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Determination of critical power from a single test
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Science & Sports 23 (2008) 231–238
Basic study
Determination of critical power from a single test夽 Détermination de la puissance critique à partir d’un test unique J. Dekerle a,b,∗ , A. Vanhatalo c , M. Burnley d a
Chelsea School Research Centre, University of Brighton, Gaudick road, BN20 7SP Eastbourne, United Kingdom b Faculty of Sports and Physical Education Sciences, University of Lille-2, Lille, France c School of Sport and Health Sciences, University of Exeter, United Kingdom d Department of Sport and Exercise Science, Aberystwyth University, United Kingdom Received 22 January 2007; accepted 23 June 2007 Available online 24 June 2008
Abstract Aims. – Determination of critical power (CP) from a single test. Current knowledge. – Recent research has been conducted on the utility of all-out exercise to identify parameters of physiological function. This has led to the development of a protocol that would provide a means of measuring CP, that is, the lower boundary for severe exercise, in a single test. Indeed, our recent findings highlight that all-out exercise of 90 s (as the “Wingate” test) are too short for CP to be attained at the end of the exercise while the end power of a 3-min test has been shown to equal CP. The present review presents the methodological considerations to address prior to prolonged all-out exercise testing on cycle ergometers. Prospects. – We conclude by considering the possible applications of our findings to sports performance and the directions for future research in this area. © 2008 Elsevier Masson SAS. All rights reserved. Résumé Objectifs. – Évaluer la puissance critique à l’aide d’un test unique. Actualités. – Plusieurs travaux de recherche ont été conduits sur l’utilité d’un test maximal dans l’identification d’indices physiologiques fonctionnels. Ces travaux ont permis d’établir un protocole permettant de mesurer la puissance critique ou limite inférieure des intensités sévères, à partir de la réalisation d’un seul test. Nos récents résultats mettent en évidence qu’un test maximal de 90 secondes de type « Wingate » est trop court pour permettre l’atteinte de puissance critique en fin d’exercice, alors que la puissance de fin d’exercice, lorsqu’elle s’étend jusqu’à trois minutes, équivaut à la puissance critique. Dans cette revue de littérature, nous présentons les points méthodologiques à considérer lors de la mise en application de ce type de test d’effort. Perspectives. – Nous terminons en proposant des applications possibles de nos recherches dans le domaine pratique et proposons de nouvelles perspectives de recherche. © 2008 Elsevier Masson SAS. All rights reserved. Keywords: Critical power; End-power test; All-out exercise Mots clés : Puissance critique ; Puissance de fin d’exercice ; Test Wingate
1. Introduction
夽 ∗
Présentée au colloque « Puissance critique » Lille, 22 et 23 juin 2007. Corresponding author. E-mail address: [email protected] (J. Dekerle).
0765-1597/$ – see front matter © 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.scispo.2007.06.015
It is reasonably well established that the intensity of exercise can be described in terms of “domains”. Exercise performed strictly within any one of these domains results in characteristic physiological response profiles [10] and the tolerable duration of exercise is predictable when these domains are taken into account. Therefore, the measurement of the boundary between
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each exercise intensity domain is fundamental for optimizing training designs. The lactate threshold has been convincingly demonstrated to demarcate the moderate and heavy intensity domains [2], while critical power (CP) has been suggested to demarcate the heavy and severe intensity domains [42]. Incremental exercise provides the means to measure the lactate threshold and the maximal oxy˙ 2max ), but attempts to use this form of testing to gen uptake (VO identify the boundary between heavy and severe intensity exercise have been either unsuccessful [9] or, from a physiological standpoint, unconvincing [12]. Because the determination of CP requires repeated bouts of exercise with considerable recovery periods between them [23], a single-test determination of CP would be of great practical utility. In our laboratories, the utility of all-out exercise to identify parameters of physiological function has been a major research focus and this has recently led to a protocol that would provide a means of measuring CP in a single test. In the present review, we will address these recent findings and also highlight the methodological considerations required for prolonged all-out exercise testing. We conclude by considering the possible applications of our findings to sports performance and the directions for future research in this area. 2. Applying the CP concept to all-out exercise 2.1. Origin of the CP concept In 1960, a first simple two-parameter model was proposed by Scherrer and Monod [45] to characterize the work of a single local muscle pushed to exhaustion. Participants sustained several constant load tests up to exhaustion and a linear relationship was found between work (W) and time to exhaustion (t) (Eq. (1); Panel B, Fig. 1). The y-intercept was associated to a reserve of work (W ) the authors showed measurable under occlusion. The slope, originally named “threshold of local fatigue” and then “critical power”, was defined as the “maximum rate of reconstitution of the energetic potential of muscular contraction”. The numerous post hoc interpretations of the slope and the y-intercept of the W-t relationships these last 50 years have permitted a better understanding of their physiological meanings although the original definitions of Scherrer and Monod (1960) were far from erroneous.
Several reviews address issues and provide guidelines for determining CP on cycling ergometers [16,23]. Three to five tests have to be performed up to exhaustion, their duration ranging from 2 to 15 min. Subjects can be asked to race over time (the dependent variable being the work rate) or to maintain a given preset power output to exhaustion (time is here the dependent variable). The modelling of the overall power output profile will provide an estimation of CP (Fig. 1). 2.2. Physiological meaning of CP To better understand the physiological meaning of these two parameters, it might be worth considering one of its equivalent models, the hyperbolic P-t relationship. Indeed, CP is also represented by the asymptote of the P-t relationship (Panel A, Fig. 1) and is therefore mathematically defined as the power that can be maintained indefinitely (Fig. 1, Panel A). Accordingly, it was firstly thought that CP was sustainable for a “very long” period of time [18,39]. However, continued increases in blood lactate concentration, oxygen uptake and other physiological parameters (rather than the expected steady-state behaviour) have been observed during trials performed on ergometer at CP and exhaustion times ranging from 18 to 60 min have been recorded [6,28,35]. Moreover, CP has been shown to be higher than the maximal power maintainable without a substantial increase in blood lactate concentration [12,43]. The first belief that CP was sustainable for a very long period of time was a misinterpretation of its mathematical and not physiological definition. We would argue that “indefinite” (not “infinite”) represents the correct term to describe the tolerable duration of exercise at or below CP, since the power–duration relationship “cannot be used to define” the duration of exercise under these conditions. In contrast, the assertion that the tolerable duration of exercise “should be infinite” at CP is clearly at odds with common knowledge. Recently, a few studies attempted to affine the definition of CP by investigating the ˙ 2max can be attained [24,25]. It intensity domains at which VO was demonstrated that CP represented the highest intensity that ˙ 2max , is sustainable for a prolonged duration without eliciting VO that is, the lower boundary for severe exercise [17]. Accordingly, ˙ 2max , despite a some authors observed a nonattainment of VO ˙ 2 slow component during exercise performed at CP [6,42]. VO More recently, the metabolic responses to exercise above and
Fig. 1. Illustration of three different, but equivalent representations of the two-parameter model.
