# The Application of Critical Power, the Work Capacity above Critical Power (W′), and Its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription

^{*}

## Abstract

**:**

## 1. Introduction

_{lim}= A + B × T

_{lim}

_{lim}= limit of work (J); A = fixed energy reserve (J); B = critical power (W); T

_{lim}= time limit (s).

_{2max}). The correlations provided a link between the parameters of the mathematical model and the underlying physiology, suggesting that exercise intensities above CP deplete the fixed energy reserves owing to an insufficient supply of oxygen for aerobic metabolism. Poole, et al. [4], provided further evidence that CP did indeed represent a physiological threshold by demonstrating that intensities above CP did not evoke a $\dot{\mathrm{V}}\mathrm{O}$

_{2}steady state. In this “severe intensity domain” $\dot{\mathrm{V}}\mathrm{O}$

_{2}continued to rise until $\dot{\mathrm{V}}\mathrm{O}$

_{2max}was attained and exhaustion ensued, whilst “heavy intensity domain” exercise performed slightly below CP resulted in the attainment of a $\dot{\mathrm{V}}\mathrm{O}$

_{2}steady state without exhaustion. Despite the simplicity of the CP model and the association of CP with a physiological threshold of sustainable exercise, other measures of aerobic capacity have received arguably more research attention. Lactate turn-point [5], lactate threshold [6], onset of blood lactate accumulation [7], maximal lactate steady state (MLSS) [8], respiratory compensation point [9,10] and ventilatory threshold [6], are all intended to identify or approximate an anaerobic threshold or maximum intensity of steady state exercise through various invasive (blood lactate) and non-invasive (pulmonary gas analysis) procedures. A variety of procedures exist to determine these measures, but most (apart from those to determine MLSS) can be completed within one or two laboratory visits. CP testing, however, requires between two and seven laboratory visits to produce a valid measurement of CP [11], hence it is likely such a demanding schedule of exhaustive tests has impeded the widespread adoption of CP testing, particularly by athletes and their coaches. The advent of the 3-min all-out test [12], was perhaps the catalyst for an upsurge in research investigating and utilizing critical power. The protocol simply required a subject to pedal as fast as possible for the entirety of the three minutes. CP could be interpreted as the levelling of aerobically driven power output during the last 30 s of the test after all anaerobic work or W′ had been spent earlier in the effort. W′ could then be calculated as the total amount of work done above CP during the three minutes. Whilst the test protocol did require a preliminary laboratory visit to tune the test parameters, it offered the physiological and performance-related measures of critical power and W′ in a much less demanding manner than before.

_{2}at CP and $\dot{\mathrm{V}}\mathrm{O}$

_{2max}[18]. Moreover, the magnitude of $\dot{\mathrm{V}}\mathrm{O}$

_{2max}and the development of the $\dot{\mathrm{V}}\mathrm{O}$

_{2}“slow component” within the severe intensity domain have been shown to be determinants of W′ [19]. Latterly, W′ has been associated with the accumulation of fatiguing metabolites such as inorganic phosphates and hydrogen ions [20,21,22], with W′ in a cycling test shown to be reduced immediately following severe upper body exercise, presumably owing to the transport or accumulation of metabolites in the bloodstream [23]. Despite the lack of a clear understanding of the bioenergetics of W′, the parameter continues to be a good predictor of work capacity above CP.

## 2. Assumptions of the Critical Power Model

- The aerobic supply of energy is unlimited for any duration.
- Cycling efficiency remains constant.
- Power output is limited solely by duration and tends towards infinity as time duration approaches 0 s.
- All power output demands up to CP are immediately and constantly fulfilled by aerobic mechanisms up to that limit.
- At exhaustion W′ is fully depleted, i.e., W′ equals 0 J.

_{2max}at the end of exercise, which is a pre-requisite for the complete expenditure of W′ [46,47], minimizing the amount of work completed whilst aerobic metabolism is less than CP, and reducing the opportunity for negative psychological consequences.

## 3. Methods for Determining Critical Power and W′

#### 3.1. Constant Work Rate Tests

^{−1}(Equation (4)).

_{lim}= W′/(P − CP)

_{lim}+ W′

_{lim}) + CP

_{lim}= time limit (s); P = power output (W).

