Theoretically, the critical power (CP) test provides 2 distinct parameters that reflect aerobic and anaerobic capabilities called CP and anaerobic work capacity (AWC), respectively (26,27). The CP is an estimate of the asymptote of the power output (P) vs. time-to-exhaustion relationship (Figure 1A) and represents the highest P that can be maintained for an extended period of time (33). The AWC is a measure of the total work that can be performed using only stored energy sources within the muscle including adenosine triphosphate, phosphocreatine, glycogen, and the oxygen bound to myoglobin (4,26,27). Both CP and AWC have a number of applications in laboratory and clinical settings. For example, it has been suggested that CP is the highest P associated with the maintenance of intramuscular homeostasis and demarcates the heavy from severe exercise intensity domains (3,13,20,31-33). In addition, CP and AWC have been used to prescribe and examine the effectiveness of exercise training programs (3,18,19,28), predict endurance exercise performance (12,15), examine the mechanisms of fatigue (3,16), assess the exercise capacity of patients with chronic obstructive pulmonary disease (COPD) (30), and determine the efficacy of nutritional supplements (22,38).
Moritani et al. (27) proposed a cycle ergometer analog of the original critical force and critical power (CPPT test) tests of Monod and Scherrer (26) for isometric, intermittent isometric, and dynamic muscle actions. The CPPT test for cycle ergometry relates the amount of work performed to exhaustion or work limit (W lim) and the time to exhaustion or time limit (T lim) for a series of work bouts at different power outputs (Figure 1B). The CP is the slope, and AWC is the y-intercept of the W lim vs. T lim relationship.
The practicality of the CPPT test is limited by the need for subjects to perform multiple (typically 3–5) exhaustive work bouts (11,27). Therefore, recent studies (6,10,35) have proposed a single, 3-minute, all-out cycle ergometer test (CP3min) for estimating CP and AWC. Originally, Burnley et al. (6) defined the end power (EP) as the average P over the last 30 seconds of the exhaustive 3-minute test and the work above end power (WEP) as the integral of the P vs. time relationship above the EP across the entire 3-minute test (Figure 2). Vanhatalo et al. (35) compared the EP and WEP with CP and AWC from the CPPT test. The results indicated that there were no significant differences for CP and WEP from the CP3min test (EP = 287 ± 55 W; WEP = 15.0 ± 4.7 kJ) vs. CP and AWC from the CPPT test (287 ± 56 W; AWC = 16.0 ± 3.8 kJ). Furthermore, EP and CP were correlated at r = 0.99, and WEP and AWC were correlated at r = 0.84 (35). Thus, the findings of Vanhatalo et al. (35) suggested that CP and AWC could be estimated from a single work bout using the CP3min test.
Although a single 3-minute, all-out work bout is less physically demanding than the multiple exhaustive work bouts used to estimate CP and AWC from the CPPT test, the CP3min test (6,35) also requires a maximal cycle ergometer test to assess O2peak and gas exchange threshold (GET). These parameters are then used to determine the P for the CP3min test to estimate CP and AWC (35-37). A 3-minute, all-out test that uses a P based on body weight would eliminate the need for the measurement of gas exchange parameters and a maximal incremental cycle ergometer test and, thus, provide a more practical way to estimate CP and AWC. Therefore, the purpose of this study was to develop a 3-minute, all-out test protocol using the Monark cycle ergometer for estimating CP and AWC with the resistance based on body weight. Based on previous studies (6,10,26,27,35-37), we tested the hypothesis that a 3-minute, all-out test on a Monark cycle ergometer, with the resistance set at 3.5 or 4.5% of the subject's body weight (CP3.5% and CP4.5% tests), would provide accurate estimates of CP and AWC when compared with those from the CPPT (27) and CP3min tests (6,35).
