Robustness of a 3 min all-out cycling test to manipulations of power profile and cadence in humans

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1 Exp Physiol 93.3 pp Experimental Physiology Robustness of a 3 min all-out cycling test to manipulations of power profile and cadence in humans Anni Vanhatalo 1, Jonathan H. Doust 2 and Mark Burnley 1 1 Department of Sport and Exercise Science, University of Wales, Aberystwyth, Ceredigion SY23 3FD, UK 2 Chelsea School Research Centre, University of Brighton, Eastbourne, East Sussex BN20 7SP, UK The purpose of this study was to assess whether end-test power output (EP, synonymous with critical power ) and the work done above EP (WEP) during a 3 min all-out cycling test against a fixed resistance were affected by the manipulation of cadence or pacing. Nine subjects performed a ramp test followed, in random order, by three cadence trials (in which flywheel resistance was manipulated to achieve end-test cadences which varied by 20 r.p.m.) and two pacing trials (30 s at 100 or 130% of maximal ramp test power, followed by 2.5 min all-out effort against standard resistance). End-test power output was calculated as the mean power output over the final 30 s and the WEP as the power time integral over 180 s for each trial. End-test power output was unaffected by reducing cadence below that of the standard test but was reduced by 10 W on the adoption of a higher cadence [244 ± 41 W for high cadence (at an end-test cadence of 95 ± 7 r.p.m.), 254 ± 40 W for the standard test (at 88 ± 6 r.p.m.) and 251 ± 38 W for low cadence (at 77 ± 5 r.p.m.)]. Pacing over the initial 30 s of the test had no effect on the EP or WEP estimates in comparison with the standard trial. The WEP was significantly higher in the low cadence trial (16.2 ± 4.4 kj) and lower in the high cadence trial (12.9 ± 3.6 kj) than in the standard test (14.2 ± 3.7 kj). Thus, EP is robust to the manipulation of power profile but is reduced by adopting cadences higher than standard. While the WEP is robust to initial pacing applied, it is sensitive to even relatively minor changes in cadence. (Received 10 August 2007; accepted after revision 17 October 2007; first published online 19 October 2007) Corresponding author M. Burnley: Department of Sport and Exercise Science, Carwyn James Building, University of Wales, Aberystwyth, Ceredigion SY23 3FD, UK. mhb@aber.ac.uk We have recently provided evidence that a 3 min all-out cycling test can be used to establish peak oxygen uptake ( V O2 peak; Burnley et al. 2006) and, by measuring the power output in the last 30 s of the test, critical power (Vanhatalo et al. 2007). These results suggest that all-out exercise can be used to identify the boundary between what have been termed heavy and severe intensity exercise (Gaesser & Poole, 1996; Jones & Poole, 2005), which previously required several exercise tests to define from the power duration relationship (Monod & Scherrer, 1965; Moritani et al. 1981; Poole et al. 1988) or the maximal lactate steady-state protocol (MLSS; Beneke & von Duvillard, 1996). The 3 min all-out test is therefore a promising and economical method of establishing important aerobic parameters. However, it is not known whether the 3 min all-out test parameters are robust to manipulations of the test protocol. The rationale for the 3 min all-out test is based on the power duration relationship and has been described in detail previously (Vanhatalo et al. 2007). Briefly, if subjects exercise maximally against a constant resistance, they reach an asymptote in power output (the end-power, EP) after min, which is equivalent to critical power (CP), with the amount of work done above EP (the WEP) providing an estimate of the curvature constant of the power duration relationship, denoted W. Our previous work has demonstrated that the W is fully utilized during 3 min of all-out cycling (Vanhatalo et al. 2007), and Fukuba et al. (2003) showed that stepwise variation of constant power outputs during an exhaustive bout of exercise resulted in work done above CP being equal to the independently estimated W. Despite this early promise, we have previously expressed concerns that although the EP seems to faithfully represent CP, the WEP may be DOI: /expphysiol