^{2}values [59]. Furthermore, the fit method of the mathematical models results in the derived values of CP being more sensitive to the longer duration trials, and shorter trials having a greater influence on W′. It has also been shown that 30 s all-out efforts immediately following the cessation of TTE trials have yielded an increase of power above CP; a scenario that simply should not be possible after the full depletion of W′ [51]. Furthermore, this study demonstrated that the longer the duration of the TTE the greater the amount of work that could be performed in a subsequent 30 s effort, implying that the longer the TTE the more W′ that is spared. This sparing of W′ particularly over longer trials is likely owing in part to motivational and other psychological factors, which for some time have been a consideration in long TTE trials [60,61]. Perceived exertion has been proposed as the reason for the termination of exercise in TTE trials lasting around 14 min [43], (which is towards the upper end of durations used in CP trials), whilst mentally fatiguing tasks prior to exercise have increased physiological markers during TTE resulting in exercise being terminated earlier [42]. Furthermore, a shift from peripheral fatigue towards central fatigue is found as the duration of exercise increases [62]. As such it is reasonable to assume that the longer the TTE duration the further from complete expenditure of W′ the participant is at the premature termination of exercise. Moreover, given such a scenario the best fit methods would lead to an underestimation of CP and potential overestimation of W′. Validation of laboratory-based CP and W′ estimations from TTE trials against similar field measures comprising self-paced, fixed-duration cycling efforts performed at an outdoor velodrome has established statistical agreement via negligible bias and low within-subject variability of CP values, but not W′, which was on average approximately 5 kJ higher in the field tests [63], indicating a greater amount of work performed.

#### 3.2. Three-Minute All-Out Test

_{2peak}which is then used as an estimate for CP in the subsequent all-out test undertaken on a separate day. The all-out test comprises a short warm-up followed by a 3-min all-out effort where the participant pedals as fast as possible throughout the duration of the test. The resistance of the ergometer is set such that the estimated CP from the preliminary test is attained at the participant’s preferred cadence. The test works on the premise that W′ is fully expended during the first 2.5 min of the test, leaving the power output of the final 30 s to reflect the CP asymptote. That power output is CP during the final 30 s is mathematically shown by Equation (4). Thus, CP is deemed to be the average power output during the final 30 s and W′ is the total work done above CP during the 3-min effort [12]. When combined with the initial determination of the GET, this provides an athlete with a profile of the both the moderate-heavy and heavy-severe intensity domain boundaries along with W′ capacity. Burnley, et al. [12], validated the test by having the participants cycle above and below the measured CP. At a CWR 15 W above CP, participants failed to achieve a steady $\dot{\mathrm{V}}\mathrm{O}$

_{2}and blood lactate measurements rose inexorably until exhaustion, whilst at 15 W below CP the majority of them completed 30 min achieving a $\dot{\mathrm{V}}\mathrm{O}$

_{2}steady state and stable blood lactate levels. Successful validation of CP and W′ derived from the 3-min test against those derived from CWR tests has been subsequently demonstrated [49,67], however the 3-min all-out test reportedly overestimated CP and underestimated W′ when compared to measures derived from time trials in elite cyclists [36], and in trained cyclists [68,69]. However, in the latter studies actual total work done during the 3-min tests far exceeded what the CWR tests would have predicted as possible, suggesting the CWR-derived estimates of CP were low. Moreover, the Bartram, et al. [36], study undertook the CWR tests during a single day without accounting for the incomplete reconstitution of W′ seen within single-day testing [65].

^{−1}greater than that preferred has been shown to significantly reduce the CP measurement derived from the test. The 3-min all-out test relies heavily on the assumption that aerobic metabolism instantly provides energy up to the individual’s CP. That power output peaks within the first 5–10 s of the test [49,68], yet $\dot{\mathrm{V}}\mathrm{O}$

_{2}does not peak until approximately 80 s into the test [12], suggests that the contribution of aerobic metabolism during the first half of the test does not meet the demand hence there is a greater reliance upon anaerobic metabolism, resulting in a possible underestimation of W′. Conversely, during the last 30–60 s of the test where power output seemingly plateaus, small variations in power output above and below CP are observed [69], yielding a small increase to the measured W′ due to the additional work done above CP.

