1 3

Eur J Appl PhysiolDOI 10.1007/s00421-014-2891-0

OrIgInAl ArtIclE

Ramp‑incremented and RPE‑clamped test protocols elicit similar VO2max values in trained cyclists

Allison M. Straub · Adrian W. Midgley · Gerald S. Zavorsky · Angela R. Hillman

received: 23 October 2013 / Accepted: 7 April 2014 © Springer-Verlag Berlin Heidelberg 2014

protocol (mean difference = 0.002 l min−1; p = 0.97). Furthermore, no significant differences were observed for peak power output (p = 0.21), maximal minute ven-tilation (p = 0.97), maximal respiratory exchange ratio (p = 0.09), maximal heart rate (p = 0.51), and post-test blood lactate concentration (p = 0.58). the VO2max attained in the preferred protocol was significantly higher than the non-preferred protocol (mean difference = 0.14 l min−1; p = 0.03).Conclusion the rPE-clamped test protocol was as effec-tive as the ramp-incremented protocol for eliciting VO2max and could be considered as a valid alternative protocol, par-ticularly where a fixed test duration is desirable.

Keywords Aerobic capacity · cycle ergometry · Perceptually regulated exercise test · ratings of perceived exertion

Abbreviations[Bla] Blood lactate concentrationBMI Body mass indexHrmax Maximal heart ratePOpeak Peak power outputrErmax Maximal respiratory exchange ratiorPE ratings of perceived exertionrPM revolutions per minuteVEmax Maximal minute ventilationVO2max Maximal oxygen uptakeW Watt

Introduction

the measurement of cardiorespiratory fitness is important in both exercise science and clinical settings. common

Abstract Purpose the present study compared the efficacy of ramp incremented and ratings of perceived exertion (rPE)-clamped test protocols for eliciting maximal oxygen uptake (VO2max).Methods Sixteen trained cyclists (age 34 ± 7 years) per-formed a ramp-incremented protocol and an rPE-clamped protocol 1 week apart in a randomized, counterbalanced order. the rPE-clamped protocol consisted of five, 2-min stages where subjects self-selected work rate and pedal cadence to maintain the prescribed rPE. After complet-ing both test protocols subjects were asked which they preferred.Results the mean ± SD test time of 568 ± 72 s in the ramp protocol was not significantly different to the 600 ± 0 s in the rPE-clamped protocol (mean dif-ference = 32 s; p = 0.09), or was the VO2max of 3.86 ± 0.73 l min−1 in the ramp protocol significantly different to the 3.87 ± 0.72 l min−1 in the rPE-clamped

communicated by Peter Krustrup.

A. M. Straub · A. r. Hillman (*) Human Physiology laboratory, Marywood University, 2300 Adams Avenue, Scranton, PA 18509, USAe-mail: hillman@marywood.edu

A. W. Midgley Department of Sport and Physical Activity, Edge Hill University, Ormskirk, UK

g. S. Zavorsky Department of Health and Sport Sciences, University of louisville, louisville, KY, USA

g. S. Zavorsky Department of Physiology and Biophysics, University of louisville, louisville, KY, USA

Eur J Appl Physiol

1 3

applications include the evaluation of interventions such as physical training programs (Bhambhani and Singh 1985), exercise prescription (Midgley et al. 2006), diagnosis of chronic disease conditions (Arena and Sietsema 2011), and assessment of fitness for surgery (Struthers et al. 2008). consequently, accurate, reliable, and practically conveni-ent assessment of cardiorespiratory fitness has widespread interest. the maximal oxygen uptake (VO2max) is invari-ably accepted as the criterion measure of cardiorespiratory fitness and has been a primary focus of exercise-related research since its conception in the early 1920s (Hill and lupton 1923). Since its conception, technological innova-tions, mainly the introduction of automated metabolic gas analysis systems, have advanced the methodological aspects of VO2max determination (Macfarlane 2001). Despite these technological innovations, exercise physiologists are still debating basic methodological aspects of VO2max determina-tion, such as the characteristics of the VO2max test protocol.

