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???? GAZZ MED ITAL - ARCH SCI MED 2011;170:1-2
Received on January 14, 2011. Accepted for publication on October 28, 2011. Corresponding author: J. Coquart, Faculty of Sports Sciences and Health Sciences, 9 rue de l’Université, 59790 Ronchin, France. E-mail:
[email protected]
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1Germon and Gauthier Hospital Clinical Research Unity, Béthune, France 2Univ Lille Nord de France, F-59000 Lille, France 3UDSL, EA3608, F-59790, Ronchin, France 4School of Sport and Health Sciences University of Exeter, Exeter, UK 5Department of Pneumology Germon and Gauthier Hospital, Béthune, France
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oaches frequently evaluate their athletes in order to estimate their maximal physical capacity (e.g., maximal oxygen uptake: ∙ ∙ V O2 max). The assessment of V O2 max facilitates the prescription of optimal exercise intensities (e.g., work rates equivalent to ∙ 90% V O2 max), the evaluation of the effects ∙ of the training program on V O2 max 1 and reevaluations of exercise intensity thresholds such as critical power or lactate thresholds. However, the direct assessment of ∙ V O2 max requires maximal effort, and such exhaustive tests may not always be well accepted by athletes, as they may be apprehensive about the possible impairment of performance in subsequent days due to the high level of physical effort required by the tests.2 Consequently, a number of studies have explored and confirmed the utility of various submaximal exercise tests and pro∙ tocols to provide estimates of V O2 max. Effort perception, defined as the intensity of subjective effort, stress, discomfort and fatigue felt during physical activity, is very
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Aim. The purpose of this study was to test the validity and the accuracy of estimating maximal oxygen uptake (VO2max) from ratings of perceived exertion (RPE), during submaximal tests in competitive cyclists. Methods. Twelve competitive cyclists performed a graded exercise test (GXT) and a test with randomised workloads (TRW) on a cycle ergometer. Oxygen uptake (VO2) and RPE were measured at 150, 200, 250 and 300 Watts (W) during both tests, and actual VO2max was also determined at the end of the GXT. Individual linear regressions between VO2 and RPE were extrapolated to RPE 19 in order to estimate VO2max from each test. Actual and estimated VO2max from GXT and TRW were not significantly different (65.0±6.9, 68.3±8.8 and 73.1±12.0 ml.kg-1. min-1, respectively; P>0.05). Results. The estimated VO2max were significantly correlated to actual VO2max whatever the test (P≤0.05; r≥0.57). The bias and the 95% limits of agreement analysis represented -3.3±14.5 and -8.1±17.7 ml.kg-1.min-1 for GXT and TRW, respectively. Conclusion. The results suggested that only RPE elicited during a sub-maximal GXT may be used to estimate VO2max in competitive cyclists. Key words: Exercise test - Sports - Oxygen consumption.
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Estimation of maximal oxygen uptake from ratings of perceived exertion elicited during sub-maximal tests in competitive cyclists
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ESTIMATION OF MAXIMAL OXYGEN UPTAKE IN COMPETITIVE CYCLISTS
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Materials and methods
Participants
Twelve male competitive cyclists at a regional level (age: 22.3±4.1 y, body mass: 69.7±7.2 kg, height: 178±7 cm, body fat: 12.3±2.0%) volunteered to take part in this study. All participants were experienced (8.5±3.9 yr) in cycling. None of the participants reported respiratory or cardiac disease, or were known to be suffering from any chronic disease. None of the participants were taking medications and all were non-smokers. Prior to the first test, all participants provided written informed consent concerning the investigation purposes and procedures. Moreover, this study was approved by the local Ethics Committee for participants’ protection in clinical research and the technical committee for clinical hospital research.
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piratory and muscular work than the TRW for similar perceptually-based values. The TRW consists of performing 4 pedalling periods in a randomised order. In this protocol, the cyclists are unaware of the order of workloads and they are forced to focus very strongly on the internal signals to give perceptually-based values which correspond faithfully to their sensations of effort.8 This being the case, it may be suggested that the ∙ relationship between RPE and V O2 would ∙ enable V O2 max to be predicted with more accuracy during TRW rather than GXT. To our knowledge, no study has tested this hypothesis. Consequently, the purpose of the current study was to test the validity and the accu∙ racy of predicting V O2 max from RPE, during sub-maximal tests on a cycle ergometer, in competitive cyclists.
