CP was determined using a time-trial TT protocol of three durations 12, 7, and 3 min interspersed by 30 min passive rest. Differences between means were examined using magnitude-based inferences and a paired-samples t -test. There was a With relatively large ranges for LoA between variables, these values generally should not be used interchangeably.
Caution should consequently be exercised when choosing between FTP and CP for the purposes of performance analysis. Sport scientists, athletes, and coaches intuitively understand that as exercise intensity increases, a point is reached where a maximal metabolic steady state occurs, beyond which perceptions of effort and physiological perturbations progress more rapidly for review see: Jones et al.
These perceptions of physical discomfort are associated with mechanisms of peripheral fatigue which ultimately lead to task failure Hureau et al.
During laboratory testing this threshold is usually identified using lactate landmarks e. These thresholds are protocol dependent and may not align with a maximal oxidative steady state during constant load exercise, which has thus led to controversy Jamnick et al. Furthermore, mathematical modeling of lactate kinetics suggests that a true equilibrium between maximal whole body lactate production and oxidation in a gradually increasing blood lactate concentration Beneke, Therefore, since the so-called critical power CP has been shown to lie within the intensity region which distinguishes steady state from non-steady state oxidative metabolism Poole et al.
Over the past 40 years, the CP concept has been studied extensively within the scientific literature and it has emerged as a simple mathematical model which not only describes the relationship between sustainable power and the development of fatigue during high intensity exercise, but which also provides an estimate of the maximal sustainable metabolic rate Poole et al.
Nevertheless, there are some methodological considerations which might affect an accurate determination of CP e. The work rate at CP is closely associated with performance in endurance events Kranenburg and Smith, ; Florence and Weir, ; Joyner and Coyle, ; Nimmerichter et al.
Due to the increasing availability of affordable on-the-bike power meters though, field-based methods of threshold assessment have been validated Karsten et al. Additionally, the use of specialized and expensive laboratory equipment is not always justified and it requires technical expertise. More recently, practical methods of threshold assessments have emerged such as field-based CP testing Karsten et al.
However, to-date there is controversy as to whether FTP is related to CP or parameters of other threshold concepts e.
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For example, Valenzuela et al. Using measures of gas exchange, Denham et al. O 2max to be ificantly correlated with FTP. Also, Borszcz et al. The authors concluded that despite strong correlations, the limits of agreement between the FTP estimates and IAnT were too wide to be used interchangeably. A major limitation of some of these aforementioned studies is that FTP was compared to parameters obtained from incremental exercise, which are known to be protocol dependent and may not align with indices like CP or MLSS obtained during sustained constant work rate exercise e.
CP can be determined using maximal self-paced TT efforts. These have been, when compared to the traditional constant power time-to-exhaustion approach, shown to be valid and reliable Galbraith et al.
Only a limited of published studies exist in the scientific literature which examine the relationship between CP derived from different protocols and FTP MacInnis et al. We chose a test protocol for CP assessment that is not different from the traditional constant-work rate approach Triska et al. Informed consent was obtained from all participants after information of the nature and any risks associated with this study were provided.
During visit one, V. O 2peak and MAP were determined during an incremental test. All subjects had experience at conducting TTs, and they were instructed to give a maximum effort for each test. Participants refrained from heavy exercise in the 24 h prior to testing, and food and caffeine for 3 h prior to testing.
For all three visits participants were instructed to arrive at the laboratory in a fully rested and hydrated state. All testing was conducted on a Cyclus2 ergometer RBM Electronics, Leipzig, Germanywhich enables the participant to use their own personal racing bicycle.
After a standardized warm-up at W and for 5 min, participants completed an incremental step test until volitional exhaustion.
Outliers were excluded from further analysis after visual inspection by two independent researchers. MAP was calculated using the following equation:. O 2peak was taken as the highest s rolling-average during the incremental test.
Critical power was determined using maximal self-paced TT efforts over the durations of 12, 7, and 3 min with a 30 min passive rest between efforts. The protocol started with a 5 min warm-up phase at W immediately followed by a switch of the ergometer into TT mode, where resistance increases or decreases as a function of cadence and pedal force.
During the TT, participants were allowed to self-pace via use of a virtual gear changer mounted to the handlebars. Feedback of elapsed time and strong encouragement was provided throughout and participants were asked to produce the highest average PO possible. Heart rate HR was measured continuously and rate of perceived exertion RPE was recorded immediately at the end of trials. HR within 10 beats of age-predicted HR maximum and RPE values above 18 were taken as an indicator for a maximal effort and accepted as a successful test.
The linear PO vs. Functional threshold power was estimated from a single 20 min TT effort similar to recent research Denham et al. Throughout the 20 min TT, participants were allowed to self-pace, and elapsed time feedback was provided as per CP testing. HR was measured continuously and RPE was recorded immediately at the end of trials. Data were first examined for normality using the Shapiro-Wilk test. Table 2. Figure 1. The primary finding of this study was that for moderately trained cyclist, mean CP was non-ificantly higher than FTP i.
Our are supported by Borszcz et al. Furthermore, our are consistent with Valenzuela et al.
Even though using different methods, Borszcz et al. Although Valenzuela et al. Arguably, these findings question the underlying physiology of the FTP concept. With respect to the present study it is noteworthy that Borszcz et al.
Nevertheless, these 6. Collectively, these findings do not support the assertion by Allen and Coggan that FTP always corresponds to the highest the PO maintainable in a quasi-steady state. Importantly, the identified differences and error between CP and FTP values in the present study suggest that these estimates of threshold power should not be used interchangeably.
Interestingly, there were no ificant differences, apart from a trivial effect size, between CP and 20 MMP. These different are suggested to be due to the fact that both CP and MLSS are protocol depended which is a clear limitation. This is also confirmed by the suggestions of Jones et al. The difference in CP and FTP reported here raises another important question, that of which estimate of threshold power more closely aligns with the underlying physiological determinants.
O 2 uptake Korzeniewski and Rossiter, Thus, the most direct non-invasive method of validation is to measure in vivo muscle metabolism slightly above and below the estimate of threshold. To-date, only one study has conducted these measurements using 31 P magnetic resonance spectroscopy during single-leg knee extension exercise Jones et al. The most direct non-invasive method of physiological validation for whole-body exercise is to measure V. O 2 uptake. Several studies have reported the occurrence of a V. O 2 steady state corresponding to a work rate at, or slightly below CP, whereas non-steady state V.
O 2 were observed slightly above CP Poole et al.
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In each case, the limit of tolerance was reached markedly sooner at the work rate slightly above CP. Collectively, these studies provide evidence that estimates of CP correspond to an intensity which demarcates steady state from non-steady state oxidative metabolism.
It should be noted, however, that estimates of CP are protocol dependent e. In fact, it should be expected that predicted MMP over a given duration i. The discrepancy in mean values here is potentially explained by emergence of fatigue mechanisms that are not dominant during the short duration TTs used to estimate CP. For example, central fatigue has been shown to increase during a 20 and 40 km TTs compared to a 4 km TT Thomas et al. There are certain key limitations to the present study. In the absence of pulmonary gas exchange and measurements slightly above and below both CP and FTP, we were unable to validate these estimates according to the physiological criteria which best describes the threshold phenomenon.
Thus, further studies are required to establish the physiological validity of the FTP concept.