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below CP have been described using 31 P magnetic resonance spectroscopy. Jones et al. [51] demonstrated that work rates below CP resulted in the stabilisation of muscle phosphorylcreatine (PCr), pH and inorganic phosphate (Pi), whereas above CP, PCr declined until exhaustion ensured. Importantly, this PCr response would, during whole body exercise, be expected to be ˙ 2 with time until VO ˙ 2max mirrored by a continued increase in VO is attained, consistent with the above definition. 2.3. Physiological meaning of anaerobic work capacity That W represents an “anaerobic” capacity for work has been inferred by its lack of response to ischemia, hypoxia and hyperoxia [39], but its decrease in response to muscle glycogen depletion [38] and its increase in response to high-intensity training in untrained subjects [31] and creatine monohydrate supplementation [37]. It is also well correlated with numerous surrogate indices of anaerobic work capacity, such as the maximal accumulated oxygen deficit (MAOD; [36]) or the work performed during predominantly anaerobic exercises [13,22,26,30,46]. Heubert et al. [52] recently demonstrated an effect of a 7-s sprint postperformance test on the y-intercept of the P-t relationship decrease by 30 to 40%, while the slope was unaffected. The second parameter of the CP concept is mathematically defined as a finite reserve of energy store available preexercise [45]. Since the “notion” of anaerobic capacity is a theoretical construct itself [21], its measurement in unit of work is fraught with measurement errors. Therefore, the investigation of the nature of the second parameter of the CP concept remains difficult. However, there is some scientific evidence of its anaerobic nature. For clarity in the presentation, and for consistency with previous work, this second parameter will be abbreviated W . 2.4. Application of the CP concept to all-out exercise It has been suggested that the CP concept can be used to estimate the aerobic and anaerobic energetic contribution to any exercise performed up to exhaustion and of sufficient duration ˙ 2max to be attained [16]. It indeed assumes that the total for VO work done during an exhaustive exercise performed within the severe intensity domain (Fig. 1, Panel B, see Eq. (1)) is equal to the sum of a fixed capacity of anaerobic work (W ) and the work derived from aerobic metabolism solicited at its maximum (CP × t). The research work, recently conducted within our laboratories on the use of all-out test as a means of measuring CP, is based on the assumption that the CP concept is applicable to all-out exercise. During the early part of an all-out effort, W would be highly taxed to enable peak power to be developed in the first couple of seconds. The rapid utilisation of PCr (first few seconds) and glycolytic flux enable a very high rate of ATP resynthesis. The work rate would peak and then systematically decrease, partly due to the decline in the rate of ATP resynthesis from both substrates. The decrement would become less dramatic with time as the substrate oxidation would make the most significant, if not the main contribution to the ATP production [34].
Fig. 2. Schematic of the decrement of work rate during an all-out test up to the attainment of critical power (W , the anaerobic work capacity).
According to the CP concept, the continuous taxation of W during the exercise should lead to its total exhaustion, the endpower output being then equal to CP. The third equivalent of the W-t relationship (Fig. 1; Panel C) could be introduced to support the demonstration. Because power output is a function of the inverse of time (1/t), with CP and W being respectively the y-intercept and the slope of the relationship, when W is finally fully utilised (and equal to zero), according to the CP concept, the remaining power that is developed at the end of the exhaustive all-out test, should equal to CP (Eq. (1)). P = CP + W /t = CP + 0/t = CP
(1)
It is interesting to notice that the shape of a power-output profile obtained from the performance of an all-out exercise, such as the traditional 30-s Wingate test is very similar to the hyperbolic P-t relationship the CP concept is based on (Fig. 2). Crucially, however, the extrapolation of the power-output profile from a 30 s all-out test cannot be used to predict the power output at the conclusion of the fatigue process. Thus, the Wingate-power profile could support a variety of descriptions, ranging from the attainment of a wholly aerobic-power output (i.e., associated ˙ 2max ; [11]) to a continued fall to exhaustion. Our predicwith VO tion, however, is that the power output would ultimately attain the CP [5,7,47]. 3. All-out test – methodological considerations 3.1. Type of cycle ergometer Mechanically-braked cycle ergometers (such as Monarks; Monark Exercise AB, Sweden) are widely and traditionally used for maximal all-out test, such as the 30-s Wingate test [29]. The resistance or load to be applied against the flywheel is based on the individual body mass while considering that the optimal resistance for maximising power output varies depending on gender, age and fitness characteristics of the individual [29]. After warming up, the subject is instructed to pedal as rapidly as possible against zero resistance (in reality this is the resistance offered by flywheel inertia, the moving limbs and frictional components of the drive chain). The braking force is
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then applied as quickly as possible, with simultaneous activation of the timing process. After the load is applied, the subject continues to pedal, remaining in the seated position, as hard and fast as possible for the preset period of time (traditionally 30 s). Flywheel revolutions (or cadence) are counted (usually over intervals of 1 to 5 s) and the resistance being known, the rate of work developed throughout the test can be subsequently calculated. The Schoberer Rad Messtechnik (SRM) training system (science model powermeter, power control and computer software) provides a mean of recording power output at the crank. The cranks – it is equipped of indeed – enable the torque to be measured in the chain ring with either two, four or eight (previously 20) strain gauges, depending on the model. Torque and angular velocity data are transmitted by induction from the crank to a unit on the handlebar that converts the data to power (see [1] for more details). The SRM system has been shown to provide a valid and reliable measure of power when compared with a Monark cycle ergometer [32]. The stationary SRM ergometer enables all-out test to be run under an isokinetic mode. A cadence is imposed and controlled during the test and therefore, needs to be preset [33]. Thirty seconds before the start of the test, the subject is introduced to pedal at a slightly higher cadence (preset value + 3–5 rpm). A countdown of the last 5 s preceding the start of the all-out effort will enable the subject to push as hard as possible from the first second to the end of the test. Torque data will be measured and power calculated accordingly. Controlling the cadence during the all-out test can enriched a research design (i.e. control of the frequency of muscle contraction; consistency in the range of cadence used across a set of tests; maximisation of the total-work rate [33]). 3.2. Reliability A test cannot be considered valid if it is not reliable. Random or systematic errors in the measurement of an all-out performance can come from the cycle ergometer in use (see [41] for more details) as well as the testing itself [27]. The degree of reliability of the traditional 30-s Wingate test, performed on mechanically-braked cycle ergometers, has been widely investigated [29], while the isokinetic mode has not been such a matter of interest. We addressed this issue by looking at the reproducitibility of the power-output profile of a 90-s all-out cycling test [15]. We found peak power (1 s) to be variable between two tests evidenced by a systematic bias from test 1 to test 2 (+ 6%) and a random error of 15%. A heteroscedastic error in this measurement with higher within-subjects differences for subjects of higher peak-power values was also depicted. The higher sampling rate and therefore, higher sensitivity of measurement, could have led to the conclusion that isokinetic all-out tests are not as robust in examining peak power as previously demonstrated on friction-braked ergometers [1]. We noted that when expressed as a 5-s average, peak power was then more reliable (random error decreased to 4.6% compared to 15% with a 1-s average).
Fig. 3. Power output profiles of two subjects of similar mean powers, but with different peak powers (PP1, peak power of subject 1; PP2, peak power of subject 2) and different end powers (EP1, end power of subject 1; EP2, end power of subject 2).