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useful measure which can be applied in many sporting applications.3 The most frequently used tool for measurement of effort perception is the Ratings of Perceived Exertion scale (RPE).4 This scale was constructed by Gunnar Borg 5 from the basic assumption that physiological strain grows linearly with exercise intensity, and that effort perception follows the same linear increase.6 Several studies confirm this assumption as numerous physiological variables increasing with exercise intensity were found to be significantly correlated to RPE.7, 8 Among these physiological variables, it is widely recog∙ nized that oxygen uptake (V O2 ) is one of the main mediators of RPE.3 A number of studies have therefore extrapolated the line of best fit through the linear regression of ∙ sub-maximal RPE and V O2 to RPE 19 or 20, ∙ in order to predict V O2 max.9-15 Eston et al.9 were the first researchers to use a perceptu∙ ally regulated protocol to predict V O2 max with acceptable accuracy, in physically active men. From their study, it was concluded ∙ that the RPE scale allows the V O2 max to be estimated with acceptable accuracy from an exercise test in which the participant was required to exercise at five self-regulated RPE levels 9, 11, 13, 15, 17 prescribed in an incremental fashion (i.e., a perceptually regulated graded exercise test). Subsequent studies have confirmed this observation in obese women,15 healthy and sedentary participants,11-12, 14 participants of low 12, 16 or high fitness,11 physically active participants,10, 12 physically active women who were members of various sports clubs,13 during a graded exercise test (GXT) on a cycle ergometer,12, 15, 16 during incremental, perceptually-regulated graded exercise test on a cycle ergometer 12, 14 and randomized perceptually-regulated exercise tests17 or even a running multistage fitness test.13 However, to our knowledge, no study has analyzed the validity of predicting ∙ V O2 max from sub-maximal RPE in competitive athletes. Recently, Coquart et al.8 proposed the use of perceptually-based values in trained cyclists during a test with randomized workloads (TRW) rather than a GXT because the GXT generated higher cardiores-
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Materials The height, body mass and skinfold thickness of each participant were measured with a wall stadiometer (model 220, Seca®, Hamburg, Germany), a calibrated
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ESTIMATION OF MAXIMAL OXYGEN UPTAKE IN COMPETITIVE CYCLISTS
The tests were preceded by a 3-min rest period (sitting on the cycle ergometer) followed by 8-min warm-up period at 100W, then a 5-min passive recovery period. Graded
exercise test
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Before the first test, the anthropometric data (height, body mass, percentage of body fat) were measured. Percentage of body fat was estimated from skinfold thickness measured at 4 sites (biceps, triceps, subcapular and suprailiac) in accordance with the method of Durnin and Womersley18. All participants performed GXT and TRW, in counterbalanced order and on different days. Moreover, the tests were performed on the same cycle ergometer.
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with randomised workloads
The TRW consisted of alternating 4-min pedalling periods with 8-min passive recovery periods. After each recovery period, the workload was progressively increased for 1 min until the desired power output was reached. During the pedalling periods, the workloads were 150, 200, 250 and 300W, in a randomised order. A maximal power of 300W was chosen so that all participants fully completed the tests. To avoid the possibility of a participant knowing the actual power output the computer screen was hidden from the participant’s view at all times.
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Test
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During GXT, the initial power output was set at 150W for 4 min then increased by 50W every 4 min, until 300W. After this stage, an increment of 25W was administered every 2 min. The participants were instructed to develop the highest possible level of power. Exhaustion was verified by following crite∙ ria: 1) a plateau phenomenon in V O2 ; 2) respiratory exchange ratio value ≥ 1.1; 3) peak heart rate±10 bpm of the predicted maximal heart rate (220 - age); 4) blood lactate concentration after test cessation >10 mmol.L-1; and 5) RPE ≥ 18 at test cessation. At least three of the five criteria were met or the test was repeated.