noakes (2008) suggested that current ramp-incremented and step-incremented VO2max test protocols fail to elicit a true maximal effort because the body fatigues prematurely during such tests. By inference, this situation would likely result in individuals not attaining their true VO2max if the VO2 is still increasing at test termination, which is common during VO2max testing (Day et al. 2003; lucia et al. 2006). noakes (2008) argues that existing incremental exercise test protocols fail to utilize the brain in a similar manner to exercise training and competition and that, during a stand-ard VO2max test, the brain only has to decide when to stop exercising. the main issue is that, unlike natural training or competitive settings, during a VO2max test, subjects are unaware of the test endpoint and have no control over the work rate. Although, it is clear that subjects always have conscious control over the investment of effort and task disengagement (Al-rahamneh and Eston 2011), noakes suggests that a potential solution would be the use of self-paced protocols that would represent a more natural approach to maximal exercise testing and one that allows the body to relinquish homeostatic control and pacing strat-egy back to the brain.

the concept of the self-paced, or perceptually regu-lated, exercise protocol was conceived and first utilized in the late 1990s on cardiac patients medicated with beta-blockers (Eston and thompson 1997). Since that study, most notably in the last decade, a number of studies (Al-rahamneh and Eston 2011; Eston et al. 2005, 2006, 2008, 2012; Evans et al. 2013b; Faulkner et al. 2007; Morris et al. 2009, 2010) have adopted this concept for the prediction of VO2max from a submaximal perceptually regulated testing protocol, where each exercise test stage is associated with (clamped to) a specific number on Borg’s 6–20 ratings of Perceived Exertion (rPE) Scale (Borg 1990). A thorough, comprehensive review of such studies has been provided by

coquart and colleagues (2014). More recent studies have used the same incremental, two-step perceptually regulated protocol, as first proposed by Eston and thompson (1997), but extended the original scope of their protocol to include the theoretical terminal rPE of 20 to investigate the effi-cacy of rPE clamping for the direct assessment of VO2max (chidnok et al. 2013; Evans et al. 2013a; Mauger et al. 2013; Mauger and Sculthorpe 2012). With the exception of the study by chidnok et al. (2012) (who used rPE levels 8, 10, 12, 14, 16, 18, and 20), the same verbally anchored rPE levels have been used. Mauger and Sculthorpe (2012) used this procedure to compare against the VO2max from a standard ramp-incremented VO2max cycling protocol with 16 untrained subjects. Specifically, their protocol consisted of exercising for five, 2-min stages at rPE values of 11, 13, 15, 17, and 20, and was found to elicit a statistically significant 3 ml kg−1 min−1 higher VO2max. Mauger and colleagues (2013) followed-up this study using treadmill running as the exercise mode and found similar results that were consistent with their original study. these stud-ies seem promising with respect to improving the validity of VO2max assessment; however, two further studies found no significant difference in VO2max between cycling rPE-clamped and ramp-incremented protocols (chidnok et al. 2013; Evans et al. 2013a, b). the reasons for these con-flicting findings are unclear; differences between studies in exercise modality, and whether or not the durations of the rPE-clamped and ramp-incremented test protocols were similar within a given study, are plausible confounders when comparing studies. this latter point has been raised as a particularly important limitation to the interpretation of the results of the original study of Mauger and Sculthorpe (2012), as there was a 3-min difference in mean test dura-tion (Eston et al. 2012; chidnok et al. 2013). Although all of the studies indicate that an rPE-clamped VO2max test protocol is a valid method for VO2max determination, the conflicting findings of whether or not an rPE-clamped pro-tocol elicits higher VO2max values than a ramp-incremented protocol indicates that further research is required. Fur-thermore, when considering two equally valid exercise test protocols, an important consideration is whether one test is better tolerated by the test subject, which could have impli-cations for improved comfort and welfare of the subject, as well as improved adherence if repeated testing is required. Evans et al. (2013a, b) reported that the negative affect experienced during a ramp-incremented VO2max test was significantly reduced when using an rPE-clamped proto-col and suggested this was due to the autonomy provided by the self-pacing in the rPE-clamped protocol. conse-quently, the rPE-clamped protocol might be preferred by test subjects, but this has not been investigated.