#### 3.3. Ramp All-Out Test

_{2}never attained a steady state. Within the same study measurements of CP and W′ were also compared to those derived from traditional CWR tests, with no mean difference observed between CP, but W′ was significantly smaller in the ramp all-out test. Similarly to CWR and 3-min all-out tests, the ramp test violates the CP model assumption that aerobic metabolism immediately supplies energy up to the limit of CP, however the shallow 20 W∙min

^{−1}ramp slope employed would likely mean a small but continuous depletion of W′ throughout the ramp up to the point around CP, owing to the power output demand increasing and aerobic metabolism responding to the increased demand. Whilst this lag can be described in terms of oxygen kinetics [77,78], the extent of any effect on the measured value of W′ remains difficult to quantify, although in comparison to CWR tests a shortfall of approximately 2.5 kJ in total work done during the ramp has been reported, albeit at a much steeper ramp rate, which the authors attribute to the differences in W′ [79].

_{2}responses and comparisons to a CWR test (described above) [48], suggest this inflation of CP is small if it exists at all. Power output during the all-out phase did not vary between 30 s and 180 s, allowing the testing burden of this phase to be reduced to 2 min in later studies [45]. Additionally, in keeping with the 3-min all-out test, the all-out phase of the power output during the ramp test all-out phase contained a small variation above and below CP, which was included in the determination of W′, potentially inflating it albeit by a small amount given that W′ was expected to be fully expended during the ramp phase. A later variation of the ramp all-out test [45], did not include work done above CP during the 2-min all-out phase when determining the W′, but included a novel step-down in power output at the end of the ramp to 30 W above estimated CP to accommodate the notion that W′ may not be fully expended at the peak of the ramp because of the maximal power at any instant being limited to a proportion of the remaining W′ [31,79]. Similar observations of additional work performed slightly above CP following the apparent limit of tolerance have previously been observed [51,80,81].

_{2max}derived from preliminary tests [12,67].

## 4. W′ Reconstitution

_{2}recovery kinetics (half time = 74 s) and faster than that of blood lactate kinetics (half time = 1366 s) [94]. Like W′, intramuscular PCr depletes when exercise is performed above CP [20], and increases when workload is reduced below CP [80]. That the kinetics of W′ reconstitution and $\dot{\mathrm{V}}\mathrm{O}$

_{2}recovery (measured as a proxy for intramuscular phosphocreatine (PCr) reconstitution, [95]) did not align was suggestive of a process that may be partially dependent upon PCr reconstitution. Examining PCr levels during intermittent single leg exercise above and below CP revealed that the exhaustion of W′ coincided with the same level of PCr depletion regardless of recovery duration and that PCr reconstitution slowed with progressive bouts of intermittent exercise [96]. However, the intermittent protocol used in the study cannot determine W′ during the exercise and, therefore, cannot detect if W′ reconstitution itself slowed alongside that of PCr reconstitution.

_{2max}[99] and the magnitude of the delta between $\dot{\mathrm{V}}\mathrm{O}$

_{2max}and CP [99,100], the underlying physiological determinants of W′ remain largely unknown, necessitating that modelling be conducted on experimental data. Such a model was developed by Skiba, et al. [101], derived from an intermittent cycling protocol of 60 s severe intensity exercise and 30 s at different recovery intensities over four trials. Knowing the initial W′ and assuming exhaustion occurred when W′ was fully depleted, an integration model (henceforth referred to as Skiba1) was developed to predict the W′ balance (Equation (5)).

_{bal}= balance of W′ at time t (J); W′ = initial known W′ (J); W′

_{exp}= total W′ expended (J); t − u = recovery duration (s); τ

_{W′}= W′ reconstitution time constant (s).

_{W′}) was inversely related to CP indicating that those with the highest CP had the faster W′ reconstitution rates. An exponential regression yielded a method of determining τ

_{W′}based on CP (Equation (6)).

_{W′}= 546 × e

^{(−0.01 DCP)}+ 316

_{W″}= W′ reconstitution time constant (s); D

_{CP}= Difference between the known CP and recovery power (W).