The mean power over the 90 s of the test was found to be extremely robust as previously reported [27], although the test–retest variability in this measure was shown to increase with increasing values. The heteroscedastic error detected could be likened to those detected for peak power. As opposed to peak power and mean power, end power (last 10 s) did not present any heteroscedastic error in the measurement. Its systematic bias was the smallest one compared with those of the three other variables (+ 1.8%) and the random error was only equal to 9.7%. Finally, low intra-individual (a 7.6% random error) of the fatigue index was observed (64 ± 8% and 65 ± 9% for test 1 and 2, respectively). Ratio limits of agreement suggested that a repeated measurement might be expected in 95% of cases to be between 0.92 to 1.21 times the initial peak power measurement and 0.97 to 1.07 times the initial mean power measurement. The 95% limits of agreement for end power and fatigue index were 1.8 ± 9.7% and 2 ± 7.6% of the mean, respectively. It was concluded that the 90-s all-out test would be reliable for given aspects of the physiological profile, with the exception of peak power. Fig. 3 exemplifies the power-output profile of two different subjects. Peak power, mean power over the first 30, 60, and 90 s of exercise and end power (last 30 s of exercise) were also found to be reliable in children [49]. 3.3. Effects of cadence It has long been known that altering movement frequency can profoundly influence the mechanical and physiological responses to exercise. All-out tests are particularly susceptible to the influence of cadence because they are often utilized to measure divergent physiological parameters. The Wingate test is a prime example, wherein a great deal of effort has been made to
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“optimize” the Wingate protocol. In so doing, the braking force required to achieve the highest peak-power output is established and then applied during the test (usually considerably higher than the “standard” 7.5% of bodymass). However, as the test progresses, the flywheel resistance can place the subject at a considerable disadvantage later in the test. In other words, the resistance may well be “optimal” for the attainment of a peakpower output, but it may be suboptimal for all other measured parameters. This is due to the power–velocity relationship of the musculature involved in cycling. The rapid decline in power (and cadence) results the subject’s cadence very rapidly deviating from optimal as the test progresses and as a result the subject “underperforms” the test. This is a serious concern for all-out exercise and, because the range of power output is so large for these kinds of tests, the solution is not straightforward. Choosing isokinetic testing eliminates the change in cadence as the test progresses, but because the power–velocity relationship is known to change as fatigue ensues [44], the cadence is once again only fleetingly optimal. A fixed resistance and variable cadence may, as discussed above, not be truly optimal at any point in the test, but may at least be close to optimal. Our research groups have adopted both approaches due for the most part to the ergometer available for testing (Lode versus SRM). The 3-min all-out test has to date been performed using the Lode Excalibur Sport ergometer and for sprint work, this ergometer is placed in its cadence dependant mode (where power = linear factor × cadence2 ). In designing the test, we were most interested in the power at the end of the test and not the beginning and so we purposefully adopted a strategy of setting the linear factor in such a way that if the subject’s preferred cadence (usually 80 to 90 rpm) was attained, this would happen ˙ 2max at a power output equal to 50% (that is, GET + [0.5 × VO − GET]). One immediate concern was that the resistance set is entirely dependent on what the subject chooses as their preferred cadence. Consequently, we designed a study to investigate the influence of the adoption of different preferred cadences to determine if the power profile of the test and the parameters derived would be altered. Our results showed a small reduction (∼ 9 W) in the end-test power (EP) output when cadence was increased (by 10 rpm above preferred), but not when a similar reduction from the preferred cadence was adopted [48]. However, both the peak-power output and the amount of work done above the EP output were systematically affected: higher cadences reduced these parameters, whereas lower cadences increased them. This, we suggested, could be explained by the power–velocity relationship, because the peak cadence achieved in the high cadence trial was 155 ± 12 rpm and would, therefore, have placed the subjects on the descending limb of the relationship. At the end of the test, when the fatigue processes had reduced and flattened the parabolic power–velocity relationship, the influence of cadence manipulation on power output would have been much smaller, although still evident for the highest cadence studied [48]. Interestingly, these findings suggest that all-out exercise can provide insight into the power–velocity relationship as well as the power–duration relationship (see below).
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4. Recent findings 4.1. The 90-s test – data showing the end-test power to be higher than CP The contribution of both the anaerobic and aerobic pathways to the total-energy release during the performance of an all-out test remains under scrutiny [3,4,40]. It has recently been estimated that 40 to 50 s would be the time required for endurance-trained cyclists to utilize the totality of their anaerobic capacity during an all-out test performed in normoxia [8]. Accordingly, previous findings demonstrated that in predominantly aerobically-trained subjects, the oxygen deficit is smaller during 45-s when compared to 60- and 90-s, but tends to plateau after 60 s of all-out exercise performed on an air-braked ergometer [50]. These findings were later confirmed in a sample of active male [20]. Evaluation of the 90-s test further indicated that maximal or near-maximal (98%) anaerobic-energy release was achieved in 60 s. Based on previous findings, we thought that 90 s would be of sufficient duration to completely exhaust the W , and for CP to be attained at the end of the all-out test (Fig. 2). We designed a study to establish the validity of the 90-s all-out test for the determination of both maximal and submaximal indices of aerobic fitness. We hypothesized that the peak-oxygen uptake at ˙ 2max attained in a ramp the end of the 90-s trial and the VO exercise would be equal. Furthermore, we hypothesized that the power output attained at the end of the all-out test would equate to the individual’s CP [5]. Sixteen subjects (12 men and four women; mean ± S.D.; age: 30.4 ± 6.1 years; weight: ˙ 2max : 3.9 ± 0.7 L−1 ) firstly completed a ramp 69.6 ± 9.9 kg; VO ˙ 2max (5 W/min). Secondly, test to exhaustion to determine VO CP was determined from three separate constant-load tests to exhaustion (exhaustion times ranging from 2 to 15 min). Finally, each subject underwent two separate 90-s all-out efforts. ˙ 2max was not attained at the end of a It was found that VO ˙ 2max ) and even under the condi90-s all-out test (88% of VO tions of considerable fatigue at the end of this test, the final power output was in excess of the individual’s CP (equating ˙ 2max and percentage of CP; Fig. 4). Therefore, 94% of P – VO our hypothesis that there would be agreement between our mark˙ 2max ers of maximal and submaximal aerobic capacity (the VO and CP of the 90-s all-out test, respectively) determined independently and together within a single 90-s all-out test was not supported. A high correlation was obtained between end power and CP (R = 0.86), highlighting that these two variables could be related. The power output during the 90-s test declined below CP for two of the 16 subjects (− 30 and − 34 W). For three other subjects, the difference between end power and CP was lower than 8 W (representing 3% of CP). It was hypothesized that a test of longer duration would allow CP to be attained. 4.2. The 3-min all-out test: measuring CP in a single test Although the 90 s all-out test end-power appears to overestimate CP, it did provide additional evidence that such prolonged all-out exercise is a reliable exercise test. Moreover, the power
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Fig. 4. Critical power (± 95% confidence interval) and end-power values for each participant.
output attained at the end of the test was certainly below that ˙ 2max during an exhaustive ramp test [5,14]. required to attain VO Our investigations in Aberystwyth led to the adoption of a 3-min all-out cycling test against a fixed resistance in an attempt to determine CP. Our first experimental study provided promising initial evidence that the boundary between heavy- and severeintensity exercise may indeed be estimated by all-out exercise [7]. In this work, we determined the 3-min test end-power
Fig. 6. Agreement between the 3-min all-out test end-power and CP from 10 subjects [47]. Dashed line represents the line of identity.
˙ 2 and blood [lactate] responses to and then measured the VO exercise performed 15 W above (presumably severe) and 15 W below (presumably heavy) the EP. Nine of the 11 subjects tested completed 30 min of exercise 15 W below the EP output and ˙ 2 and blood [lactate] seven subjects did so with steady state VO responses. In contrast, none of the subjects completed 30 min ˙ 2 and blood [lacof exercise 15 W above the EP, and the VO tate] responses indicated that all subjects were exercising in the severe-intensity domain [7]. We concluded that the EP is likely to be equivalent to the CP, but that further work was necessary to compare these parameters directly. In a subsequent paper, we tested the hypothesis that the CP and the EP measured in a 3-min test would be equivalent [47]. To do this, we defined the power duration relationship in 10 subjects using five predicting trials of exhaustive exercise and compared the CP and W to the EP and the “work done above end-test power” (WEP), respectively. As shown in Figs. 5 and 6, there was a very close agreement between the parameters estimated “traditionally” from five predicting trials and those estimated from the 3-min all-out test. These results seem so unambiguous that we remain somewhat surprised that in spite of the fact that Monod and Scherrer (1965) explicitly stated that CP cannot be measured during a single bout of exercise, it took more than 40 years for anybody to ask “is that so?”! More importantly, the answer to that question is a resounding “no!” and thus, the 3-min all-out test provides a potentially very efficient and widely applicable means of determining crucial parameters of the physiology of exercise that are often overlooked (or at least not measured) by most of the research community. 5. Applications and future directions
Fig. 5. The CP estimated from the 1/time model (top panel) and the power profile during the 3-min all-out test (bottom panel) in a representative subject. Note the close agreement between the parameter estimates derived from each method.