Experimental Approach to the Problem
The subjects visited the laboratory on 8 occasions, with 24–48 hours between visits. During the first visit, the subjects performed an incremental cycle ergometer test to exhaustion for the determination of O2peak and GET. During the next 4 visits, the subjects completed the CPPT test, which included 4 randomly ordered, constant P rides to exhaustion to determine CP and AWC (27). The next visit included the CP3min test to determine EP and work done above end power WEP (6). Theoretically, the EP and WEP correspond to CP and AWC, respectively (35). The final 2 visits were the CP3.5% and CP4.5% tests performed in random order to estimate CP and AWC. The resistances of 3.5 and 4.5% of the subject's body weight were chosen for the CP3.5% and CP4.5% tests based on pilot data collection from 2 subjects. The pilot data collection included 4 separate 3-minute all-out tests with resistance set at 3.5, 4.5, 5.0, and 6.0% of the subject's body weight. The results indicated that the estimates of CP and AWC were similar to the CPPT for the resistance of 3.5 and 4.5%. Critical power, however, was overestimated by 11–19%, and AWC was underestimated 20–30% for the 3-minute all-out tests with the resistances of 5.0 and 6.0%.
Six male and 6 female subjects (mean ± SD: age 23.2 ± 3.5 years, body mass 71.4 ± 12.1 kg, and height 175 ± 8 cm) volunteered for this study. The subjects were moderately trained (1), and none were competitive cyclists. According to the American College of Sports Medicine (1), moderate training includes aerobic activity performed for a minimum of 30 minutes 5 times a week. Specifically, the subject's physical activities included running (n = 11), cycling (n = 3) and recreational sports (n = 1). This study was approved by the University Institutional Review Board for Human Subjects, and all the subjects completed a health history questionnaire and signed a written informed consent document before testing.
Determination of O2peak and Gas Exchange Threshold
Each subject performed an incremental test to exhaustion on a calibrated Quinton (Corval 400) electronically braked cycle ergometer (Quinton Instruments Inc., Seattle, WA, USA) at a pedal cadence of 70 rev·min−1. The ergometer seat height was adjusted so that the subject's legs were near full extension at the bottom of the pedal revolution. Toe clips were used to maintain pedal contact throughout the test. All the subjects wore a nose clip and breathed through a 2-way valve (Hans Rudolph 2700 breathing valve, Kansas City, MO, USA). Expired gas samples were collected and analyzed using a calibrated TrueMax 2400 metabolic cart (Parvo Medics, Sandy, UT, USA). The gas analyzers were calibrated with room air and gases of known concentration before all testing sessions. The O2, CO2, and ventilatory parameters were expressed as 30-second averages. The subjects were fitted with a Polar Heart Watch system (Polar Electro Inc., Lake Success, NY, USA). The test began at 30 W, and the power output was increased by 30 W every 2 minutes until voluntary exhaustion or the subject's pedal rate decreased to <70 rev·min−1 for >10 seconds, despite strong verbal encouragement being given. The O2peak was defined as the highest O2 value in the last 30 seconds of the test that met 2 of the following 3 criteria (9): (a) 90% of age-predicted maximum heart rate; (b) respiratory exchange ratio >1.1; and (c) a plateau of oxygen uptake (<150 ml·min−1 in O2 over the last 30 seconds of the test).
The GET was determined using the V-slope method described by Beaver et al. (2). The GET was defined as the O2 value corresponding to the intersection of 2 linear regression lines derived separately from the data points below and above the breakpoint in the CO2 vs. O2 relationship.
Critical Power Test
Critical power and AWC were determined on the Calibrated Quinton Corval 400 (Quinton Instruments Inc.) electronically braked cycle ergometer, using the procedures of Moritani et al. (27) with the power outputs based on the recommendations of Vanhatalo et al. (35). The subjects rode to exhaustion at 4 separate power outputs equal to 70 and 80% Δ (i.e., GET + 70% Δ and 80% Δ, where Δ was the magnitude of the interval between GET and O2peak) and 100 and 105% O2peak (35). The subjects pedaled at 70 rev·min−1, and the test was terminated when the subject could no longer maintain 65 rev·min−1, despite strong verbal encouragement being given (14). The subjects were not aware of the power output or elapsed time during any of the rides. The CPPT test has a high test-retest correlation with intraclass correlation coefficient (ICC) values that range from 0.90 to 0.96 (11).
The 2-parameter, linear, work limit (W lim) vs. time limit (T lim) model (Figure 1B) was used to estimate CP and AWC from the 4 power outputs (27). The CP was defined as the slope (b) coefficient of the regression line (expressed in watts), whereas AWC was the y-intercept (a) of this relationship (expressed in joules). Theoretically, the CP is the asymptote of the hyperbolic P vs. T lim relationship (Figure 1A) (26,27).