2 384 A. Vanhatalo and others Exp Physiol 93.3 pp sensitive to the test protocol (Vanhatalo et al. 2007). If, however, the WEP represents the same construct as W, the magnitude of the WEP should also remain the same when the power profile of a 3 min test is manipulated (cf. Fukuba et al. 2003). The oxygen cost of generating a given constant power output increases with cadence for cycling exercise (MacIntosh et al. 2000; Barker et al. 2006). It is conceivable that cadence may also influence the power duration parameters estimated from a single bout of all-out cycling against fixed resistance, where a wide range of pedal rates are generated throughout the test, according to the subject s maximal effort. Previously, we have standardized the 3 min all-out test protocol by performing it on an electronically braked cycle ergometer (Lode Excalibur Sport, Groningen, The Netherlands) against a fixed resistance, which has been determined so that the power output equal to the gas exchange threshold (GET) plus 50% of the interval between GET and V O2 peak (i.e. 50% ) is attained at subjects preferred cadence (80 or 90 r.p.m. in most cases). It is important to note that a seemingly small change in preferred cadence used to calculate the flywheel resistance for the test results in a disproportionate change in the resistance setting (resistance = power/r.p.m. 2 ). Consequently, the selection of different preferred cadences could potentially have a considerable effect on the pedalling rate and power generation during 3 min of all-out cycling. From a practical viewpoint, it would therefore be useful to establish the robustness of the 3 min all-out test to the changes in pedal cadence within a conservative range of ±10 r.p.m. which could be attributed to the subjective selection of preferred cadence. The purpose of this study was to test the hypotheses that: (1) the EP and the WEP should remain constant when the power output in the first 30 s of a 3 min all-out test is varied; and (2) the EP and WEP parameters would remain unaffected when three different flywheel resistances are adopted to manipulate the end-test cadence over a 20 r.p.m. range (representing the likely range of subjectively selected preferred cadences ). Methods Subjects Nine subjects (8 male) volunteered for the study (mean ± s.d. age 30 ± 4 years; body mass 73.1 ± 12.1 kg; and height 1.78 ± 0.06 m), including road cyclists (n = 4), distance runners (n = 2) and those in general fitness training (n = 3). Prior to testing, subjects were informed of the protocol and risks and gave written consent to participate. All procedures were approved by the ethics committee of the University of Wales, Aberystwyth and were conducted in accordance with the Declaration of Helsinki. Subjects were instructed to be adequately hydrated and not to have consumed alcohol for 24 h, and food or caffeine for 3 h before each test. Experimental design The protocol required seven visits to the laboratory. Tests were separated by a minimum of 24 h rest, and all testing was completed within 3 weeks. The subjects performed an incremental ramp protocol at the ramp rate of 30 W min 1 for the assessment of V O2 peak and the gas exchange threshold (GET), and one 3 min all-out familiarization trial. The following five tests were performed in a random order. The tests included one standard 3 min all-out test, two 3 min all-out tests performed against different fixed resistances (cadence trials) and two 3 min tests where the power output over the initial 30 s was kept constant at either 100 or 130% of the maximal ramp test power followed by a 2.5 min all-out effort (pacing trials). Determination of peak oxygen uptake and GET All exercise testing was conducted using an electrically braked cycle ergometer (Lode Excalibur Sport, Groningen, The Netherlands). The ergometer seat and handlebars were adjusted for comfort, with cyclists own pedals fitted if required and settings replicated for subsequent tests. The ramp protocol consisted of 3 min of unloaded baseline pedalling, followed by a ramp increase in power output of 30 W min 1 until volitional exhaustion. Subjects were instructed to maintain their preferred cadence (80 r.p.m. n = 3; 90 r.p.m. n = 6) for as long as possible. The test was terminated when the pedal rate fell more