given the controversy surrounding the efficacy of the rPE-clamped VO2max test protocol, the primary aim of

Eur J Appl Physiol

1 3

the present study was to compare the efficacy of ramp-incremented and rPE-clamped test protocols for eliciting VO2max in trained cyclists. A secondary aim was to inves-tigate whether individuals preferred one test over the other and, if so, whether they elicited higher VO2max values dur-ing their preferred test protocol. the study also compared the test–retest reliability of the two test protocols.

Methods

Subjects

twelve male and four female trained cyclists volun-teered to participate in this study. the males had the fol-lowing mean ± SD characteristics: age 33 ± 8 years; height 173 ± 7 cm; body mass 74.4 ± 8.8 kg; and BMI 24.8 ± 2.1 kg m2. the females had the follow-ing mean ± SD characteristics: age 38 ± 5 years; height 168 ± 4 cm; body mass 62.2 ± 4.0 kg; and BMI 22.1 ± 1.5 kg m2. Inclusion criteria required that sub-jects were aged between 18 and 45 years, non-smokers, free of any blood-borne diseases, free of injury for the past 6 months, and had spent a minimum of 6 h cycling per week for at least the past 6 months (lamberts et al. 2009). Subjects were excluded if they had cardiovascular disease, or cardiovascular disease risk factors, as indicated by a signed Physical Activity readiness Questionnaire (PAr-Q), or possessed a VO2max below the 60th percentile according to age and gender norms (AcSM 2010). During the study, the subjects spent 7.6 ± 3.0 h training on their bikes on 3–7 days week−1, and averaged approximately 121 ± 70 mi week−1, with the majority of their training completed on the road. Aside from biking, many subjects regularly engaged in resistance training, interval training, swimming, and running, and eight subjects were currently training for upcoming triathlons. the study was approved by the Marywood University Institutional review Board and all subjects provided written informed consent before undergoing any procedures.

Experimental overview

the present study utilized a randomized, completely coun-terbalanced, cross-over design to compare the efficacy of two exercise test protocols for eliciting VO2max. Each par-ticipant visited the laboratory on four occasions, which consisted of performing each VO2max test protocol twice (Fig. 1). the first attempt at each VO2max test protocol was regarded as familiarization. Subjects completed all four tests at the same time of day within a 2-week period, with a minimum of 48 h and a maximum of 96 h between tests. Subjects were instructed not to eat a large meal within 2 h

of testing, to refrain from consuming caffeine and alcohol 6 and 24 h before testing, respectively, and not to engage in any strenuous or unaccustomed exercise 24 h before test-ing. Subjects also were asked not to ride their bicycle to the laboratory for testing. On arrival to the laboratory on each visit, subjects were asked to sign a verification form stating that they had adhered to all pre-visit instructions.

At each visit, subjects were required to answer a series of questions to establish whether they were in a similar mental and physical state immediately before commencing the two different VO2max tests. the readiness and willing-ness to invest effort in each VO2max test were determined by measuring feelings of commitment and determination to exercise to the limit of exercise tolerance, perceived com-petence to continue exercising to achieve VO2max, and the level of intended effort. these variables were measured using visual analog scales that consisted of a horizontal 100-mm line on which the subjects marked their response. the extreme scores were anchored with the text ‘not at all/poor’ and ‘very much/excellent’. Subjects also rated their muscle soreness for nine areas of their body on a 10-point likert scale, where one was equivalent to ‘none’ and 10 was equivalent to ‘unbearable’. Muscle soreness was used as an indicator of muscle damage, as previous research has found that exercise-induced muscle damage (as indicated by increased muscle soreness and decreased peak torque development) increases perceived exertion and impairs