_{CP}) beyond which no further advantage is gained during recovery. As only one of the untrained participants had a CP in excess of this figure its validity remains theoretical. The experimental data from which the model was derived manipulated recovery intensity, but not duration. In a follow-up study [102], recovery and work durations varied between 5–20 s and 20–60 s, respectively, however the model underestimated W′ reconstitution in all work-recovery permutations, with the 60 s work and 30 s recovery as used in the original experiment producing the closest match to the predicted outcome. It was also noted that τ

_{W′}, as fitted to the experimental data, varied considerably between individuals possibly due to different muscle-fibre type composition, along with the recommendation that τ

_{W′}be personalized for well-trained cyclists. To validate the Skiba1, the model was retrospectively applied to power data from a single race session, with the competitor abandoning the race when predicted W′

_{bal}was approximately 1.5 kJ [101]. A further validation study using receiver operator curve analysis to separate signal from noise determined that exhaustion defined as a W′ balance of 1.5 kJ appropriately classified 80% of athletes as exhausted [103]. As the study did not actually necessitate participants to ride to absolute exhaustion, a balance of 1.5 kJ may be an appropriate threshold for the continuation of racing and training.

_{W′}has been individually and accurately calculated beforehand.

_{bal}= W′ − [(P − CP) × t]

_{bal}= W′ − W′

_{exp}× e

^{(DCP−t/τW′)}

_{bal}= balance of W′ at time t (J); W′ = W′ at start of bout (J); W′

_{exp}= W′ expended (J); τ

_{W″}= W′ reconstitution time constant (s); t = time (s); D

_{CP}= difference between the known CP and recovery power (W).

^{−1}[106], and the original 60/30 s intermittent cycling protocol was used to successfully validate the model in hypoxia on the condition that CP and W′ parameters were determined at the same hypoxic levels [107]. The application of cycling in hypoxia (such as when ascending a mountain) has been further considered resulting in a prediction equation for CP and W′ at altitude. This was tested using intermittent cycling against both Skiba models, with the Skiba2 model producing the closest match at the point of exhaustion [56]. Notably, both Skiba models were developed following experimental testing of untrained participants with τ

_{W′}observed to be highly variable between participants [101,105]. The validity of the Skiba2 model for W′ reconstituted was assessed against elite athletes and was found to significantly underestimate their W′ reconstitution during intermittent exercise, resulting in the production of a modified τ

_{W′}(Equation (9)) for this athletic population [108]. However, the testing of elite athletes warranted several methodological compromises in establishing CP and W′ parameters from training data rather than exhaustive tests, and recovery between trials was only 20 min. Thus, W′ was unlikely to have fully recovered. Like the Skiba models, the proposed τ

_{W′}was reliant solely upon D

_{CP,}yet the authors noted that increased aerobic fitness was likely to influence W′ reconstitution rates and that greater excess post-oxygen consumption was a probable mechanism for faster recovery [108,109]. A summary of W′ reconstitution studies can be seen in Table 1.

_{W′}= 2287.2 × D

_{CP}

^{−0.688}

_{W″}= W′ reconstitution time constant (s); D

_{CP}= difference between the known CP and recovery power (W).

_{2}, blood lactate or pH measurements at the end of the depleting bout, further complicating the understanding of W′ reconstitution. Despite the criticisms of the Skiba models [45,104,108,110], they remain the only examples published to date.

_{W′}), a stronger relationship with $\dot{\mathrm{V}}\mathrm{O}$

_{2max}existed for W′ reconstitution, along with relationships with both heart rate recovery and excess post-exercise oxygen consumption (EPOC). Relationships were also found between W′ reconstitution and fat mass in both trained and untrained subsets, suggesting a detrimental effect on W′ reconstitution. The slowing of W′ reconstitution following an exhaustive second bout was also inversely related to measures of $\dot{\mathrm{V}}\mathrm{O}$

_{2max}, heart rate recovery and EPOC in the trained subset only. Further insight into the quantification of the influence of these characteristics and their interdependency with training status is needed before models are produced with improved accuracy that can influence race performance (tactics) in real time.