than 10 r.p.m. below the chosen cadence for more than 10 s, despite strong verbal encouragement. The V O2 peak was determined as the highest average oxygen uptake ( V O2 ) over a 30 s period. Data were reduced to 10 s averages for the estimation of GET using the V-slope method (Beaver et al. 1986). Standard 3 min all-out test and cadence trials Subjects warmed up for 5 min at 100 W, followed by 5 min rest, and each test began with 3 min of unloaded baseline pedalling. For the all-out phase, the ergometer was set on the cadence dependent mode where: Power output = LF cadence 2 where LF represents the linear factor (flywheel resistance). The resistances for the standard test and the cadence trials were calculated as follows: Standard test: LF = 50% /(preferred cadence) 2

3 Exp Physiol 93.3 pp Cadence and pacing in all-out cycling 385 Low cadence: LF = 50% / (preferred cadence 10 r.p.m.) 2 High cadence: LF = 50% / (preferred cadence + 10 r.p.m.) 2 where 50% is a power output set at GET +50% of the interval between V O2 peak and GET. Therefore, the 50% power output would be attained on reaching the preferred cadence during the standard trial, on reaching a cadence 10 r.p.m. below preferred cadence during the low cadence trial and 10 r.p.m. above preferred cadence during the high cadence trial. Preferred cadence was the same as applied previously in the incremental ramp protocol. Subjects were instructed to accelerate to 120 r.p.m. over the last 5 s of the unloaded baseline pedalling and to elicit a maximal sprint from the start of the test. Strong verbal encouragement was provided throughout the test, but the subjects were not informed of the elapsed time in attempt to prevent pacing. For an all-out effort, subjects were instructed to maintain the cadence as high as possible at all times throughout the test. The V O2 peak was calculated as the highest 30 s average achieved during the test, and blood [lactate] was measured at rest prior to the test and immediately following its completion as described below. Manipulation of power profile Subjects performed two trials which consisted of a 30 s constant work rate phase and a 2.5 min all-out phase, in order to test the hypothesis that the 3-min test parameters would remain robust to changes in the power profile. Before each test subjects warmed up for 5 min at 100 W, followed by 5 min rest. The test began with 3 min of unloaded baseline pedalling, after which a constant work rate of either 100% or 130% of maximal power attained in the ramp test was imposed, using the cadence independent (hyperbolic) mode of the ergometer. After 30 s the ergometer switched to cadence dependent (linear) mode set with the standard resistance, and from this point onwards the subjects were strongly encouraged to elicit maximal effort, and to maintain the cadence as high as possible at all times throughout the reminder of the test. Subjects were aware of the time over the first 30 s of the test, after which no further information of the elapsed time was given during the all-out phase. The V O2 peak was calculated as the highest 30 s average achieved during the test, and blood [lactate] was measured at rest prior to the test and immediately following its completion as described in the Equipment subsection below. Equipment Pulmonary gas exchange was analysed breath-by-breath throughout exercise in all tests. Subjects wore a noseclip and breathed through a low dead space (90 ml), low resistance (0.75 mmhg l 1 s 1 at 15 l s 1 ) mouthpiece and impeller turbine assembly (Jaeger Triple V, Hoechberg, Germany). The inspired and expired gas volume and gas concentration signals were continuously sampled at 100 Hz, the latter using paramagnetic (O 2 ) and infrared (CO 2 ) analysers (Jaeger Oxycon Pro, Hoechberg, Germany) via a capillary line connected to the mouthpiece. These analysers were calibrated before each test with gases of known concentration, and the turbine volume transducer was calibrated using a 3 l syringe (Hans Rudolph, Kansas City, MO). The volume and concentration signals were time aligned by accounting for the delay in capillary gas transit and analyser rise time relative to the volume signal. Oxygen uptake, carbon dioxide output and minute ventilation were calculated using standard formulae (Beaver et al. 1973) and displayed breath-by-breath. Heart rate was measured every 5 s using short-range radio telemetry (Polar S610, Polar Electro Oy, Kempele, Finland). Fingertip blood ( 25 μl) was collected into capillary tubes and analysed for blood [lactate] using an automated lactate analyser (YSI Stat 2300, Yellow Springs, OH, USA), which was calibrated hourly using the manufacturer s standard (YSI 2747). Data analyses The end-test power was calculated as the average power output over the final 30 s and the WEP as the power time integral above EP over 180 s for all trials. The O 2 cost of exercise was determined for all trials using the gain ( V O2 /power output) at 15 s intervals during the test. The time courses of the individual V O2 responses were estimated by fitting a monoexponential function to the entire V O2 response (i.e. from time zero with no delay term) using iterative non-linear regression (to approximate the mean response time, MRT). This MRT was used to determine when the V O2 response was 98% complete (4 MRT; Jones & Poole, 2005), so that the O 2 cost following the attainment of a peak V O2 could be calculated. Parameter comparisons between trials were analysed using a one-way ANOVA with repeated measures. Specific differences were identified using 95% pairedsamples confidence intervals. Statistical significance was accepted at P < 0.05 level and data are presented as means ± s.d. Results The V O2 peak measured in the ramp test was 3.82 ± 0.60 l min 1, the peak power output 364 ± 49 W, and the GET 2.13 ± 0.24 l min 1 (130 ± 18 W). The pulmonary gas exchange and ventilatory data presented for the all-out trials were sampled from six

4 386 A. Vanhatalo and others Exp Physiol 93.3 pp Table 1. The mean responses (± s.d.) to the standard 3 min all-out test and the cadence and pacing trials Cadence trials Pacing trials Standard Low r.p.m. High r.p.m. 100% max. power 130% max. power V O2 peak (l min 1 ) 3.76 ± ± ± ± 0.61 ab 3.61 ± 0.61 a Total O 2 (l) 9.96 ± ± ± ± 1.49 b 9.49 ± s Gain (ml min 1 W 1 ) 9.4 ± ± ± ± ± s Gain (ml min 1 W 1 ) 10.9 ± 0.8 d 10.6 ± 1.1 d 10.6 ± 0.9 d 9.7 ± 1.6 d 10.1 ± 1.1 d Mean response time (s) 23.1 ± ± 3.3 b 23.1 ± ± 6.8 b 32.4 ± 7.4 b Peak power (W) 723 ± ± ± 122 bc 595 ± 112 b 529 ± 118 b (% max. power) (200%) (218%) (178%) (164%) (145%) Peak cadence (r.p.m.) 148 ± ± 10 b 155 ± 12 bc 135 ± 13 b 126 ± 13 b EP (W) 254 ± ± ± 41 b 249 ± ± 39 (52% ) (51% ) (48% ) (50% ) (49% ) End cadence (r.p.m.) 88 ± 6 77± 5 b 95 ± 7 bc 87 ± 6 86± 7 WEP (kj) 14.2 ± ± 4.4 b 12.9 ± 3.6 bc 14.1 ± ± 5.3 Work done (kj) 59.7 ± ± ± 6.7 bc 58.7 ± ± 8.4 Peak power and peak cadence were measured over 1 s, and EP and end cadence averaged over 30 s. For V O2 peak, total O 2 and gain, n = 6; for all other variables n = 8. a Significantly different from ramp test, P < 0.05; b significantly different from standard trial, P < 0.05; c significantly different from low r.p.m. trial, P < 0.05; and d significantly different from 90 s gain, P < Gain is V O2 / power output; max. power is maximal power attained in the ramp test; and is the interval between GET and V O2 peak. subjects. One subject did not consent to wearing the mouthpiece during the tests, and in two other instances the subjects removed the mouthpiece during the test owing to discomfort. Power profile The EP estimates derived from the 100 and 130% trials were not significantly different from that measured in the standard test (F 2,8 = 1.24, P = 0.32). In comparison to the standard trial, the WEP (F 2,8 = 3.17, P = 0.069) and the total work done (F 2,8 = 0.90, P = 0.43) were also found to be unaffected by the manipulation of the power profile over the first 30 s (Table 1). The comparison of WEP between the standard and pacing trials was associated with only a moderate power (1 β = 0.52), and therefore post hoc analyses were conducted to determine whether this result represented a type II error. The paired-samples 95% confidence limits (CL) associated with the difference between the WEP of the standard versus 100% trial ( 0.547, kj) and the standard versus 130% trial ( 3.613, kj) suggested that no such error occurred. The peak power outputs were attained at 35 s (range s) during the pacing trials and were significantly lower than the peak in the standard