The analysis of a power-output profile from the performance of an all-out test was originally proposed to assess the anaerobic power and capacity of an individual [29]. Recent studies conducted in our laboratories led to the conclusion that maximal and submaximal indices of aerobic fitness can also be derived from such a performance. Indeed, the sole perfor-
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˙ 2max and CP to be mance of a 3-min all-out test allows VO attained. This should be considered when profiling athletes in laboratories for consultancy or research purposes. Moreover, the several studies recently conducted on the 90-s and 3-min all-out tests offer a new insight into the energetic contribution to all-out effort, using our current understanding of the CP concept. Their outcomes could directly affect training and coaching interventions in specific sports, such as track cycling where power-output profiles are close to those of all-out exercise [19]. Our two laboratories have recently investigated the effect of two different interventions on both CP and the end power of an all-out test. It was hypothesised that the effects of moderate normobaric hypoxia and aerobic training would be of similar magnitude on these two variables, if the two were causally linked. We should soon publish the results of these two studies. We have recently conducted a study on the power-output profiles of paediatric populations (CP concept and 90-s all-out test) and are hoping publishing the main findings in the coming months. These recent findings should lead to a better understanding of exercise tolerance across environmental conditions, levels of fitness and adult versus children. 6. Conclusions Critical power represents the highest intensity that is sustain˙ 2max , that is, able for a prolonged duration without eliciting VO the lower boundary for severe exercise and its measurement is fundamental for optimizing training designs. It is traditionally determined from the performance of several maximal constantload efforts. Recent studies, conducted within our laboratories, demonstrated that the performance of a single all-out test of sufficient duration to totally exhaust the anaerobic work capacity enables CP to be accurately measured. “Linear” (isotonic) as well as isokinetic modes can be used to obtain the poweroutput profile of an individual’s all-out effort and the choice of one of the two modes will depend on the purpose of the testing and cycle ergometer availabilities. It is hoped that the recommendations mentioned in the present article will well guide any researcher or laboratory instructor willing to use these all-out tests for individual profiling. Further publications should follow the present review on the use of all-out exercise in measuring CP. References [1] Balmer J, Bird S, Davison RC, Doherty M, Smith P. Mechanically braked Wingate powers: agreement between SRM, corrected and conventional methods of measurement. J Sports Sci 2004;22(Suppl. 7):661. [2] Barstow TJ, Casaburi R, Wasserman K. O2 uptake kinetics and the O2 deficit as related to exercise intensity and blood lactate. J Appl Physiol 1993;75(Suppl. 2):755. [3] Beneke R, Hutler M, Leithauser RM. Anaerobic performance and metabolism in boys and male adolescents. Eur J Appl Physiol 2007; 101(Suppl 6):671. [4] Beneke R, Pollmann C, Bleif I, Leithauser RM, Hutler M. How anaerobic is the Wingate anaerobic test for humans? Eur J Appl Physiol 2002;87(Suppl. 4–5):388.
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[5] Brickley G, Dekerle J, Hammond AJ, Pringle J, Carter H. Assessment of maximal aerobic power and critical power in a single 90-s isokinetic all-out cycling test. Int J Sports Med 2007;28(Suppl. 5):414. [6] Brickley G, Doust J, Williams CA. Physiological responses during exercise to exhaustion at critical power. Eur J Appl Physiol 2002;88(Suppl. 1–2):146. [7] Burnley M, Doust JH, Vanhatalo A. A 3-min all-out test to determine peak oxygen uptake and the maximal steady state. Med Sci Sports Exerc 1995;38(Suppl. 11). [8] Calbet JA, De Paz JA, Garatachea N, Cabeza de Vaca S, Chavarren J. Anaerobic energy provision does not limit Wingate exercise performance in endurance-trained cyclists. J Appl Physiol 2003;94(Suppl. 2):668. [9] Carter H, Jones AM, Doust JH. Effect of incremental test protocol on the lactate minimum speed. Med Sci Sports Exerc 1999;31(Suppl. 6):837. [10] Carter H, Pringle JS, Jones AM, Doust JH. Oxygen uptake kinetics during treadmill running across exercise intensity domains. Eur J Appl Physiol 2002;86(Suppl. 4):347. [11] Davies CT, Sandstrom ER. Maximal mechanical power output and capacity of cyclists and young adults. Eur J Appl Physiol Occup Physiol 1989;58(Suppl. 8):838. [12] Dekerle J, Baron B, Dupont L, Vanvelcenaher J, Pelayo P. Maximal lactate steady state, respiratory compensation threshold and critical power. Eur J Appl Physiol 2003;89(Suppl. 3–4):281. [13] Dekerle J, Brickley G, Hammond AJ, Pringle JS, Carter H. Validity of the two-parameter model in estimating the anaerobic work capacity. Eur J Appl Physiol 2005;93(Suppl. 3):257. [14] Dekerle J, Brickley G, Hammond AJ, Pringle JS, Carter H. Validity of the two-parameter model in estimating the anaerobic work capacity. Eur J Appl Physiol 2006;96(Suppl. 3):257. [15] Dekerle J, Hammond A, Brickley G, Pringle J, Carter H. Reproducibility of variables derived from a 90 s all-out effort isokinetic cycling test. J Sports Med Phys Fitness 2006;46(Suppl. 3):388. [16] di Prampero PE. The concept of critical velocity: a brief analysis. Eur J Appl Physiol Occup Physiol 1999;80(Suppl. 2):162. [17] Gaesser GA, Poole DC. The slow component of oxygen uptake kinetics in humans. Exerc Sport Sci Rev 1996;24:35. [18] Gaesser GA, Wilson LA. Effects of continuous and interval training on the parameters of the power-endurance time relationship for high-intensity exercise. Int J Sports Med 1988;9(Suppl. 6):417. [19] Gardner AS, Martin JC, Martin DT, Barras M, Jenkins DG. Maximal torque- and power-pedaling rate relationships for elite sprint cyclists in laboratory and field tests. Eur J Appl Physiol 2007;101(Suppl. 3):287. [20] Gastin PB, Lawson DL. Variable resistance all-out test to generate accumulated oxygen deficit and predict anaerobic capacity. Eur J Appl Physiol Occup Physiol 1994;69(Suppl. 4):331. [21] Green S, Dawson B. Measurement of anaerobic capacities in humans. Definitions, limitations and unsolved problems. Sports Med 1993;15(Suppl. 5):312. [22] Green S, Dawson BT, Goodman C, Carey MF. Y-intercept of the maximal work-duration relationship and anaerobic capacity in cyclists. Eur J Appl Physiol Occup Physiol 1994;69(Suppl. 6):550. [23] Hill DW. The critical power concept. A review. Sports Med 1993;16(Suppl. 4):237. [24] Hill DW, Ferguson CS. A physiological description of critical velocity. Eur J Appl Physiol Occup Physiol 1999;79(Suppl. 3):290. [25] Hill DW, Poole DC, Smith JC. The relationship between power and the ˙ 2max . Med Sci Sports Exerc 2002;34(Suppl. 4):709. time to achieve. VO [26] Hill DW, Smith JC. A comparison of methods of estimating anaerobic work capacity. Ergonomics 1993;36(Suppl. 12):1495. [27] Hopkins WG, Schabort EJ, Hawley JA. Reliability of power in physical performance tests. Sports Med 2001;31(Suppl. 3):211. [28] Housh DJ, Housh TJ, Bauge SM. The accuracy of the critical power test for predicting time to exhaustion during cycle ergometry. Ergonomics 1989;32(Suppl. 8):997. [29] Inbar O, Bar-Or O, Skinner JS. In: Washburns RA, editor. The Wingate anaerobic test. Champaign: Human Kinetics; 1996. p. 120. [30] Jenkins DG, Quigley BM. The y-intercept of the critical power function as a measure of anaerobic work capacity. Ergonomics 1991;34(Suppl. 1):13.