## 5. The Application of Critical Power and W′ for Training Prescription

_{2max}or lactate thresholds, they will know their “functional threshold power” (FTP); a notional threshold power output that is sustainable for one hour [120], which, as a direct measure of performance, is accessible to any cyclist with a commercially available power meter. FTP is described as both analogous to lactate threshold, and similar to critical power in terms of fatigue occurring above the threshold power output [120], despite the physiological differences between these measures. The adoption of FTP as the de facto standard for performance measurement and tracking including amongst professional cyclists [121] has led to recent investigations into its physiological basis. As a measure of endurance performance FTP correlates strongly against other such endurance measures [122,123,124,125,126,127,128], but was not found to be an interchangeable or surrogate measure of lactate threshold [122,125,126,129,130], CP [131], respiratory compensation point [132], or MLSS [124,133] (see Table 2). This is unsurprising given that FTP is a measure of performance over an arbitrary chosen one-hour duration, which sits unquestionably within the confines of the heavy intensity domain, and as such does not align to any known physiological markers, thresholds or boundaries which define such laboratory-derived measurements [13]. Furthermore, to avoid the psychological factors that can affect fatigue over a 60-min trial, FTP is almost always estimated from a shorter 20-min test by scaling average power to 95% [120,121,122,123,124,125,126,129,134], or even an 8- min test scaling average power to 90% [129,130]. Thus, whilst FTP being in the heavy intensity domain will not deplete W′, the value is estimated from test protocols in the severe domain which expend an unknown amount of W′, further questioning its validity as either a performance measure or physiological proxy.

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 1.**Typical power profiles of tests to determine critical power (CP) and W′ (the work capacity above CP). (

**a**) Constant work rate tests to estimate CP as the asymptote of the power-duration relationship, and W′ as the area of the shaded rectangles above CP. (

**b**) 3-min all-out test estimating CP as the average power of the final 30 s and W′ as the total work done above CP. (

**c**) Ramp all-out test estimating CP to as the average power of the final 30 s of the all-out phase, and W′ as the total work done above CP.

Study | Participants | Protocol Description * | Model ^{†} | Principal Findings in Relation to W′ Reconstitution |
---|---|---|---|---|

Bartram, et al. [108] | 4 male; elite cyclists | Intermittent: 30 s work/60 s recovery + open ended severe to finish | Skiba2 | Skiba2 underestimated W′ reconstitution. New W′Tau formula proposed for elite cyclists |

Broxterman, et al. [106] | 6 male | Handgrip repetitions. Tension/relaxation of 50% and 20% duty cycles | Skiba1 | Validated the Skiba1 model over a duty cycle which authors suggested as a proxy for the contraction and relaxation during a pedal revolution. |

Caen, et al. [110] | 11 male; physical exercise (PE) students | 12 trials: 4 and 8 min exhaustive bouts, with 2,4,6 min recoveries | Skiba1 | Skiba1 underestimated W′ reconstitution more so at 2-min recovery, less so at 6 min. Large individual variations in W′Tau. W′ reconstitution affected by preceding depletion rate, slower depletion = less reconstitution |

Chidnok, et al. [93] | 7 male; recreationally active | Intermittent: 60 s work/30 s recovery in differing domains | n/a | No recovery in severe domain. Recovery rate of W′ slower than expenditure in relation to critical power (CP). |

Chidnok, et al. [96] | 9 male; recreationally active | Single leg knee extensions. intermittent 60 s work/18, 30, 48 s recovery | n/a | W′ reconstitution increases with recovery duration. Phosphocreatine and pH levels were always the same at exhaustion. Phosphocreatine recovery correlated to W′ reconstitution but was faster. Phosphocreatine recovery slowed as exercise session progressed. |

Chorley, et al. [45] | 20 (19 male, 1 female; 9 trained, 11 untrained) | Repeated ramps to exhaustion with 2 min recoveries | Skiba1 | Skiba1 did not fit the protocol, overestimate W′ at exhaustion and underestimating reconstitution during recoveries. W′ reconstitution slowed with repeated bouts of exhaustive exercise. |

Chorley, et al. [99] | 20 male; (9 trained, 11 untrained) | Repeated ramps to exhaustion with 2 min recoveries | Skiba1 | Assessment of anthropometric and physiological relationships with W′ reconstitution and its slowing following repeated bouts. |

Felippe, et al. [50] | 10 male; recreationally active | 2 × 6 min constant work rate (CWR) exhaustive bouts separated by 3, 6, 15 min recoveries | n/a | W′ reconstitution compared with neuromuscular recovery. Recovery of voluntary activation faster than W′, no difference between time constants of W′ and maximal voluntary contraction. |