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scale (TBF 543, Tanita®, Tokyo, Japan) and a skinfold calliper (HSK-B1, Body Care®, Warwickshire, United Kingdom), respectively. Respiratory gas analysis was carried out via a breath-by-breath system with an opencircuit metabolic card (Ergocard, Medisoft®, Sorinnes, Belgium). This respiratory gas analysis system was calibrated in accordance with the manufacturer’s guidelines using a 3-liter syringe (Calibration pump, Medisoft®, Sorinnes, Belgium) for volume calibration, and ambient air and a gas of known oxygen and carbon dioxide concentrations (16% and 4%, respectively) for gas calibration. The software used was Exp’air (Medisoft®, Sorinnes, Belgium). Effort perception was expressed using the RPE scale of Borg5. This scale comprises fifteen numerical ratings (between 6 and 20) associated with verbal cues, from “7 = very very light” to “19 = very very hard”. The participant was asked, “How hard do you feel this exercise is?” Maximal heart rate was recorded with a 12-lead electrocardiogram (Medcard, Medisoft®, Sorinnes, Belgium) linked with the respiratory gas analysis system. The lactate concentration at exhaustion was determined by the ABL800Flex (Radiometer Medical®, Copenhague, Danemark). The tests were conducted on an electromagnetically braked cycle ergometer (Ergometrics 800, Ergoline®, Blitz, Germany) which maintained the set power output by adjusting the resistance with variations in pedal rate.
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Perceptual
anchoring
In a preliminary session, the participants were familiarized with the RPE scale using the exercise anchoring procedure and a copy of the scale was provided for each participant to use during training sessions. Moreover, the instructions on the scales were read to the participants before each test, to help them to link their full exercise stimulus range with their full ratings of perceived exertion response range. Further-
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ESTIMATION OF MAXIMAL OXYGEN UPTAKE IN COMPETITIVE CYCLISTS
Statistical analysis
standardization
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Before the first test, the seat and handlebar heights were set by each participant and kept constant for the second test. The participants were not verbally encouraged before they had entirely completed the four first stages of GXT. The temperature of the air-conditioned room was always maintained between 20 and 24°C. The tests were conducted at the same time of day with a period of 7 to 14 days between both. All tests were carried out under medical supervision. The last meal was standardised and consumed 2 hours prior to beginning the exercise session. This meal comprised approximately 3027 kJ (74.4% carbohydrate, 22.6% protein, 3.0% fat), and it was consumed between 11.30 a.m. and 12.30 p.m. within the laboratory, and only water was drunk. The participants were instructed to main4
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Tests
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Data are expressed as means±standard deviations (SD). To investigate whether sub-maximal RPE could be used to pre∙ dict V O2 max, the individual linear regres∙ sion between RPE and V O2 at 150, 200, 250 and 300W was extrapolated to the theoreti∙ cal V O2 max at RPE 19 (for each test). The ∙ equation used was: V O2 max = a + b (RPE 19). The RPE 19 rather than RPE 20 was used in this study as previous research has shown that RPE 19 is the maximal RPE that an individual will generally tolerate during exhaustive bouts of exercise.11, 12 Normal Gaussian distributions of the data ∙ (actual and predicted V O2 max) were verified by the Shapiro-Wilks test, and homogeneity of variance by the Levene test. Oneway analysis of variance (ANOVA) was used ∙ to compare actual and predicted V O2 max. If significant differences were obtained, a Bonferroni post-hoc test was conducted. The Pearson product moment correlation and Bland-Altman plots 19 were used to evaluate the association and the level of agreement ∙ between actual and predicted V O2 max. The Bland-Altman plot 19 requires the calculation of the mean difference (bias) between actual ∙ and predicted V O2 max, as well as±1.96 SD of these differences (95% limits of agreement, LoA). Before the Bland-Altman plot, the normality of the distribution of the differences ∙ between actual and predicted V O2 max was attested with the Shapiro-Wilk test and homoscedasticity with a Levene test. Moreover, we tested the null hypothesis that the bias was not different from zero with one-way ANOVA. Finally, the lack of significant relationship between the bias and the difference ∙ between actual and predicted V O2 max was tested using a Bravais-Pearson test.