Three-Minute All-Out Test
Critical power and AWC from the CP3min test were determined on the calibrated Quinton Corval 400 (Quinton Instruments Inc.) electronically braked cycle ergometer, using the procedures of Vanhatalo et al. (35). To be consistent with the terminology of Moritani et al. (27), the terms CP and AWC were used to represent the EP and WEP, respectively, as described by Vanhatalo et al. (35). Each subject completed a warm-up at 50 W for 5-minute followed by 5 minutes of rest. The test began with unloaded cycling at 90 rev·min−1 for 3 minutes followed by a 3 minute all-out effort. The subjects were instructed to increase the pedaling cadence to 110 rev·min−1 in the last 5 seconds of the unloaded phase and then maintain the cadence as high as possible throughout the CP3-min test. The resistance for the CP3min test was set using the linear mode of the Calibrated Quinton Corval 400 (Quinton Instruments Inc.) electronically braked cycle ergometer (linear factor = power/cadence2). The linear factor was calculated as the power output halfway between O2peak and GET (GET + 50% Δ) divided by a cadence of 70 rev·min−1 squared (6). Thus, the linear factor was equal to GET + 50% Δ/(70 rev·min−1)2. To prevent pacing and ensure an all-out effort, the subjects were not made aware of the elapsed time, and strong verbal encouragement was provided.
The estimates of CP and AWC from the CP3min test were determined from the P vs. time relationship (Figure 2). Critical power was the average P over the final 30 seconds of the test. The AWC was calculated as the integral of the P vs. time relationship above CP using custom LabVIEW software (version 8.5, National Instruments, Austin, TX, USA).
Monark 3-Minute All-Out Tests
A Monark cycle ergometer (model 818) was used for the CP3.5% and CP4.5% tests to estimate CP and AWC. The seat height was adjusted as previously described. The subjects completed a warm-up at 1 kg for 5 minutes. The test began when the subjects reached 110 rev·min−1, and the resistance was applied. The subjects pedaled with an all-out effort for 3 minutes. Resistances were randomized at 3.5% (CP3.5% test) and 4.5% (CP4.5% test) of body weight (0.035 or 0.045 × body weight in kilograms). These values (0.035 and 0.045) were selected based on pilot data, which indicated that these percentages of body weight could potentially be used to estimate CP and AWC. The subjects were not aware of the elapsed time or P. Strong verbal encouragement was provided. Pedal revolutions were recorded every 5 seconds using SMI software (Sports Medicine Industries, Inc., St. Cloud, MN, USA). The CP was the average P for the final 30 seconds of the test, and AWC was calculated as the integral of the P vs. time relationship above CP (Figure 2).
Mean differences between estimates of CP and AWC derived from the 4 methods (CPPT, CP3min, CP3.5%, and CP4.5%) were analyzed using separate 1-way repeated measures ANOVAs (p ≤ 0.05). Post hoc comparisons were conducted with paired t-tests and Bonferroni corrections (Table 1). The relationships among the 4 estimates of CP and AWC were described using Pearson product-moment correlations and separate zero order correlation matrices. The analyses were conducted using Statistical Package for the Social Sciences software (v.19.0. SPSS Inc., Chicago, IL, USA).
The mean (±SD) O2peak for the subjects in this study was 3.02 ± 0.73 L·min−1 (42.97 ± 7.42 ml·kg−1·min−1). In addition, the maximal power output from the incremental test to exhaustion was 225 ± 58 W and the GET was 2.16 ± 0.47 L·min−1 (30.73 ± 4.02 ml·kg−1·min−1). The GET occurred at 72 ± 6% of O2peak.
The r 2 values for the W lim vs. T lim relationships used for the CPPT test ranged from 0.98 to 0.99. The CP values for the CPPT test ranged from 103 to 256 W, and the AWC values ranged from 7,596 to 25,775 J (Table 1). There were no significant mean differences among CP values from the CPPT (178 ± 47 W), CP3.5% (173 ± 40 W), and CP4.5% (186 ± 44 W) tests. The mean CP from the CP3min test (193 ± 54 W), however, was significantly greater than those from the CPPT and CP3.5% (Table 1) tests. In addition, the CP values from the 4 tests were highly intercorrelated at r = 0.90–0.97.