Ferguson, et al. [94] | 6 male; recreationally active | 6 min CWR exhaustive bout then 3, 6, 15 min recoveries | n/a | W′ reconstitution found to be curvilinear. Half-time of W′ reconstitution was faster than that of blood lactate but slower than that of oxygen uptake (a proxy for phosphocreatine reconstitution) |

Morton and Billat [92] | 6 male; well trained | Running: intermittent 60, 180, 30 s work, 60, 180 s recovery | n/a | Produced original model of linear W′ reconstitution at same rate as expenditure in relation to CP. Established W′ reconstitution occurred during recovery due to extended distances covered. |

Shearman, et al. [107] | 11 male; well trained | Intermittent: 60 s work/30 s recovery | Skiba1 | Validated skiba1 in hypoxia with proviso that CP and W′ were also measured at same level of hypoxia |

Skiba, et al. [101] | 7 male; recreationally active | Intermittent: 60 s work/30 s recovery | Skiba1 | Creation of Skiba1 W′bal model based on intermittent exercise to exhaustion, together with generic Tau equation based on CP. Validated against single rider in a race with W′bal of 1.5 kJ at retirement from race. |

Skiba, et al. [103] | 8 (6 male, 2 female) 8 well trained triathletes | Assessment of training and race data | Skiba1 | Validation of Skiba1 on training and race data to detect the point of exhaustion. When exhaustion is set at W′bal = 1.5 kJ prediction of exhaustion was 80% appropriately classified as exhausted and 88% appropriately classified as non-exhausted. Recommendation to use 1.5 kJ as practical level of exhaustion. |

Skiba, et al. [105] | 10 (6 male, 4 female); recreationally active | Intermittent: 60, 40, 20 s work/30, 20, 10, 5 s recovery | Skiba1 | Skiba1 underestimated W′ reconstitution, more so with reduced work and/or recovery durations. Large individual variations in reconstitution rate hence recommendations to individualize Tau. |

Skiba, et al. [102] | 11 (5 male, 6 female); recreationally active | Cycle and single leg knee extensions. 3 min CWR exhaustive bout then 1, 2, 5, 7 min recoveries | Skiba2 | Skiba2 differential model produced allowing real time W′bal prediction. Large inter and intra individual variations in reconstitution rate observed. |

Sreedhara, et al. [104] | 7 male; trained | 120 s bout to deplete 50% of W′, followed by 2, 6, 15 min recoveries, followed by 3-min all-out | Skiba2 | Skiba2 overestimated W′ reconstitution, based on the estimated 50% of W′ expended during initial bout. W′ reconstitution did not increase from 6 min to 15 min recovery hence W′ reconstitution was not exponential. |

Townsend, et al. [56] | 9 male; trained | Intermittent: 40–60 s work/30–60 s recovery | Skiba1 and Skiba2 | Produced a modification equation for CP based on altitude for use in Skiba models to allow W′ reconstitution to be predicted at increasing altitude. |

Vanhatalo and Jones [40] | 7 male; recreationally active | 30 s sprint, followed by 2- or 15- min recovery then 3-min all-out test | n/a | Prior severe sprint exercise (extent of W′ expenditure unknown) depletes W′ but not CP. W′ reconstruction of 79% after 2 min and fully recovered by 15 min |

Vinetti, et al. [111] | 7 male; recreationally active | Incremental ramp with steps 30–300 s duration with recovery between each step of 0–180 s. | n/a | Extensive mathematical representation of discontinuous ramp exercise. |

^{†}The W′ reconstitution model referenced or assessed in the study where Skiba1 is the integration model (Equation (5)) and Skiba2 is the differential model (Equations (7) and (8)).