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Recent research on a cycle ergometer has demonstrated more reliable perceptions of exertion from the overall rather than the peripheral sensation (i.e., from muscular sensations).11 As such, the overall sensation of exertion was requested throughout each exercise test. The RPE were collected during the last 30s of the first 4 stages (i.e., at 150, 200, 250, 300W). The oxygen uptake was recorded breathby-breath then averaged during the last 30s of the 4 first stages both tests and at the end of GXT. Respiratory exchange ratio to exhaustion was determined during GXT and maximal heart rate was recorded in order to check the exhaustion during GXT. Venous blood samples were drawn from a superficial forearm vein at the end of GXT. The blood lactate concentration was measured immediately after sampling.
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Measurements
tain their normal diet during the last few days preceding the tests, to refrain from alcohol consumption 24 h before each test, and caffeine on the tests day. Similarly, the participants were asked to avoid strenuous physical activity during the two days prior to the tests and not to exercise on the day of a test.
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more, at the end of the warm-up period, RPE was measured so that the participants could refer to them and thus avoid a lack of perceptual references during the first workload of tests.
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Table I.—Maximal physiological (oxygen uptake, heart rate, respiratory exchange ratio, blood lactate concentration) and perceptual (rating of perceived exertion) responses elicited at termination of the graded exercise test (maximal work rate). Maximal oxygen uptake (ml.kg-1.min-1)
Maximal heart rate (bpm)
Maximal respiratory exchange ratio
Maximal blood lactate concentration (mmol.L-1)
Terminal Rating of Perceived Exertion
Maximal work rate (W)
65.0 ± 6.9
190 ± 7
1.10 ± 0.04
11.9 ± 2.9
19.3 ± 1.1
341 ± 23
Workloads (W) 300
47.9 ± 5.4 50.7 ± 7.4
63.8 ± 6.9 66.6 ± 10.7
75.0 ± 6.5 76.1 ± 6.6
87.0 ± 8.1 86.9 ± 10.3
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55 60 65 70 75 80 85 90 Estimated maximal oxygen uptake (ml · kg-1 · min-1)
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Table II.—Percentage of maximal oxygen uptake at workloads 150, 200, 250 and 300W during the graded exercise test and the test with randomized workloads.
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50 55 60 65 70 75 80 85 90 95 Mean maximal oxygen uptake (ml · kg-1 · min-1)
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Figure 1.—A) Association between actual and predicted maximal oxygen uptake from graded exercise test. The dashed line is the line of identity which corresponds to a perfect estimation of maximal oxygen uptake. B) BlandAltman plots for the comparison between actual and predicted maximal oxygen uptake from graded exercise test. The dashed line is the bias (bias = -3.3 ml.kg-1.min-1). The thick lines are the 95% limits of agreement (LoA = 14.5 ml.kg-1. min-1). LoA correspond to±1.96 Standard Deviation (SD).
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Statistical significance was set at P0.05), these values were significantly different from 0 for the TRW (P=0.02). Moreover, the bias for TRW were significantly correlated with the differences between actual ∙ and predicted V O2 max (P=0.04; r=-0.61).
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Figure 2.—A) Association between actual and predicted maximal oxygen uptake from test with randomized workloads. The dashed line is the line of identity which corresponds to a perfect estimation of maximal oxygen uptake. B) Bland-Altman plots for the comparison between actual and predicted maximal oxygen uptake from test with randomized workloads. The dashed line is the bias (bias = -8.1 ml.kg-1.min-1). The thick lines are the 95% limits of agreement (LoA = 17.7 ml.kg-1.min-1). LoA correspond to±1.96 Standard Deviation (SD).