test (F 2,8 = 28.77, P < 0.001; Fig. 1A). The end-test cadences in the 100 and 130% trials, conducted using the standard resistance over the final 2.5 min, were not different from the standard trial (F 2,8 = 1.97, P = 0.17; Table 1). Cadence The different flywheel resistances had a significant effect on the WEP between trials (F 2,8 = 21.02, P < 0.001). Specifically, the WEP in the low cadence trial was higher (95% confidence intervals 3.29, 0.54 kj) and the WEP in the high cadence trial was lower (95% confidence limits, 0.75, 2.65 kj) than in the standard test (Table 1). There was no significant main effect between trials on the EP estimates (F 2,8 = 3.26, P = 0.065; Table 1 and Fig. 1); these results also suggested a tendency for EP to differ with pedalling cadence. The power associated with these comparisons was also moderate (1 β = 0.54), and post hoc analyses revealed that the EP in the high cadence trial was lower than in the standard test (95% CL 0.32, W; Fig. 1B). Total accumulated work was lower in the high cadence trial compared with the low cadence trial (95% CL 1.50, 0.52 kj). The manipulation of flywheel resistance resulted in significant differences between the two trials and the standard test in both peak (F 2,8 = 23.41, P < 0.001) and end-test cadences (F 2,8 = , P < 0.001; Table 1 and Fig. 1C). The peak power output, which was attained within 4 s (range 1 9 s), was highest in the low cadence trial and lowest in the high cadence trial (F 2,8 = 16.05, P < 0.001). Physiological responses The highest V O2 values measured were approximately 98, 98 and 94% of the ramp test V O2 peak for the standard, low and high cadence trials, and 92 and 94% for the 100 and 130% trials, respectively (F 4,5 = 3.38, P = 0.018). Specific differences were detected in V O2 peak between the ramp test and the 100% trial (95% CI 0.11, 0.49) and the ramp test and the 130% trial (95% CI 0.013, 0.42). The total oxygen consumed was lower during the pacing trials compared with the standard all-out test (F 2,5 = 8.19, P = 0.008; Table 1). Blood [lactate] values measured at the

5 Exp Physiol 93.3 pp Cadence and pacing in all-out cycling 387 end of exercise were 11.2 ± 1.9 (standard), 11.8 ± 1.7 (low cadence), 11.4 ± 1.8 (high cadence), 11.2 ± 1.8 (100% trial) and 10.8 ± 1.1 mm (130% trial). The V O2 response profiles for each condition are shown in Fig. 2. The MRT (time taken to attain 63% of the peak V O2 measured during the test) was significantly higher in the low cadence trial (F 2,5 = 6.22, P = 0.018) and both pacing trials (F 2,5 = 9.877, P = 0.004) than in the standard test (i.e. the V O2 kinetic response was slower). The relationship between power output and V O2 for the standard 3 min test and the 100% trial are displayed in Fig. 3. The rise in V O2 and fall in power output were reflected as an increasing gain throughout both tests. This finding was common to all trials, with the 180 s gain being significantly greater than the 90 s gain in all cases (F 1,5 = , P < 0.001; Table 1). Discussion The results of the present study confirm the first hypothesis in showing that the EP and WEP parameters were both unaffected by the manipulation of the power profile over the first 30 s of a 3 min all-out test performed against fixed resistance. In contrast to the second hypothesis, however, when the fixed resistance was manipulated to yield mean Figure 1. The power profiles of the pacing trials (A) and cadence trials (B) in comparison to the standard 3 min test in all subjects Error bars are not shown for clarity. The different work rates applied during the first 30 s of these trials resulted in marked differences in power profiles over the first s of the test (A), with no differences in the end-test power outputs. B shows a similar end-test power output during the standard test and low cadence trial, despite clear differences in cadences throughout these trials (C), whilst the high cadence trial resulted in an end-test power that was 10 W lower than the standard test. Figure 2. The pulmonary V O2 responses to the two pacing trials and a standard 3 min all-out test (n = 6) Note that the V O2 response is similar during the cadence trials (A), but that V O2 rises more rapidly during the standard trial than when the first 30 s is paced (B).