**Table 2.**Comparisons of functional threshold power to previously validated physiological measurements.

Study | Participants | Functional Threshold Power Test Method | Validated Against * | Mean Functional Threshold Power (W) | Comparison Mean Power Output (W) | Significantly Different | Correlation Coefficient (r) | Comments |
---|---|---|---|---|---|---|---|---|

Barranco-Gil, et al. [132] | 15 male, well trained | 20-min test | RCP | 284 to 286 | 344 ± 32 | Yes | 0.86 to 0.93 | Range of FTP and correlation coefficients due to 3 warm up techniques providing Functional Threshold Power (FTP) values of 286 ± 26 W; 284 ± 26 W; 286 ± 32 W |

Borszcz, et al. [122] | 23 male, trained | 20-min test | IAT | 236 ± 38 | 344 ± 32 | No | 0.61 | Graded test with large 40 W increments used to determine IAT |

60-min test | IAT | 231 ± 33 | 237 ± 29 | No | 0.76 | |||

Gavin, et al. [129] | 7 male, trained and well trained | 8-min test | OBLA | 301 ± 13 | 293 ± 9 | No (see notes) | 0.70 | OBLA selected from three other Lactate measurements as most appropriate comparison for FTP |

Inglis, et al. [124] | 18 (12 male 6 female), trained and well trained | 20-min test | MLSS | 261 ± 45 | 243 ± 48 | Yes | 0.96 | |

Jeffries, et al. [125] | 20 male, well trained | 20-min test | LT (Dmax) | 266 ± 42 | 221 ± 25 | Yes | 0.80 | |

LT (modified Dmax) | 266 ± 42 | 238 ± 32 | Yes | 0.75 | ||||

OBLA | 266 ± 42 | 268 ± 30 | No | 0.88 | authors noted that despite no significant difference between FTP and OBLA, large random error made in individual data meant that FTP was not equivalent to OBLA | |||

IAT | 266 ± 42 | 244 ± 33 | Yes | 0.85 | ||||

Klitzke Borszcz, et al. [123] | 15 male, trained and well trained | 20-min test | MLSS | 252 ± 23 | 248 ± 25 | No | 0.91 | Nine out of 12 participants had difference between MLSS and FTP of 5% or more |

Lillo-Bevia, et al. [133] | 11 male, trained | 20-min test | MLSS | 262 ± 19 | 250 ± 16 | Yes | 0.95 | |

MacInnis, et al. [127] | 8 male, well trained | 60-min test | CP | 309 ± 26 | 325 ± 29 | Yes | 0.91 | Critical power derived from a 4-min and 20-min test, the latter of which is longer than generally accepted for CP testing. |

McGrath, et al. [128] | 19 (12 male 7 female) well trained | 20-min test | LT (Dmax) | 259 ± 40 | 246 ± 38 | Not reported | 0.94 | authors noted large limits of agreement meaning that FTP was not equivalent to Lactate threshold |

Morgan, et al. [131] | 12 male, trained | 20-min test | LT (Dmax) | 278 ± 42 | 275 ± 40 | No | 0.92 | authors noted that despite no significant difference between FTP and CP, large limits of agreement meant that FTP was not equivalent to CP |

Sanders, et al. [130] | 19 male, well trained | 8-min test | LT (DMax) | 341 ± 33 | 279 ± 20 | Very largely different | Not reported | |

LT (modified Dmax) | 341 ± 33 | 319 ± 29 | Moderately different | Not reported | ||||

OBLA | 341 ± 33 | 319 ± 25 | Moderately different | Not reported | ||||

Valenzuela, et al. [126] | 20 male, cyclists | 20-min test | LT (modified Dmax) | 240 ± 35 | 246 ± 24 | No | 0.90 | |

Subset: 11 recreational cyclists | ≈217 | ≈232 | Yes | 0.88 | subgroup power outputs are derived from mean body mass × w/kg for each subgroup as FTP and LT subgroup means are not quoted in the study. | |||

Subset: 9 well trained cyclists | ≈269 W | ≈265 | No | 095 |

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**MDPI and ACS Style**

Chorley, A.; Lamb, K.L.
The Application of Critical Power, the Work Capacity above Critical Power (W′), and Its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription. *Sports* **2020**, *8*, 123.
https://doi.org/10.3390/sports8090123

**AMA Style**

Chorley A, Lamb KL.
The Application of Critical Power, the Work Capacity above Critical Power (W′), and Its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription. *Sports*. 2020; 8(9):123.
https://doi.org/10.3390/sports8090123

**Chicago/Turabian Style**

Chorley, Alan, and Kevin L. Lamb.
2020. "The Application of Critical Power, the Work Capacity above Critical Power (W′), and Its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription" *Sports* 8, no. 9: 123.
https://doi.org/10.3390/sports8090123