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The RPE is therefore considered to be an indicator of the maximal exercise duration that the athlete can perform at current exercise intensity. As the current study shows ∙ that the RPE is valid for predicting V O2 max (which is associated with the exercise endpoint during GXT), this study provides further confirmatory evidence of the teleoanticipation concept already observed in several studies.20, 22, 23
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The current study revealed that the RPE elicited during a sub-maximal GXT pro∙ vided a valid prediction of V O2 max in competitive male cyclists. Consequently, it is not necessary to perform the test to voluntary exhaustion in order to determine ∙ V O2 max. However, the accuracy of estimat∙ ed V O2 max may be sometimes insufficient for competitive cyclists. Riassunto
Stima del massimo apporto di ossigeno dalla valutazione dello sforzo percepito dedotto durante test submassimale nei ciclisti professionisti. Obiettivo. L’obbiettivo del presente studio è stato testare la validità e l’accuratezza della stima dell’apporto massimo di ossigeno (VO2max) dalla valutazione dello sforzo percepito (ratings of perceived exertion, RPE), durante test submassimale nei ciclisti professionisti. Metodi. Dodici ciclisti professionisti hanno eseguito un test di esercizio graduato (graded exercise test, GXT) ed un test con carico di lavoro randomizzato (randomised workloads, TRW) su una bicicletta-ergometro. L’apporto di ossigeno (VO2) e la RPE sono stati misurati a 150, 200, 250 e 300 Watts (W) durante entrambi i test, mentre la VO2max effettiva è stata determinata alla fine della GXT. La regressione lineare individuale tra la VO2 e la RPE sono state estrapolate dalla RPE 19 allo scopo di valutare la VO2max di ogni test. La VO2max effettiva e stimata dalla GXT e dalla TRW non erano significativamente differenti (65,0±6,9, 68,3±8,8 e 73,1±12,0 ml.kg-1.min-1, rispettivamente; P>0,05). Risultati. La VO2max stimata è risultata significativamente correlata alla VO2max effettiva in tutti i test (P≤0,05; r≥0,57). Il bias e i limiti al 95% dell’analisi della concordanza sono stati -3,3±14,5 and -8,1±17,7 ml.kg-1.min-1 rispettivamente per GXT e TRW.
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tive cyclists in the current study, the identified LoA mean that (in worst case scenario) ∙ a predicted V O2 max during a GXT might be 11.2 ml.kg-1.min-1 above or 17.8 ml.kg-1. ∙ min-1 below the actual V O2 max when ex∙ trapolating sub-maximal V O2 up to and including sub-maximal RPE to an RPE 19. This equates to a±21.8% margin of error ∙ between actual and predicted V O2 max. Although this margin of error was similar to some recent experimentations that ∙ used RPE≤15 to predict V O2 max in noncompetitive participants during GXT (approximately±18, 27 and 29% for Lambrick et al.,16 Coquart et al.15 and Faulkner and Eston,11 respectively); the predictive accuracy of this procedure may be considered to be low in competitive cyclists who want ∙ to know accurately V O2 max. Moreover, as 9, 10 some studies have reported lower 95% LoA when it used a perceptually-regulated GXT, this type of exercise test may be recommended rather than traditional GXT (or TRW) to improve the predictions accu∙ racy of V O2 max. Indeed, traditional GXT involves a process of passively estimating efforts from intensities (i.e., the participant undergoes the exercise intensity and provides RPE), while perceptually regulated GXT requires actively producing intensities from effort perceptions (i.e., the participant regulates the exercise intensity from RPE).9, 14 Consequently, perceptually-regulated GXT obliges the participants to focus on the exertion sensations, and probably to estimate RPE more accurately from internal signals.15 It has recently been suggested that at the onset of physical exercise, a central programmer estimates the time to volitional exhaustion that can safely be reached without causing absolute whole body energy depletion.20 In this concept, defined as “teleoanticipation” by Ulmer,21 the subjective prediction of the time limit is then associated to the higher RPE value that can be tolerated (i.e., RPE 19 or 20).20 Thus, during exercise, the RPE increases progressively until the attainment of RPE 19 (or 20), in proportion to the percentage of time remaining to complete the physical exercise.
