FTP is now commonly taken as 95% of the maximal average power output over 20 min, which is designed to approximate best-efforts over 60-min. FTP probably overestimates 60-min power, and does not appear to be anchored to any specific physiological marker, with the relationship between FTP and the “threshold” measured in the laboratory varying depending on the specific athlete’s profile. These issues question the use of FTP to derive training prescriptions, though it may be a good starting point when working with athletes who do not have access to gold-standard laboratory testing. FTP is however a reliable performance assessment that can probably be used by coaches looking to track an athlete’s performance – over 20 min – over time.
References
1. Allen H, Coggan AR. Training and racing with a power meter. Boulder, CO: Velopress, 2006.
2. Borszcz FK, Tramontin AF, Bossi AH, Carminatti LJ, Costa VP. Functional threshold power in cyclists: Validity of the concept and physiological responses. Int J Sports Med 39: 737–742, 2018.
3. Borszcz FK, Tramontin AF, Costa VP. Is the functional threshold power interchangeable with the maximal lactate steady state in trained cyclists? Int J Sports Physiol Perform 14: 1029–1035, 2019.
4. Borszcz FK, Tramontin AF, Costa VP. Reliability of the functional threshold power in competitive cyclists. Int. J. Sports Med. .
5. Inglis EC, Iannetta D, Pass L, Murias JM. Maximal lactate steady state versus the 20-minute functional threshold power test in well-trained individuals: “ Watts ” the big deal? Int J Sports Physiol Perform : 1–7, 2019.
6. Jeffries O, Simmons R, Patterson SD, Waldron M. Functional threshold power is not equivalent to lactate parameters in trained cyclists. J Strength Cond Res : 1, 2019.
7. Lillo-Bevia JR, Courel-Ibanez J, Cerezuela-Espejo V, Moran-Navarro R, Martinez-Cava A, Pallares JG. Is the functional threshold power a valid metric to estimate the maximal lactate steady state in cyclists? J. Strength Cond. Res. (2019). doi: doi: 10.1519/JSC.0000000000003403.
8. MacInnis MJ, Thomas ACQ, Phillips SM. The reliability of 4-minute and 20-minute time trials and their relationships to functional threshold power in trained cyclists. Int J Sports Physiol Perform 14: 38–45, 2019.
9. Morgan PT, Black MI, Bailey SJ, Jones AM, Vanhatalo A. Road cycle TT performance: Relationship to the power-duration model and association with FTP. J Sports Sci 37: 902–910, 2019.
10. Valenzuela PL, Morales JS, Foster C, Lucia A, De La Villa P. Is the functional threshold power a valid surrogate of the lactate threshold? Int J Sports Physiol Perform 13: 1293–1298, 2018.