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[31] Jenkins DG, Quigley BM. The influence of high-intensity exercise training on the Wlim-Tlim relationship. Med Sci Sports Exerc 1993;25(Suppl. 2):275. [32] Jones AM, Passfield L. The dynamic calibration of bicycle power measuring cranks. In: The engineering of sports. Haake SJs. Oxford: Blackwell Science; 1998. p. 265–74. [33] MacIntosh BR, Svedahl K, Kim M. Fatigue and optimal conditions for short-term work capacity. Eur J Appl Physiol 2004;92(Suppl. 4–5):369. [34] Maughan R, Gleeson M, Greenhaff PL. Metabolic responses to highintensity exercise. In: Biochemistry of exercise and training. Oxford: Oxford university press; 1997. p. 138–57. [35] McLellan TM, Cheung KS. A comparative evaluation of the individual anaerobic threshold and the critical power. Med Sci Sports Exerc 1992;24(Suppl. 5):543. [36] Medbo JI, et al. Anaerobic capacity determined by maximal accumulated O2 deficit. J Appl Physiol 1988;64(Suppl. 1):50. [37] Miura A, Kino F, Kajitani S, Sato H, Fukuba Y. The effect of oral creatine supplementation on the curvature constant parameter of the power-duration curve for cycle ergometry in humans. Jpn J Physiol 1999;49(Suppl. 2): 169. [38] Miura A, Sato H, Sato H, Whipp BJ, Fukuba Y. The effect of glycogen depletion on the curvature constant parameter of the power-duration curve for cycle ergometry. Ergonomics 2000;43(Suppl. 1):133. [39] Moritani T, Nagata A, deVries HA, Muro M. Critical power as a measure of physical work capacity and anaerobic threshold. Ergonomics 1981;24(Suppl. 5):339. [40] Ogura Y, Katamoto S, Uchimaru J, Takahashi K, Naito H. Effects of low and high levels of moderate hypoxia on anaerobic energy release during supramaximal cycle exercise. Eur J Appl Physiol 2006;98(Suppl. 1): 41. [41] Paton CD, Hopkins WG. Tests of cycling performance. Sports Med 2001;31(Suppl. 7):489.
[42] Poole DC, Ward SA, Gardner GW, Whipp BJ. Metabolic and respiratory profile of the upper limit for prolonged exercise in man. Ergonomics 1988;31(Suppl. 9):1265. [43] Pringle JS, Jones AM. Maximal lactate steady state, critical power and EMG during cycling. Eur J Appl Physiol 2002;88(Suppl. 3):214. [44] Sargeant AJ. Human power output and muscle fatigue. Int J Sports Med 1994;15(Suppl. 3):116. [45] Scherrer J, Monod H. Le travail musculaire local et la fatigue chez l’homme. J Physiol 1960;52(Suppl. 2):420. [46] Vandewalle H, Kapitaniak B, Grun S, Raveneau S, Monod H. Comparison between a 30-s all-out test and a time-work test on a cycle ergometer. Eur J Appl Physiol Occup Physiol 1989;58(Suppl. 4):375. [47] Vanhatalo A, Doust JH, Burnley M. Determination of critical power using a 3-min all-out cycling test. Med Sci Sports Exerc 2007;39(Suppl. 3): 548. [48] Vanhatalo A, Doust JH, Burnley M. Robustness of a 3-min all-out cycling test to manipulations of power profile and cadence in humans. Exp Physiol 2007;93(Suppl. 3):383. ˙ 2 during [49] Williams CA, Ratel S, Armstrong N. Achievement of peak VO a 90-s maximal intensity cycle sprint in adolescents. Can J Appl Physiol 2005;30(Suppl. 2):157. [50] Withers RT, Van der Ploeg G, Finn JP. Oxygen deficits incurred during 45, 60, 75 and 90-s maximal cycling on an air-braked ergometer. Eur J Appl Physiol Occup Physiol 1993;67(Suppl. 2):185. [51] Jones AM, Wilkerson DP, DiMenna F, Fulford J, Poole DC. Muscle metabolic responses to exercise above and below the “critical power” assessed using 31P-MRS. Am J Physiol Regul Integr Comp Physiol 2008;294(Suppl. 2):R585. [52] Heubert RA, Billat VL, Chassaing P, Morton RH, Koralsztein JP, di Prampero PE. Effect of a previous sprint on the parameters of the work-time to exhaustion relationship in high intensity cycling. Int J Sports Med 2005;26(Suppl. 7):583.
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Basic study
Determination of critical power from a single test夽 Détermination de la puissance critique à partir d’un test unique J. Dekerle a,b,∗ , A. Vanhatalo c , M. Burnley d a
Chelsea School Research Centre, University of Brighton, Gaudick road, BN20 7SP Eastbourne, United Kingdom b Faculty of Sports and Physical Education Sciences, University of Lille-2, Lille, France c School of Sport and Health Sciences, University of Exeter, United Kingdom d Department of Sport and Exercise Science, Aberystwyth University, United Kingdom Received 22 January 2007; accepted 23 June 2007 Available online 24 June 2008
Abstract Aims. – Determination of critical power (CP) from a single test. Current knowledge. – Recent research has been conducted on the utility of all-out exercise to identify parameters of physiological function. This has led to the development of a protocol that would provide a means of measuring CP, that is, the lower boundary for severe exercise, in a single test. Indeed, our recent findings highlight that all-out exercise of 90 s (as the “Wingate” test) are too short for CP to be attained at the end of the exercise while the end power of a 3-min test has been shown to equal CP. The present review presents the methodological considerations to address prior to prolonged all-out exercise testing on cycle ergometers. Prospects. – We conclude by considering the possible applications of our findings to sports performance and the directions for future research in this area. © 2008 Elsevier Masson SAS. All rights reserved. Résumé Objectifs. – Évaluer la puissance critique à l’aide d’un test unique. Actualités. – Plusieurs travaux de recherche ont été conduits sur l’utilité d’un test maximal dans l’identification d’indices physiologiques fonctionnels. Ces travaux ont permis d’établir un protocole permettant de mesurer la puissance critique ou limite inférieure des intensités sévères, à partir de la réalisation d’un seul test. Nos récents résultats mettent en évidence qu’un test maximal de 90 secondes de type « Wingate » est trop court pour permettre l’atteinte de puissance critique en fin d’exercice, alors que la puissance de fin d’exercice, lorsqu’elle s’étend jusqu’à trois minutes, équivaut à la puissance critique. Dans cette revue de littérature, nous présentons les points méthodologiques à considérer lors de la mise en application de ce type de test d’effort. Perspectives. – Nous terminons en proposant des applications possibles de nos recherches dans le domaine pratique et proposons de nouvelles perspectives de recherche. © 2008 Elsevier Masson SAS. All rights reserved. Keywords: Critical power; End-power test; All-out exercise Mots clés : Puissance critique ; Puissance de fin d’exercice ; Test Wingate
1. Introduction
夽 ∗
Présentée au colloque « Puissance critique » Lille, 22 et 23 juin 2007. Corresponding author. E-mail address: [email protected] (J. Dekerle).
