Glossary: Critical Power/Critical Pace/FTP
The following explanations always refer to "power" as the quantity to be considered, i.e. to CP = "Critical Power" and FTP = "Functional Threshold Power". However, the concept can also be applied to "Pace" (i.e. "Critical Pace" and "Functional Threshold Pace") or to "Heart Rate" (then CHR and FTHR).
What is FTP? FTP is originally defined as "the highest power that an athlete can maintain in a quasi-steady state for approximately one hour without fatiguing", although the actual duration for which an athlete can hold FTP can vary from 30 to 75 minutes. FTP is a measure of metabolic fitness and is used in both cycling and running.
What is CP? While FTP is a single value, CP usually describes a concept first: namely the hyperbolic relationship between power output and the time that the power output can be sustained. CP itself is the power asymptote of the relationship and can, theoretically, be sustained without fatigue; in fact, exhaustion occurs after about 30 to 60 minutes of exercise at CP. This makes CP actually something different from FTP, but it can be used interchangeably in certain cases.
How to calculate/estimate CP/FTP? There are many different methods to calculate or estimate CP or FTP. These are usually based either on an explicit test protocol (ramp test, 3/9-minute test, 2x8-minute test, ...) or on the performance curve (also "power duration curve"), i.e. the maximum average powers over different durations. In Runalyze, we primarily use the latter.
- CP ≈ CP60: The value of the power duration curve at 60 minutes.
- CP ≈ 95% * CP20: 95% of the 20 minutes value is used as an estimate for the 60 minutes value.
- Mathematical model: CP(t) = CP + W'/t (Monod/Scherrer)
In all methods it is important to use values of maximum effort. Individual values such as CP60/CP20 should therefore only be used if full exertion is available for 60/20 minutes in the period considered. However, even a model with several variable parameters can be significantly off the mark if the data are poor.
CP and FTP can be used as a measure of fitness, to define training zones, and to predict maximum power output (for up to 60 minutes). The CP concept provides another helpful value with W' (as "capacity").
See also
References
- Palladino, S.: Running Functional Threshold Power - A Primer, 2017
- Hill, D.W.: The Critical Power Concept. Sports Medicine 16, 237–254 (1993)., doi: 10.2165/00007256-199316040-00003
- Skiba, P.F., Chidnok, W., Vanhatalo, A., Jones, A.M.: Modeling the expenditure and reconstitution of work capacity above critical power. Med Sci Sports Exerc. 2012 Aug; 44(8):1526-32., doi: 10.1249/MSS.0b013e3182517a80
- Clarke, D.C., Skiba, P.F.: Rationale and resources for teaching the mathematical modeling of athletic training and performance. Adv Physiol Educ. 2013 Jun;37(2):134-52, doi: 10.1152/advan.00078.2011
