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You can think of Critical Power can be thought of as a threshold between aerobic and anerobic anaerobic exercise. While that's an oversimplification, it reflects the subjective feelings of the athlete quite well. In some ways it's similar to the idea of like [[Lactate Threshold]], but far easier to determine. The idea of Critical Power has been around since 1965<ref name="MonodScherrer1965"/>, but the rise of power -based cycling trainers, cycling power meters, and now the ability to estimate running power with [[Stryd]], the concept has gained new traction. Critical Power is the highest workload that you can be sustained sustain without using the anerobic your anaerobic reserve , and is research papers often considered the consider this workload that an athlete can be sustained sustain "indefinitely." In practiceOr course, "indefinitely" here means until glycogen reserves start to get depleted, or other limiting factors set in. Typically, so typically you can maintain Critical Power for 30-60 minutes can be maintained at Critical Power<ref name="Hill1993"/>. Above the Critical Power, there's an amount of work that you can be performed perform anaerobically. This anaerobic work capacity is typically called named W' (W-prime), and it . You can either be used use your W' at high intensity for a short period or a lower intensity for a longer period. This creates a curve of how long you can sustain a given high intensity power level can be sustainedabove Critical Power.[[File:CPModel_sience.png|center|thumb|400px|Critical power, from [https://www.goldencheetah.org/Golden Cheetah].]]=An Analogy for Critical Power=Here's a financial analogy for Critical Power. You could think of Critical Power as your regular income, and W' as your savings. You can spend your regular income almost indefinitely and not run out of money. If you spend your money faster than you earn it, you use up your savings. You could spend your savings slowly for a longer period, or quickly for a short period. Once your savings are gone, you must spend less than your income to build your savings back up. =Why should you careShould You Care?=I There are several benefits to knowing your Critical Power as a runner. * Improvements in your Critical Power show improvements in your fitness. This is a good way of evaluating the effectiveness of your training. * Critical Power can help define your running paces. To do this, you'll need to find your Running Critical Power (see the greatest benefit from below.)* You can use Critical Power for [[High Intensity Interval Training| HIIT]]on a bike trainer. A You can structure a HIIT workout can be structured based on your CP and W', using those metrics . You can use these values to understand how stressful (and how practical) a given workout will be. I use Golden Cheetah which will show the W' balance as a curve for a given workout. * The CP and W' can be used for pacing allow you to pace shorter races (30-60 minutes) as an . An ideal pace will be one in which you deplete W' is depleted evenly over the race, reaching near zero at the end. For longer races, other factors beyond W' depletion become the limiting factors, so it's less valuable there. HoweverAgain, CP can be used as a metric you'll need to evaluate for running potential (see belowknow your Running Critical Power.)
=Finding Your Critical Power=
The gold standard for measuring CP is to perform multiple tests to define points in the CP/W' curve. Each You need to perform each test needs to be performed while well recovered, so each needs to be on a separate day. After a warmup, you do a fixed power workout is performed that should result in cause your exhaustion between 3 and 15 minutes (durations less than 3 minutes may give an overestimate of CP<ref name="BishopJenkins2007"/>.) A total of five tests should be performed. Given these results, there are a number of several online calculators that will give CP and W' numbers, though I'd recommend https://shiny.fmattioni.me/CPapp/ which has multiple models, including the 3-parameter model if you have 4 or 5 test results. (As an aside, one One study found that CP occurred at around 83% of [[Maximum Heart Rate| Max HR]] <ref name="MielkeHoush2011"/>).