There were no significant mean differences among AWC values for the CPPT (13,412 ± 6,247 J), CP3min (10,895 ± 2,923 J), and CP4.5% (9,842 ± 4,394 J) tests. The AWC values from the CPPT and CP3min tests, however, were significantly greater than that from the CP3.5% (8,357 ± 2,946 J) (Table 1) test. Furthermore, the AWC values from the 4 tests were highly intercorrelated at r = 0.76–0.91.
The mean (±SD) O2peak values for the male (42.52 ± 7.21 ml·kg−1·min−1) and female (43.42 ± 8.27 ml·kg−1·min−1) subjects in this study resulted in cardiorespiratory fitness classifications of “fair” and “excellent,” respectively (1). The mean GET for the total sample (n = 12), which was used to set the power output for the CP3min test, was 30.73 ± 4.02 ml·kg−1·min−1. These GET values (72 ± 6% of O2peak) were typical of those previously reported for untrained to moderately trained (54–75% O2peak) subjects (7,8,21,34).
The W lim vs. T lim relationships (Figure 1B) for the CPPT tests were highly linear at r 2 = 0.98–0.99. These results were consistent with previous findings (5,17,27,29) that have reported coefficients of determination of r 2 = 0.98–1.00 for the linearity of the W lim vs. T lim relationships. In addition, the range of CPPT values in this study (103–265 W) (Table 1) was similar to those of Moritani et al. (27) for untrained subjects (114–262 W), but less than those of more highly fit subjects (270–348 W) (17). The range of AWC values from the CPPT test in this study was 7,596–25,775 J (Table 1), which were similar to the values for untrained subjects (6,777–23,169 J) reported in a previous study (15). These AWC values, however, were somewhat lower than those reported (10,300–30,500 J) by Jenkins and Quigley (17) for trained cyclists.
In this study, the CP3min,, CP3.5%, and CP4.5% tests resulted in patterns of responses (Figures 2–4) for the power output vs. time relationships that were consistent with that of the 3 minute, all-out test of Burnley et al. (6) and Vanhatalo et al. (35). These patterns involved initial increases in power output during the first 5–10 seconds, followed by steep declines throughout the first 2 minutes of the tests. The final 1 minute of the tests resulted in gradual decreases in power outputs that plateaued over the final 30 seconds.
We hypothesized that there would be no significant differences among CP estimates from the CPPT, CP3min, CP3.5%, and CP4.5% tests. The results showed no mean differences among the CPPT (178 ± 47 W), CP3.5% (173 ± 40 W), and CP4.5% (186 ± 44 W) tests. However, the mean CP value from the CP3min test (193 ± 54 W) was significantly (p = 0.02) greater than the CPPT and CP3.5% tests but not significantly different from the CP4.5% test (Table 1). These findings differed from those of Vanhatalo et al. (35) who reported no significant difference between the CP3min (287 ± 55 W) and the CPPT (287 ± 56 W) tests at a pedaling cadence of 80–90 rev·min−1 for highly trained cyclists and runners. At a cadence of 100 rev·min−1, however, Vanhatalo et al. (36) reported a lower CP value from the CP3min test (244 ± 41 W) than at 80–90 rev·min−1 (254 ± 40 W). It is possible, therefore, that the lower cadence used in this study (70 rev·min−1) contributed to the difference between the results of this study and those of Vanhatalo (35). We selected a pedaling cadence of 70 rev·min−1 because (a) previous studies (23-25) have reported that untrained subjects typically select a preferred cadence of 60–80 rev·min−1 and (b) Burnley et al. (6) set the resistance on the electronically braked cycle ergometer using the same cadence as the incremental test to exhaustion. Future studies should examine the effect of pedaling cadence on differences between estimates of CP from the CPPT and CP3min tests in trained and untrained subjects.