0765-1597/$ – see front matter © 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.scispo.2007.06.015
It is reasonably well established that the intensity of exercise can be described in terms of “domains”. Exercise performed strictly within any one of these domains results in characteristic physiological response profiles [10] and the tolerable duration of exercise is predictable when these domains are taken into account. Therefore, the measurement of the boundary between
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each exercise intensity domain is fundamental for optimizing training designs. The lactate threshold has been convincingly demonstrated to demarcate the moderate and heavy intensity domains [2], while critical power (CP) has been suggested to demarcate the heavy and severe intensity domains [42]. Incremental exercise provides the means to measure the lactate threshold and the maximal oxy˙ 2max ), but attempts to use this form of testing to gen uptake (VO identify the boundary between heavy and severe intensity exercise have been either unsuccessful [9] or, from a physiological standpoint, unconvincing [12]. Because the determination of CP requires repeated bouts of exercise with considerable recovery periods between them [23], a single-test determination of CP would be of great practical utility. In our laboratories, the utility of all-out exercise to identify parameters of physiological function has been a major research focus and this has recently led to a protocol that would provide a means of measuring CP in a single test. In the present review, we will address these recent findings and also highlight the methodological considerations required for prolonged all-out exercise testing. We conclude by considering the possible applications of our findings to sports performance and the directions for future research in this area. 2. Applying the CP concept to all-out exercise 2.1. Origin of the CP concept In 1960, a first simple two-parameter model was proposed by Scherrer and Monod [45] to characterize the work of a single local muscle pushed to exhaustion. Participants sustained several constant load tests up to exhaustion and a linear relationship was found between work (W) and time to exhaustion (t) (Eq. (1); Panel B, Fig. 1). The y-intercept was associated to a reserve of work (W ) the authors showed measurable under occlusion. The slope, originally named “threshold of local fatigue” and then “critical power”, was defined as the “maximum rate of reconstitution of the energetic potential of muscular contraction”. The numerous post hoc interpretations of the slope and the y-intercept of the W-t relationships these last 50 years have permitted a better understanding of their physiological meanings although the original definitions of Scherrer and Monod (1960) were far from erroneous.
Several reviews address issues and provide guidelines for determining CP on cycling ergometers [16,23]. Three to five tests have to be performed up to exhaustion, their duration ranging from 2 to 15 min. Subjects can be asked to race over time (the dependent variable being the work rate) or to maintain a given preset power output to exhaustion (time is here the dependent variable). The modelling of the overall power output profile will provide an estimation of CP (Fig. 1). 2.2. Physiological meaning of CP To better understand the physiological meaning of these two parameters, it might be worth considering one of its equivalent models, the hyperbolic P-t relationship. Indeed, CP is also represented by the asymptote of the P-t relationship (Panel A, Fig. 1) and is therefore mathematically defined as the power that can be maintained indefinitely (Fig. 1, Panel A). Accordingly, it was firstly thought that CP was sustainable for a “very long” period of time [18,39]. However, continued increases in blood lactate concentration, oxygen uptake and other physiological parameters (rather than the expected steady-state behaviour) have been observed during trials performed on ergometer at CP and exhaustion times ranging from 18 to 60 min have been recorded [6,28,35]. Moreover, CP has been shown to be higher than the maximal power maintainable without a substantial increase in blood lactate concentration [12,43]. The first belief that CP was sustainable for a very long period of time was a misinterpretation of its mathematical and not physiological definition. We would argue that “indefinite” (not “infinite”) represents the correct term to describe the tolerable duration of exercise at or below CP, since the power–duration relationship “cannot be used to define” the duration of exercise under these conditions. In contrast, the assertion that the tolerable duration of exercise “should be infinite” at CP is clearly at odds with common knowledge. Recently, a few studies attempted to affine the definition of CP by investigating the ˙ 2max can be attained [24,25]. It intensity domains at which VO was demonstrated that CP represented the highest intensity that ˙ 2max , is sustainable for a prolonged duration without eliciting VO that is, the lower boundary for severe exercise [17]. Accordingly, ˙ 2max , despite a some authors observed a nonattainment of VO ˙ 2 slow component during exercise performed at CP [6,42]. VO More recently, the metabolic responses to exercise above and
Fig. 1. Illustration of three different, but equivalent representations of the two-parameter model.
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below CP have been described using 31 P magnetic resonance spectroscopy. Jones et al. [51] demonstrated that work rates below CP resulted in the stabilisation of muscle phosphorylcreatine (PCr), pH and inorganic phosphate (Pi), whereas above CP, PCr declined until exhaustion ensured. Importantly, this PCr response would, during whole body exercise, be expected to be ˙ 2 with time until VO ˙ 2max mirrored by a continued increase in VO is attained, consistent with the above definition. 2.3. Physiological meaning of anaerobic work capacity That W represents an “anaerobic” capacity for work has been inferred by its lack of response to ischemia, hypoxia and hyperoxia [39], but its decrease in response to muscle glycogen depletion [38] and its increase in response to high-intensity training in untrained subjects [31] and creatine monohydrate supplementation [37]. It is also well correlated with numerous surrogate indices of anaerobic work capacity, such as the maximal accumulated oxygen deficit (MAOD; [36]) or the work performed during predominantly anaerobic exercises [13,22,26,30,46]. Heubert et al. [52] recently demonstrated an effect of a 7-s sprint postperformance test on the y-intercept of the P-t relationship decrease by 30 to 40%, while the slope was unaffected. The second parameter of the CP concept is mathematically defined as a finite reserve of energy store available preexercise [45]. Since the “notion” of anaerobic capacity is a theoretical construct itself [21], its measurement in unit of work is fraught with measurement errors. Therefore, the investigation of the nature of the second parameter of the CP concept remains difficult. However, there is some scientific evidence of its anaerobic nature. For clarity in the presentation, and for consistency with previous work, this second parameter will be abbreviated W . 2.4. Application of the CP concept to all-out exercise It has been suggested that the CP concept can be used to estimate the aerobic and anaerobic energetic contribution to any exercise performed up to exhaustion and of sufficient duration ˙ 2max to be attained [16]. It indeed assumes that the total for VO work done during an exhaustive exercise performed within the severe intensity domain (Fig. 1, Panel B, see Eq. (1)) is equal to the sum of a fixed capacity of anaerobic work (W ) and the work derived from aerobic metabolism solicited at its maximum (CP × t). The research work, recently conducted within our laboratories on the use of all-out test as a means of measuring CP, is based on the assumption that the CP concept is applicable to all-out exercise. During the early part of an all-out effort, W would be highly taxed to enable peak power to be developed in the first couple of seconds. The rapid utilisation of PCr (first few seconds) and glycolytic flux enable a very high rate of ATP resynthesis. The work rate would peak and then systematically decrease, partly due to the decline in the rate of ATP resynthesis from both substrates. The decrement would become less dramatic with time as the substrate oxidation would make the most significant, if not the main contribution to the ATP production [34].
Fig. 2. Schematic of the decrement of work rate during an all-out test up to the attainment of critical power (W , the anaerobic work capacity).