==The 3AOT Approach==
There's a simpler "3 minute all out test" (3AOT) that can estimate your CP. This is an test must be "un-paced" test where the athlete goes you go all out for the duration of the test. This means that power output will be very high for the first few seconds, then drop off as you deplete your W' is depleted. The idea is that by the end of the 3 minutesBetween 90 and 120 seconds, you should have depleted all of the your W' will be depleted and you can only the maintain your CP can be maintained. The limitation of the test is that any pacing by the athlete, even subconsciously , will overestimate CP and underestimate W'<ref name="Mandell2019"/>. There are several studies that have found the 3AOT gives a good estimate of CP/W'<ref name="BurnleyDoust2006"/><ref name="DekerleVanhatalo2008"/><ref name="VanhataloDoust2007"/>, and they . These studies found that it a 3AOT can detect relatively small changes in CP with from training (, such as increasing CP from 230-to 255w)<ref name="VanhataloDoust2008"/>. One validation technique that was a study used was to exercise at 15w above and then 15w below the critical power estimate. The study found the that athletes could not maintain 15w above could not be maintained past their CP for over 10-15 minminutes, where 15w below is their CP was stable from ~10 min up to 30 minminutes. However, one study found the 3AOT did not provide valid results in elite cyclists<ref name="BartramThewlis2017"/>, with . That study found that the 3AOT estimating estimated an average of 351w compared with 402w with multiple tests. This study found that the underestimated the athletes' W' was underestimated, with measuring an average of 15.5 kJ rather than 24.3 Kj.=Problems with Critical Power=There are three problems with Critical Power: the simplifications of the model, the reality of an anaerobic threshold, and repeatability. Let's look at each in turn. ==All Models Are Wrong==The quote "all models are wrong, but some models are useful" is appropriate here. There have been several extensions of the simple two parameter model<ref name="Morton2005"/>. These extensions add more accuracy at the cost of complexity. Morton's 1996 proposal for a "3-parameter" model improves the estimates of CP and W'<ref name="Hugh Morton1996"/>. There are online calculators that will use the more sophisticated models to give better estimates.==Anerobic Threshold==The idea of Critical Power, like [[Lactate Threshold]] is to find the cut off between aerobic and aerobic plus anaerobic energy production. In reality, there is no fixed line between the two. The definition of Critical Power is often in terms of the power output that can be kept up "indefinitely" <ref name="BishopJenkins2007"/>. But it's easy to see that pace or power output declines with increasing time in a curve with no sudden line that demarks an anerobic threshold. This means that the definition of an anerobic threshold tends to depend on how long "indefinitely" is. It seems that in the areas of anerobic thresholds, it's typically 20-30 minutes. There's some evidence that Critical Power corresponds to a 30+ minute endurance<ref name="HoushHoush1989"/>. ==Repeatability of Critical Power==A study of how training changes CP/W' performed a repeatability test<ref name="GaesserWilson2008"/>. Twice they performed five bouts with exhaustion times between 1 and 10 minutes. Each bout was on a separate day in random order, and the five bouts were repeated a week later. They found that CP had good repeatability, with a correlation of the two tests of 0.92. The repeatability of W' was lower at 0.62. This suggests that tests using this approach to determine CP are valid, but caution should be used with measurements of W'. =Finding Running Critical Power=Most work on averageCritical Power uses a stationary bike. I found one study that used multiple runs to exhaustion<ref name="HughsonOrok2008"/>. The study used 6 treadmill runs to failure in 2-12 minutes, each one separated by at least 48 hours. The treadmill used a safety harness, which reflects the problem with treadmill running to failure. It might be possible to do similar fixed pace outdoor runs using a vehicle for pacing. Unfortunately, that's not something many of us have access to. Another approach would be to self-pace using Stryd for accurate feedback but without a heads-up display, it would be tricky to maintain a steady enough pace for the results to be valid. Performing a 3AOT while running outdoors should be possible, but the all-out sprint at the beginning has high injury risk. [[Stryd]] will estimate your Critical Power, as described at [https://blog.stryd.com/2019/07/09/introducing-auto-calculated-critical-power/], but I've not seen any independent validation.
=Critical Power and Running Performance=
A study looked at the relationship between Critical Power and Running Performance<ref name="KolbeDennis2008"/> over 40m, 1km, 10km, and 21.1km (half marathon distance.) The study found a reasonable correlation between CP and both running performance and [[VO2max|V̇O<sub>2</sub>max]] for distances of 1km and longer. They found that CP corelated correlated with 75-85% of both values (r=0.75-0.85). =Critical Power and Power at V̇O2max=I find it interesting that Critical Power is halfway between [[Lactate Threshold]] and the maximum power attained during an incremental [[VO2max|V̇O<sub>2</sub>max]] test<ref name="PooleBurnley2016"/>. This suggests that the power achieved at [[VO2max|V̇O<sub>2</sub>max]] is partly from anaerobic sources. =Critical Power and Functional Threshold Power=A common power threshold in cycling is "Functional Threshold Power" or FTP. I recommend reading http://www.georgeron.com/2020/04/functional-threshold-power-FTP-myths-facts.html for a good analysis of the (lack of) scientific support for FTP.