The results of this study indicated that there were no significant mean differences for estimates of CP and AWC from the CPPT, CP3min, and CP4.5% tests (Table 1). Furthermore, the CP values from these 3 tests were highly intercorrelated at r = 0.90–0.97. In addition, the AWC values were moderately to highly intercorrelated r = 0.76–0.91. Thus, the current findings indicated that CP and AWC could be estimated from a 3-minute, all-out test on a Monark cycle ergometer with the resistance set at 4.5% of the subject's body weight (CP4.5%). A salient feature of the CP4.5% test is that it requires only the measurement of the subject's body weight and a single work bout on a Monark cycle ergmometer. The original CP test requires a minimum of 2, but usually ≥3, rides to exhaustion on a cycle ergometer to estimate CP and AWC (14,27). In addition, the method (CP3min) proposed by Burnley et al. (6) requires the measurement and analysis of expired gas samples during an incremental test to exhaustion on an electronically braked cycle ergometer for the determination of GET, before the 3-minute, all-out test. Therefore, the CP4.5% test provides a more practical and easily administered method for determining CP and AWC than either the original procedure (CPPT) of Moritani et al. (27) or the single work bout alternative (CP3min) of Burnley et al. (6).
The mean CP and AWC values estimated from the CP3.5% test were significantly less than those of the CP3min test (Table 1). Specifically, the CP3.5% test underestimated CP and AWC by 10–23%, respectively, compared with the CP3min test. In addition, the CP3.5% test underestimated the AWC by 38% compared with the CPPT test. Even though there were no significant mean differences between the CP and AWC values from the CP3.5% and CP4.5% tests, the CP4.5% test is recommended because of its similarities to the results of the CPPT and CP3min tests. Thus, the current findings indicated that using a resistance of 4.5% of body weight provided more accurate estimates of CP and AWC than using a resistance of 3.5% of body weight when compared with the original CP test of Moritani et al. (27) and the single work bout, 3-minute, all-out CP test of Burnley et al. (6).
In summary, the results of this study indicated that CP and AWC could be estimated from a single, 3-minute, all-out, test on a Monark cycle ergomter with the resistance set at 4.5% of the subject's body weight. In this study, it was found that (a) unlike Vanhatalo et al. (35), there was a significant mean difference between estimates of CP from the CPPT and CP3min tests, possibly because of the lower pedaling cadence selected in this study and (b) CP and AWC could be accurately estimated from the CP4.5% test but not the CP3.5% test. Thus, the advantages of the CP4.5% test over the CPPT and CP3min tests are (a) the CP4.5% tests requires only 1 work bout compared with multiple, exhaustive work bouts for the original CP test (CPPT) of Moritani et al. (27); (b) the CP4.5% test uses a resistance set according to the body weight of the subject as opposed to the need to collect and analyze gas exchange variables during an incremental test to exhaustion for the determination of GET to set the resistance for the CP3min test of Burnley et al. (6); and (c) the CP4.5% test involves a single, 3-minute, all-out, work bout on a Monark cycle ergometer, whereas the CP3min test requires an electronically braked cycle ergometer. Therefore, the CP45% test is recommended as a new practical and accurate method for estimating CP and AWC.
The CP test provides parameters that reflect both aerobic and anaerobic metabolism that can be used to demarcate the heavy from severe exercise intensity domains, assess fitness, prescribe training intensities, and predict exercise performance. A salient feature of the CP4.5% test proposed in this study is that it requires only the measurement of the subject's body weight and a single work bout on a Monark cycle ergmometer. The original CP test (CPPT) requires a minimum of 2, but usually ≥3, rides to exhaustion on a cycle ergometer to estimate CP and AWC (14,27). In addition, the method (CP3min) proposed by Burnley et al. (6) requires the measurement and analysis of expired gas samples during an incremental test to exhaustion on an electronically braked cycle ergometer, before the 3-minute, all-out test. Therefore, the CP4.5% test provides a more practical and easily administered method for determining CP and AWC than either the original procedure (CPPT) of Moritani et al. (37) or the single work bout alternative (CP3min) of Burnley et al. (6).
There were no sources of external funding for this work. The results of this study do not constitute an endorsement by the authors or the National Strength and Conditioning Association.
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Keywords:© 2012 National Strength and Conditioning Association
Monark cycle ergometer; fatigue thresholds; 3-minute all-out test; body weight base