According to the CP concept, the continuous taxation of W during the exercise should lead to its total exhaustion, the endpower output being then equal to CP. The third equivalent of the W-t relationship (Fig. 1; Panel C) could be introduced to support the demonstration. Because power output is a function of the inverse of time (1/t), with CP and W being respectively the y-intercept and the slope of the relationship, when W is finally fully utilised (and equal to zero), according to the CP concept, the remaining power that is developed at the end of the exhaustive all-out test, should equal to CP (Eq. (1)). P = CP + W /t = CP + 0/t = CP
(1)
It is interesting to notice that the shape of a power-output profile obtained from the performance of an all-out exercise, such as the traditional 30-s Wingate test is very similar to the hyperbolic P-t relationship the CP concept is based on (Fig. 2). Crucially, however, the extrapolation of the power-output profile from a 30 s all-out test cannot be used to predict the power output at the conclusion of the fatigue process. Thus, the Wingate-power profile could support a variety of descriptions, ranging from the attainment of a wholly aerobic-power output (i.e., associated ˙ 2max ; [11]) to a continued fall to exhaustion. Our predicwith VO tion, however, is that the power output would ultimately attain the CP [5,7,47]. 3. All-out test – methodological considerations 3.1. Type of cycle ergometer Mechanically-braked cycle ergometers (such as Monarks; Monark Exercise AB, Sweden) are widely and traditionally used for maximal all-out test, such as the 30-s Wingate test [29]. The resistance or load to be applied against the flywheel is based on the individual body mass while considering that the optimal resistance for maximising power output varies depending on gender, age and fitness characteristics of the individual [29]. After warming up, the subject is instructed to pedal as rapidly as possible against zero resistance (in reality this is the resistance offered by flywheel inertia, the moving limbs and frictional components of the drive chain). The braking force is
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then applied as quickly as possible, with simultaneous activation of the timing process. After the load is applied, the subject continues to pedal, remaining in the seated position, as hard and fast as possible for the preset period of time (traditionally 30 s). Flywheel revolutions (or cadence) are counted (usually over intervals of 1 to 5 s) and the resistance being known, the rate of work developed throughout the test can be subsequently calculated. The Schoberer Rad Messtechnik (SRM) training system (science model powermeter, power control and computer software) provides a mean of recording power output at the crank. The cranks – it is equipped of indeed – enable the torque to be measured in the chain ring with either two, four or eight (previously 20) strain gauges, depending on the model. Torque and angular velocity data are transmitted by induction from the crank to a unit on the handlebar that converts the data to power (see [1] for more details). The SRM system has been shown to provide a valid and reliable measure of power when compared with a Monark cycle ergometer [32]. The stationary SRM ergometer enables all-out test to be run under an isokinetic mode. A cadence is imposed and controlled during the test and therefore, needs to be preset [33]. Thirty seconds before the start of the test, the subject is introduced to pedal at a slightly higher cadence (preset value + 3–5 rpm). A countdown of the last 5 s preceding the start of the all-out effort will enable the subject to push as hard as possible from the first second to the end of the test. Torque data will be measured and power calculated accordingly. Controlling the cadence during the all-out test can enriched a research design (i.e. control of the frequency of muscle contraction; consistency in the range of cadence used across a set of tests; maximisation of the total-work rate [33]). 3.2. Reliability A test cannot be considered valid if it is not reliable. Random or systematic errors in the measurement of an all-out performance can come from the cycle ergometer in use (see [41] for more details) as well as the testing itself [27]. The degree of reliability of the traditional 30-s Wingate test, performed on mechanically-braked cycle ergometers, has been widely investigated [29], while the isokinetic mode has not been such a matter of interest. We addressed this issue by looking at the reproducitibility of the power-output profile of a 90-s all-out cycling test [15]. We found peak power (1 s) to be variable between two tests evidenced by a systematic bias from test 1 to test 2 (+ 6%) and a random error of 15%. A heteroscedastic error in this measurement with higher within-subjects differences for subjects of higher peak-power values was also depicted. The higher sampling rate and therefore, higher sensitivity of measurement, could have led to the conclusion that isokinetic all-out tests are not as robust in examining peak power as previously demonstrated on friction-braked ergometers [1]. We noted that when expressed as a 5-s average, peak power was then more reliable (random error decreased to 4.6% compared to 15% with a 1-s average).
Fig. 3. Power output profiles of two subjects of similar mean powers, but with different peak powers (PP1, peak power of subject 1; PP2, peak power of subject 2) and different end powers (EP1, end power of subject 1; EP2, end power of subject 2).
The mean power over the 90 s of the test was found to be extremely robust as previously reported [27], although the test–retest variability in this measure was shown to increase with increasing values. The heteroscedastic error detected could be likened to those detected for peak power. As opposed to peak power and mean power, end power (last 10 s) did not present any heteroscedastic error in the measurement. Its systematic bias was the smallest one compared with those of the three other variables (+ 1.8%) and the random error was only equal to 9.7%. Finally, low intra-individual (a 7.6% random error) of the fatigue index was observed (64 ± 8% and 65 ± 9% for test 1 and 2, respectively). Ratio limits of agreement suggested that a repeated measurement might be expected in 95% of cases to be between 0.92 to 1.21 times the initial peak power measurement and 0.97 to 1.07 times the initial mean power measurement. The 95% limits of agreement for end power and fatigue index were 1.8 ± 9.7% and 2 ± 7.6% of the mean, respectively. It was concluded that the 90-s all-out test would be reliable for given aspects of the physiological profile, with the exception of peak power. Fig. 3 exemplifies the power-output profile of two different subjects. Peak power, mean power over the first 30, 60, and 90 s of exercise and end power (last 30 s of exercise) were also found to be reliable in children [49]. 3.3. Effects of cadence It has long been known that altering movement frequency can profoundly influence the mechanical and physiological responses to exercise. All-out tests are particularly susceptible to the influence of cadence because they are often utilized to measure divergent physiological parameters. The Wingate test is a prime example, wherein a great deal of effort has been made to
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“optimize” the Wingate protocol. In so doing, the braking force required to achieve the highest peak-power output is established and then applied during the test (usually considerably higher than the “standard” 7.5% of bodymass). However, as the test progresses, the flywheel resistance can place the subject at a considerable disadvantage later in the test. In other words, the resistance may well be “optimal” for the attainment of a peakpower output, but it may be suboptimal for all other measured parameters. This is due to the power–velocity relationship of the musculature involved in cycling. The rapid decline in power (and cadence) results the subject’s cadence very rapidly deviating from optimal as the test progresses and as a result the subject “underperforms” the test. This is a serious concern for all-out exercise and, because the range of power output is so large for these kinds of tests, the solution is not straightforward. Choosing isokinetic testing eliminates the change in cadence as the test progresses, but because the power–velocity relationship is known to change as fatigue ensues [44], the cadence is once again only fleetingly optimal. A fixed resistance and variable cadence may, as discussed above, not be truly optimal at any point in the test, but may at least be close to optimal. Our research groups have adopted both approaches due for the most part to the ergometer available for testing (Lode versus SRM). The 3-min all-out test has to date been performed using the Lode Excalibur Sport ergometer and for sprint work, this ergometer is placed in its cadence dependant mode (where power = linear factor × cadence2 ). In designing the test, we were most interested in the power at the end of the test and not the beginning and so we purposefully adopted a strategy of setting the linear factor in such a way that if the subject’s preferred cadence (usually 80 to 90 rpm) was attained, this would happen ˙ 2max at a power output equal to 50% (that is, GET + [0.5 × VO − GET]). One immediate concern was that the resistance set is entirely dependent on what the subject chooses as their preferred cadence. Consequently, we designed a study to investigate the influence of the adoption of different preferred cadences to determine if the power profile of the test and the parameters derived would be altered. Our results showed a small reduction (∼ 9 W) in the end-test power (EP) output when cadence was increased (by 10 rpm above preferred), but not when a similar reduction from the preferred cadence was adopted [48]. However, both the peak-power output and the amount of work done above the EP output were systematically affected: higher cadences reduced these parameters, whereas lower cadences increased them. This, we suggested, could be explained by the power–velocity relationship, because the peak cadence achieved in the high cadence trial was 155 ± 12 rpm and would, therefore, have placed the subjects on the descending limb of the relationship. At the end of the test, when the fatigue processes had reduced and flattened the parabolic power–velocity relationship, the influence of cadence manipulation on power output would have been much smaller, although still evident for the highest cadence studied [48]. Interestingly, these findings suggest that all-out exercise can provide insight into the power–velocity relationship as well as the power–duration relationship (see below).