=References=
<references>
<ref name="HughsonOrok2008">R. Hughson, C. Orok, L. Staudt, A High Velocity Treadmill Running Test to Assess Endurance Running Potential*, International Journal of Sports Medicine, volume 05, issue 01, 2008, pages 23–25, ISSN [http://www.worldcat.org/issn/0172-4622 0172-4622], doi [http://dx.doi.org/10.1055/s-2008-1025875 10.1055/s-2008-1025875]</ref>
<ref name="PooleBurnley2016">David C. Poole, Mark Burnley, Anni Vanhatalo, Harry B. Rossiter, Andrew M. Jones, Critical Power, Medicine & Science in Sports & Exercise, volume 48, issue 11, 2016, pages 2320–2334, ISSN [http://www.worldcat.org/issn/0195-9131 0195-9131], doi [http://dx.doi.org/10.1249/MSS.0000000000000939 10.1249/MSS.0000000000000939]</ref>
<ref name="KolbeDennis2008">Tracy Kolbe, Steven C. Dennis, Elizabeth Selley, Timothy D. Noakes, Michael I. Lambert, The relationship between critical power and running performance, Journal of Sports Sciences, volume 13, issue 3, 2008, pages 265–269, ISSN [http://www.worldcat.org/issn/0264-0414 0264-0414], doi [http://dx.doi.org/10.1080/02640419508732236 10.1080/02640419508732236]</ref>
<ref name="MonodScherrer1965">H. Monod, J. Scherrer, THE WORK CAPACITY OF A SYNERGIC MUSCULAR GROUP, Ergonomics, volume 8, issue 3, 1965, pages 329–338, ISSN [http://www.worldcat.org/issn/0014-0139 0014-0139], doi [http://dx.doi.org/10.1080/00140136508930810 10.1080/00140136508930810]</ref>
<ref name="MielkeHoush2011">Michelle Mielke, Terry J Housh, C Russell Hendrix, Jorge Zuniga, Clayton L Camic, Richard J Schmidt, Glen O Johnson, A Test for Determining Critical Heart Rate Using the Critical Power Model, Journal of Strength and Conditioning Research, volume 25, issue 2, 2011, pages 504–510, ISSN [http://www.worldcat.org/issn/1064-8011 1064-8011], doi [http://dx.doi.org/10.1519/JSC.0b013e3181b62c43 10.1519/JSC.0b013e3181b62c43]</ref>
<ref name="BishopJenkins2007">D. Bishop, D. Jenkins, A. Howard, The Critical Power Function is Dependent on the Duration of the Predictive Exercise Tests Chosen, International Journal of Sports Medicine, volume 19, issue 02, 2007, pages 125–129, ISSN [http://www.worldcat.org/issn/0172-4622 0172-4622], doi [http://dx.doi.org/10.1055/s-2007-971894 10.1055/s-2007-971894]</ref>
<ref name="Mandell2019"> Mandell, Paul K., "Effects of a race timer on the three minute all-out test for critical power" (2019). Theses and projects. 261. https://digitalcommons.humboldt.edu/etd/261</ref>
<ref name="Morton2005">R. Hugh Morton, The critical power and related whole-body bioenergetic models, European Journal of Applied Physiology, volume 96, issue 4, 2005, pages 339–354, ISSN [http://www.worldcat.org/issn/1439-6319 1439-6319], doi [http://dx.doi.org/10.1007/s00421-005-0088-2 10.1007/s00421-005-0088-2]</ref>
<ref name="Hugh Morton1996">R. Hugh Morton, A 3-parameter critical power model, Ergonomics, volume 39, issue 4, 1996, pages 611–619, ISSN [http://www.worldcat.org/issn/0014-0139 0014-0139], doi [http://dx.doi.org/10.1080/00140139608964484 10.1080/00140139608964484]</ref>
<ref name="BishopJenkins2007">D. Bishop, D. Jenkins, A. Howard, The Critical Power Function is Dependent on the Duration of the Predictive Exercise Tests Chosen, International Journal of Sports Medicine, volume 19, issue 02, 2007, pages 125–129, ISSN [http://www.worldcat.org/issn/0172-4622 0172-4622], doi [http://dx.doi.org/10.1055/s-2007-971894 10.1055/s-2007-971894]</ref>
<ref name="GaesserWilson2008">G. Gaesser, L. Wilson, Effects of Continuous and Interval Training on the Parameters of the Power-Endurance Time Relationship for High-Intensity Exercise, International Journal of Sports Medicine, volume 09, issue 06, 2008, pages 417–421, ISSN [http://www.worldcat.org/issn/0172-4622 0172-4622], doi [http://dx.doi.org/10.1055/s-2007-1025043 10.1055/s-2007-1025043]</ref>
<ref name="HoushHoush1989">Dona J. Housh, Terry J. Housh, Sonja M. Bauge, The accuracy of the critical power test for predicting time to exhaustion during cycle ergometry, Ergonomics, volume 32, issue 8, 1989, pages 997–1004, ISSN [http://www.worldcat.org/issn/0014-0139 0014-0139], doi [http://dx.doi.org/10.1080/00140138908966860 10.1080/00140138908966860]</ref>
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