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1. Garcin M, Coquart JBJ, Robin S, Matran R. Prediction of time to exhaustion in competitive cyclists from a perceptually-based scale. J Strength Cond Research. In press. 2. Sassi A, Marcora SM, Rampinini E, Mognoni P, Impellizzeri FM. Prediction of time to exhaustion from blood lactate response during submaximal exercise in competitive cyclists. Eur J Appl Physiol 2006;97:174-80. 3. Noble BJ, Robertson RJ. Perceived exertion. Champaign, IL: Human Kinetics; 1996. 4. Robertson RJ. Development of the perceived exertion knowledge base: an interdisciplinary process. Int J Sport Psychol 2001;32:189-96. 5. Borg G. Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med 1970;2:92-8. 6. Borg G. Borg’s Perceived exertion and pain scales. Champaign, IL: Human Kinetics; 1998 7. Chen MJ, Fan X, Moe ST. Criterion-related validity of the Borg ratings of perceived exertion scale in healthy individuals: a meta-analysis. J Sports Sci 2002;20:873-99. 8. Coquart JBJ, Legrand R, Robin S, Duhamel A, Matran R, Garcin M. Influence of successive bouts of fatiguing exercise on perceptual and physiological markers during an incremental exercise test. Psychophysiol�������������� ogy 2009;46:209-16. 9. Eston RG, Lamb KL, Parfitt CG, King N. The validity of predicting maximal oxygen uptake from a perceptually regulated graded exercise test. Eur J Appl Physiol 2005;94:221-7. 10. Eston RG, Faulkner JA, Mason EA, Parfitt G. The validity of predicting maximal oxygen uptake from perceptually regulated graded exercise tests of different durations. Eur J Appl Physiol 2006;97:535-41. 11. Faulkner JA, Eston RG. Overall and peripheral ratings of perceived exertion during a graded exercise test to volitional exhaustion in individuals of high and low fitness. Eur J Appl Physiol 2007;101:613-20.
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References
12. Faulkner JA, Parfitt G, Eston RG. Prediction ������������������� of maximal oxygen uptake from the ratings of perceived exertion and heart rate during a perceptually-regulated sub-maximal exercise test in active and sedentary participants. Eur J Appl Physiol 2007;101:397407. 13. Davies RC, Rowlands AV, Eston RG. The prediction of maximal oxygen uptake from sub-maximal ratings of perceived exertion elicited during the multistage fitness test. Br J Sports Med 2008;42:1006-10. 14. Eston RG, Lambrick D, Sheppard K, Parfitt G. Prediction of maximal oxygen uptake in sedentary males from a perceptually regulated, sub-maximal graded exercise test. J Sports Sci 2008;26:131-9. 15. Coquart JBJ, Lemaire C, Dubart A-E, Douillard C, Luttenbacher D-P, Wibaux F et al. Prediction of peak oxygen uptake from sub-maximal ratings of perceived exertion elicited during a graded exercise test in obese women. Psychophysiology 2009;46:1150-3. 16. Lambrick D, Faulkner JA, Rowlands A, Eston R. Prediction of maximal oxygen uptake from submaximal ratings of perceived exertion and heart rate during a continuous exercise test: the efficacy of RPE 13. Eur J Appl Physiol 2009;107:1-9. 17. Morris M, Lamb K, Cotterrell D, Buckley J. Predicting maximal oxygen uptake via a perceptually regulated exercise test (PRET). J Exerc Sci Fitness. In press. 18. Durnin JV, Womersley J. Body fat assessed from total body density and its estimation from skinfold thickness: Measurements on 481 men and women aged from 16 to 72 years. Br J Nut 1974;32:77-97. 19. Bland JM, Altman DG. Statistical methods for assessing agreement between twomethods of clinical measurement. The Lancet 1986;8:307-10. 20. Noakes TD, Snow RJ, Febbraio MA. Linear relationship between the perception of effort and the duration of constant load exercise that remains. J Appl Physiol 2004;96:1571-3. 21. Ulmer HV. Concept of an extracellular regulation of muscular metabolic rate during heavy exercise in humans by psychophysiological feedback. Experientia 1996;52:416-20. 22. Crewe H, Tucker R, Noakes TD. The rate of increase in rating of perceived exertion predicts the duration of exercise to fatigue at a fixed power output in different environmental conditions. Eur J Appl Physiol 2008;103:569-77. 23. Faulkner JA, Parfitt G, Eston RG. The ������������������ rating of perceived exertion during competitive running scales with time. Psychophysiology 2008;45:977-85.
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Conclusioni. I risultati suggeriscono che solo la RPE dedotta durante la GXT sub massimale può essere usata per stimare la VO2max nei ciclisti professionisti. Parole chiave: Esercizio fisico - Sport - Ossigeno, consumo.
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