6 388 A. Vanhatalo and others Exp Physiol 93.3 pp cadences 10 r.p.m. above and below the standard, the EP was found to be significantly reduced in the high cadence trial in comparison to the standard test (by 10 W). In addition, the WEP was significantly higher in the low cadence trial and significantly reduced in the high cadence trial. Therefore, the 3 min all-out test, whilst providing an accurate estimate of the critical power under standard test conditions (Vanhatalo et al. 2007), can be sensitive to minor variations in the ergometer resistance setting. An important finding of the present study was that the work done above end-test power remained the same when different constant work rate phases were combined with an all-out phase in a 3 min cycling test performed at the standard resistance. Our previous work showed that the WEP in a standard 3 min all-out test can be used to estimate the W (Vanhatalo et al. 2007); however, it was not shown whether the magnitude of the WEP parameter would be affected by its temporal allocation during the test. It has now been demonstrated that the magnitude of the W remains the same for constant single work rate exercise (Hill, 1993; Smith & Hill, 1993; Hill & Smith, 1994; Morton & Billat, 2004); for stepwise variations of constant work rates (Fukuba et al. 2003); for incremental ramp exercise (Morton et al. 1997; Pouilly et al. 2005); and, assuming that WEP is equivalent to W, for combinations of constant work rate and all-out exercise. Despite marked differences in power outputs over the initial 30 s, the power profiles in the two pacing trials levelled out 120 s into the test to attain the same endtest power as in the standard 3 min all-out test. The power outputs of 100 and 130% of ramp test maximum were chosen in order to keep the duration of the subsequent all-out phase reasonably short, while still allowing enough time for the WEP to be completely accumulated. Approximately 69% of the WEP was accumulated over the first 30 s in the standard all-out test, compared with 43% in the 130% trial and only 24% in the 100% trial. After 90 s, 10% of the WEP remained when 100 and 130% pacing strategies were used, and only 5% when all-out strategy was applied. By the end of the test, there were no differences in Figure 3. Temporal profiles of power output, V O2 and gain during the standard 3 min test and the 100% pacing trial These trials are displayed not for comparison but to illustrate the profiles during a 3 min all-out test and a pacing trial. The top panels illustrate that V O2 rises rapidly within the first s and remains elevated thereafter, and power output falls rapidly and then more gradually as the all-out phase of the test proceeds. The resulting gain ( V O2 /power output in 15 s time bins; bottom panels) rises throughout the tests, despite V O2 increasing by < 150 ml min 1 over the final 90 s.

7 Exp Physiol 93.3 pp Cadence and pacing in all-out cycling 389 power outputs between the three trials. The total oxygen uptake over the 3 min was higher in the standard test than in the 100% pacing trial with no differences in the total mechanical work done, indicating that the aerobic contribution was greater when exercising all-out from the start of the test. This interpretation is also supported by the smaller MRT of the V O2 kinetic response in the standard test compared with the pacing trials. Although the power outputs in the pacing trials were evidently high enough to allow for the full magnitude of WEP to be accumulated, it is clear that the most time efficient strategy to accumulate the total WEP, to attain the levelling out in power profile and to reach the V O2 peak, is by maximal voluntary effort from the onset of exercise. The WEP was shown to be systematically altered by the cadence adopted during all-out exercise. In contrast, previous work using greater cadence ranges (e.g. 60 versus 120 r.p.m.) than applied in the present study has demonstrated that the conventional critical power protocol tends to yield reduced estimates of CP at high cadences while the W remains unaffected (Carnevale & Gaesser, 1991; Hill et al. 1995; McNaughton & Thomas, 1996; Barker et al. 2006). The effect of altering pedal cadence may, however, be quite different during all-out exercise. The peak power output during all-out exercise is well described as a parabolic function of cadence (Sargeant et al. 1981), due to power output being a product of the hyperbolic relationship between tangential crank force and velocity. It has been suggested that for subjects possessing approximately equal proportions of type I and II muscle fibres, the optimal cadence for peak power production