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4. Recent findings 4.1. The 90-s test – data showing the end-test power to be higher than CP The contribution of both the anaerobic and aerobic pathways to the total-energy release during the performance of an all-out test remains under scrutiny [3,4,40]. It has recently been estimated that 40 to 50 s would be the time required for endurance-trained cyclists to utilize the totality of their anaerobic capacity during an all-out test performed in normoxia [8]. Accordingly, previous findings demonstrated that in predominantly aerobically-trained subjects, the oxygen deficit is smaller during 45-s when compared to 60- and 90-s, but tends to plateau after 60 s of all-out exercise performed on an air-braked ergometer [50]. These findings were later confirmed in a sample of active male [20]. Evaluation of the 90-s test further indicated that maximal or near-maximal (98%) anaerobic-energy release was achieved in 60 s. Based on previous findings, we thought that 90 s would be of sufficient duration to completely exhaust the W , and for CP to be attained at the end of the all-out test (Fig. 2). We designed a study to establish the validity of the 90-s all-out test for the determination of both maximal and submaximal indices of aerobic fitness. We hypothesized that the peak-oxygen uptake at ˙ 2max attained in a ramp the end of the 90-s trial and the VO exercise would be equal. Furthermore, we hypothesized that the power output attained at the end of the all-out test would equate to the individual’s CP [5]. Sixteen subjects (12 men and four women; mean ± S.D.; age: 30.4 ± 6.1 years; weight: ˙ 2max : 3.9 ± 0.7 L−1 ) firstly completed a ramp 69.6 ± 9.9 kg; VO ˙ 2max (5 W/min). Secondly, test to exhaustion to determine VO CP was determined from three separate constant-load tests to exhaustion (exhaustion times ranging from 2 to 15 min). Finally, each subject underwent two separate 90-s all-out efforts. ˙ 2max was not attained at the end of a It was found that VO ˙ 2max ) and even under the condi90-s all-out test (88% of VO tions of considerable fatigue at the end of this test, the final power output was in excess of the individual’s CP (equating ˙ 2max and percentage of CP; Fig. 4). Therefore, 94% of P – VO our hypothesis that there would be agreement between our mark˙ 2max ers of maximal and submaximal aerobic capacity (the VO and CP of the 90-s all-out test, respectively) determined independently and together within a single 90-s all-out test was not supported. A high correlation was obtained between end power and CP (R = 0.86), highlighting that these two variables could be related. The power output during the 90-s test declined below CP for two of the 16 subjects (− 30 and − 34 W). For three other subjects, the difference between end power and CP was lower than 8 W (representing 3% of CP). It was hypothesized that a test of longer duration would allow CP to be attained. 4.2. The 3-min all-out test: measuring CP in a single test Although the 90 s all-out test end-power appears to overestimate CP, it did provide additional evidence that such prolonged all-out exercise is a reliable exercise test. Moreover, the power
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Fig. 4. Critical power (± 95% confidence interval) and end-power values for each participant.
output attained at the end of the test was certainly below that ˙ 2max during an exhaustive ramp test [5,14]. required to attain VO Our investigations in Aberystwyth led to the adoption of a 3-min all-out cycling test against a fixed resistance in an attempt to determine CP. Our first experimental study provided promising initial evidence that the boundary between heavy- and severeintensity exercise may indeed be estimated by all-out exercise [7]. In this work, we determined the 3-min test end-power
Fig. 6. Agreement between the 3-min all-out test end-power and CP from 10 subjects [47]. Dashed line represents the line of identity.
˙ 2 and blood [lactate] responses to and then measured the VO exercise performed 15 W above (presumably severe) and 15 W below (presumably heavy) the EP. Nine of the 11 subjects tested completed 30 min of exercise 15 W below the EP output and ˙ 2 and blood [lactate] seven subjects did so with steady state VO responses. In contrast, none of the subjects completed 30 min ˙ 2 and blood [lacof exercise 15 W above the EP, and the VO tate] responses indicated that all subjects were exercising in the severe-intensity domain [7]. We concluded that the EP is likely to be equivalent to the CP, but that further work was necessary to compare these parameters directly. In a subsequent paper, we tested the hypothesis that the CP and the EP measured in a 3-min test would be equivalent [47]. To do this, we defined the power duration relationship in 10 subjects using five predicting trials of exhaustive exercise and compared the CP and W to the EP and the “work done above end-test power” (WEP), respectively. As shown in Figs. 5 and 6, there was a very close agreement between the parameters estimated “traditionally” from five predicting trials and those estimated from the 3-min all-out test. These results seem so unambiguous that we remain somewhat surprised that in spite of the fact that Monod and Scherrer (1965) explicitly stated that CP cannot be measured during a single bout of exercise, it took more than 40 years for anybody to ask “is that so?”! More importantly, the answer to that question is a resounding “no!” and thus, the 3-min all-out test provides a potentially very efficient and widely applicable means of determining crucial parameters of the physiology of exercise that are often overlooked (or at least not measured) by most of the research community. 5. Applications and future directions
Fig. 5. The CP estimated from the 1/time model (top panel) and the power profile during the 3-min all-out test (bottom panel) in a representative subject. Note the close agreement between the parameter estimates derived from each method.
The analysis of a power-output profile from the performance of an all-out test was originally proposed to assess the anaerobic power and capacity of an individual [29]. Recent studies conducted in our laboratories led to the conclusion that maximal and submaximal indices of aerobic fitness can also be derived from such a performance. Indeed, the sole perfor-
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˙ 2max and CP to be mance of a 3-min all-out test allows VO attained. This should be considered when profiling athletes in laboratories for consultancy or research purposes. Moreover, the several studies recently conducted on the 90-s and 3-min all-out tests offer a new insight into the energetic contribution to all-out effort, using our current understanding of the CP concept. Their outcomes could directly affect training and coaching interventions in specific sports, such as track cycling where power-output profiles are close to those of all-out exercise [19]. Our two laboratories have recently investigated the effect of two different interventions on both CP and the end power of an all-out test. It was hypothesised that the effects of moderate normobaric hypoxia and aerobic training would be of similar magnitude on these two variables, if the two were causally linked. We should soon publish the results of these two studies. We have recently conducted a study on the power-output profiles of paediatric populations (CP concept and 90-s all-out test) and are hoping publishing the main findings in the coming months. These recent findings should lead to a better understanding of exercise tolerance across environmental conditions, levels of fitness and adult versus children. 6. Conclusions Critical power represents the highest intensity that is sustain˙ 2max , that is, able for a prolonged duration without eliciting VO the lower boundary for severe exercise and its measurement is fundamental for optimizing training designs. It is traditionally determined from the performance of several maximal constantload efforts. Recent studies, conducted within our laboratories, demonstrated that the performance of a single all-out test of sufficient duration to totally exhaust the anaerobic work capacity enables CP to be accurately measured. “Linear” (isotonic) as well as isokinetic modes can be used to obtain the poweroutput profile of an individual’s all-out effort and the choice of one of the two modes will depend on the purpose of the testing and cycle ergometer availabilities. It is hoped that the recommendations mentioned in the present article will well guide any researcher or laboratory instructor willing to use these all-out tests for individual profiling. Further publications should follow the present review on the use of all-out exercise in measuring CP. References [1] Balmer J, Bird S, Davison RC, Doherty M, Smith P. Mechanically braked Wingate powers: agreement between SRM, corrected and conventional methods of measurement. J Sports Sci 2004;22(Suppl. 7):661. [2] Barstow TJ, Casaburi R, Wasserman K. O2 uptake kinetics and the O2 deficit as related to exercise intensity and blood lactate. J Appl Physiol 1993;75(Suppl. 2):755. [3] Beneke R, Hutler M, Leithauser RM. Anaerobic performance and metabolism in boys and male adolescents. Eur J Appl Physiol 2007; 101(Suppl 6):671. [4] Beneke R, Pollmann C, Bleif I, Leithauser RM, Hutler M. How anaerobic is the Wingate anaerobic test for humans? Eur J Appl Physiol 2002;87(Suppl. 4–5):388.
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