in cycling is r.p.m. (Sargeant et al. 1981; Sargeant, 1994). Assuming that these findings apply to our subjects, the resistances used in the present study were suboptimal for the attainment of peak power output, because they yielded peak cadences of r.p.m. (Table 1). The low cadence trial yielded a peak cadence closest to, but still above, the optimum, whereas the standard and high cadence trials would have shifted peak cadence increasingly to the right of the optimum (i.e. on the descending limb of the parabolic power velocity relationship). Since most of the WEP is accumulated in the first 30 s of the test, it follows that WEP should decrease as the cadence is increased and therefore the peak power output is decreased. Therefore, whilst the WEP is similar in magnitude to the W parameter of the power duration relationship (Vanhatalo et al. 2007), its value is likely to be determined, in part, by the power velocity relationship, which is itself determined by the chosen flywheel resistance. The effect of fatigue on muscle power production is augmented at high contraction velocities, i.e. at versus r.p.m. (Suzuki, 1979; McCartney et al. 1983; Beelen & Sargeant, 1991; Hill et al. 1995), and therefore it may have been expected that the EP would be lowest in the high cadence trial and highest in the low cadence trial. The present study provides partial support for this proposition, in that increasing the test cadence (by reducing the ergometer resistance) reduced the EP by 10 W. This may be explained by the power velocity relationships of different fibre types (Beelen & Sargeant, 1991) and/or differences in the internal power output. In respect of the latter, Barker et al. (2006) suggested that the lower CP they observed at 100 versus 60 r.p.m. may have been due, in part, to the higher internal power requirements (to move the legs) at higher contraction frequencies (Ferguson et al. 2000). In the high cadence trial, therefore, more of the power-generating capacity would have been used to satisfy the internal power requirements than in the standard and low cadence trials. It is important to stress, however, that the reduction in EP observed in the high cadence trial is relatively small considering that the test retest 95% confidence limits of the 3 min all-out test have been reported to be 7 W (Burnley et al. 2006). The initial s of all-out cycling exercise undoubtedly requires the maximal activation of all muscle fibre types to achieve peak power output (Sargeant et al. 1981; McCartney et al. 1983; Davies & Sandstrom, 1989). This, in turn, will result in extremely high rates of phosphorylcreatine hydrolysis that will drive V O2 upwards (Whipp & Mahler, 1980), resulting in the rapid attainment of V O2 peak, as demonstrated for the standard trial in the present study. It is also well established that the most powerful fibres will also fatigue rapidly (Beelen & Sargeant, 1991), reducing their external power contribution substantially or even completely (McCartney et al. 1983). These fibres will continue to consume O 2 to restore ionic and metabolite homeostasis whilst less fatigued fibres continue to produce power and also consume O 2. The combined O 2 demand from both fatigued fibres and non-fatigued fibres, in addition to the O 2 cost of support processes outside the skeletal muscle, probably serve to maintain whole-body V O2 close to its peak as power output continues to fall. These events would be reflected as an increasing gain during the prolonged all-out test and the attainment of an end-test power resulting from the power production of a population of fatigue-resistant fibres (predominantly, though probably not exclusively, type I fibres; Sargeant, 1994). Though speculative, this may also explain why the EP was reduced in the high cadence trial, in that cadences of r.p.m. recorded over the final 30 s of the high cadence trial may have placed the type I fibres further along the descending limb of their power velocity relationship. In contrast, the end-test cadences in the standard and low cadence trials (70 90 r.p.m.) may have placed those same fibres closer to the apex of the parabolic relationship. In summary, it has been shown that the EP and WEP parameters were unaffected by variation of work rates over the initial 30 s of a 3 min all-out test. The present investigation has further demonstrated that while the EP

8 390 A. Vanhatalo and others Exp Physiol 93.3 pp was not altered when the mean test cadence was reduced by 10 r.p.m. below standard, increasing the mean cadence by 10 r.p.m. resulted in a significantly lower EP than that measured in the standard test. The WEP was shown to be significantly reduced at high cadences and enhanced at low cadences. Therefore, the work done above the EP, whilst robust to manipulations of the power profile early in the test, is sensitive to alterations in pedal cadence. The 3 min all-out cycling test provides a robust EP (which has been shown to provide an accurate estimate of critical power; Vanhatalo et al. 2007) if the ergometer resistance is set to achieve an end-test cadence equal to or slightly below the subject s preferred cadence. References Barker T, Poole DC, Noble LM & Barstow TJ (2006). Human critical power oxygen uptake relationship at different pedalling frequencies. Exp Physiol 91, Beaver WL, Wasserman K & Whipp BJ (1973). On-line computer analysis and breath-by-breath display of exercise function tests. J Appl Physiol 34, Beaver WL, Wasserman K & Whipp BJ (1986). A new method for detecting anaerobic threshold by gas exchange. JAppl Physiol 60, Beelen A & Sargeant AJ (1991). Effect of fatigue on maximal power output at different contraction velocities in humans. J Appl Physiol 71, BenekeR&vonDuvillardSP(1996). Determination of maximal lactate steady state response in selected sports events. Med Sci Sports Exerc 28, Burnley M, Doust JH & Vanhatalo A (2006). A 3-min all-out test to determine peak oxygen uptake and the maximal steady state. Med Sci Sports Exerc 38, Carnevale TJ & Gaesser GA (1991). Effects of pedalling speed on the power-duration relationship for high-intensity exercise. Med Sci Sports Exerc 23, Davies CTM & Sandstrom ER (1989). Maximal mechanical power output and capacity of cyclists and young adults. Eur J Appl Physiol 58, Ferguson RA, Aagaard P, Ball D, Sargeant AJ & Bangsbo J (2000). Total power output generated during dynamic knee extensor exercise at different contraction frequencies. JAppl Physiol 89, Fukuba Y, Miura A, Endo M, Kan A, Yanagawa K & Whipp BJ (2003). The curvature constant parameter of the powerduration curve for varied-power exercise. Med Sci Sports Exerc 35, Gaesser GA & Poole DC (1996). The slow component of oxygen uptake kinetics in humans. ExercSportSciRev24, Hill DW (1993). The critical power concept. A review. Sports Med 16, Hill DW & Smith JC (1994). A method to ensure accuracy of estimates of anaerobic capacity derived using the critical power concept. J Sports Med Phys Fitness 34, Hill DW, Smith JC, Leuschel JL, Chasteen SD & Miller SA (1995). Effect of pedal cadence on parameters of the hyperbolic power-time relationship. IntJSportsMed16, Jones AM & Poole DC (2005). Introduction to oxygen uptake kinetics and historical development of the discipline. In Oxygen Uptake Kinetics in Sport, Exercise and Medicine,ed. Jones AM & Poole DC, pp Routledge, London. McCartney N, Heigenhauser GL & Jones NL (1983). Power output and fatigue of human muscle in maximal cycling exercise. J Appl Physiol 55, MacIntosh BR, Neptune RR & Horton JF (2000). Cadence, power, and muscle activation in cycle ergometry. Med Sci Sports Exerc 32, McNaughton L & Thomas D (1996). Effects of differing pedalling speeds on the power-duration relationship of high intensity cycle ergometry. Int J Sports Med 17, Monod H & Scherrer J (1965). The work capacity of a synergic muscular group. Ergonomics 8, Moritani T, Nagata A, devries HA & Muro M (1981). Critical power as a measure of physical work capacity and anaerobic threshold. Ergonomics 24, Morton RH & Billat LV (2004). The critical power model for intermittent exercise. Eur J Appl Physiol 91, Morton RH, Green S, Bishop D & Jenkins DG (1997). Ramp and constant power trials produce equivalent critical power estimates. Med Sci Sports Exerc 29, Poole DC, Ward SA, Gardner GW & Whipp BJ (1988). Metabolic and respiratory profile of the upper limit for prolonged exercise in man. Ergonomics 31, Pouilly J-P, Chatagnon M, Thomas V & Busso T (2005). Estimation of the parameters of the relationship between power and time to exhaustion from a single ramp test. Can J Appl Physiol 30, Sargeant AJ (1994). Human power output and muscle fatigue. IntJSportsMed15, Sargeant AJ, HoinvilleE&Young A (1981). Maximum leg force and power output during short-term dynamic exercise. J Appl Physiol 51, Smith JC & Hill DW (1993). Stability of parameter estimates derived from the power/time relationship. Can J Appl Physiol 18, Suzuki Y (1979). Mechanical efficiency of fast- and slow-twitch muscle fibers in man during cycling. J Appl Physiol 47, Vanhatalo A, Doust JH & Burnley M (2007). Determination of critical power using a 3-min all-out cycling test. Med Sci Sports Exerc 38, Whipp BJ & Mahler M (1980). Dynamics of pulmonary gas exchange during exercise. In Pulmonary Gas Exchange,ed. West JB, pp Academic Press, New York.