Fig. 1 Outline of study protocol. Eight subjects (solid arrows) began with the two ramp-incremented tests and verification tests in week 1 and then performed the two rPE-clamped tests in week 2. the other eight subjects (dashed arrows) began with the two rPE-clamped tests in week 1 and then performed the two ramp-incremented tests and verification tests in week 2. the first attempt at each test protocol was regarded as familiarization

Eur J Appl Physiol

1 3

physical performance (twist and Eston 2009). Preceding each VO2max test, subjects completed a 5-min standardized warm-up at 150 W for men and 100 W for women at a ped-aling cadence of 90 rPM. All VO2max tests were performed on a Velotron DynafitPro cycle ergometer (racerMate Inc., Seattle, WA, USA). During each test, rPM was the only performance measure that was not concealed from the sub-jects’ views on the digital output screen. Subjects were free to self-select and vary their pedal cadence throughout each trial, as lucia et al. (2006) reported that rPM does not affect VO2. chidnok et al. (2013) also reported that VO2max was not significantly different between ramp-incremented tests where pedal cadence was either fixed, or allowed to vary according to subject preference. Subjects were, how-ever, instructed not to allow their pedal cadence to drop below 80 rPM in all tests. Subjects were provided with continual verbal encouragement throughout all tests and a small fan set at a medium speed was used to help cool subjects during each test. Each subject’s height, body mass, and seat and handlebar positioning for cycling were meas-ured on arrival at the first visit to the laboratory.

rPE-clamped VO2max test

the rPE-clamped test protocol was a direct replication of that used by Mauger and Sculthorpe (2012). the test dura-tion was fixed at 10 min and consisted of five, 2-min stages, with each stage clamped at an rPE that was progressively increased with each stage: stage 1 = rPE 11 (‘light’); stage 2 = rPE 13 (‘somewhat hard’); stage 3 = rPE 15 (‘hard’); stage 4 = rPE 17 (‘very hard’); and stage 5 = rPE 20 (‘maximal exertion’). It was the subject’s responsibility to control his or her own work rate to maintain the pre-scribed rPE for each stage using a device mounted onto the handlebars of the cycle ergometer. Each time the ‘up’ or ‘down’ arrow on this device was tapped, cycling work rate increased or decreased, respectively, by 5 W; although subjects could not see the console to establish at which work rate they were working. Subjects were instructed to increase or decrease their work rate as frequently as was necessary to maintain the prescribed rPE throughout each stage and were given continual reminders of the rPE at which they should be working. Before each rPE-clamped test, subjects were given an explanation of the rPE scale and how they should use it for the test, using a modified version of the script used by Morris et al. (2009).

ramp-incremental VO2max test

the ramp-incremented test protocol involved standardized continuous increases in work rate that were automatically controlled by the Velotron coaching Software. the famil-iarization test began at 80 W and increased by 30 W min−1

for men and 20 W min−1 for women. the test was termi-nated when subjects could no longer pedal, or their cadence dropped below 80 rPM for more than 5 s. to control for time differences between the two test protocols, without jeopardizing the randomized order in which the subjects completed the tests, initial work rates and ramp rates were adjusted on an individual basis between the first and sec-ond ramp-incremented tests. For example, if a subject com-pleted his ramp-incremented familiarization test in 375 s with a POpeak of 267 W, in his second ramp-incremented test, the power output was increased by only 20 W min−1 rather than 30 W min−1, in order that he may achieve a similar POpeak in the desired 10-min test duration.

Measurement of power output, expired air, heart rate, blood lactate, and rPE

Power outputs for each VO2max test were recorded, saved, and exported to Excel using the ergometer software, and the highest value achieved during the test was regarded as POpeak. Minute ventilation and pulmonary gas exchange for the determination of VO2max, maximal minute ventilation (VEmax), and maximal respiratory exchange ratio (rErmax) were recorded continuously during the VO2max tests (Moxus System, AEI technologies Inc., Pittsburgh, PA, USA), as was heart rate for the determination of maximal heart rate (Hrmax) (Polar, S610, Kempele, Finland). All data were sub-sequently averaged over 15-s intervals and the highest 15-s average was regarded as the maximal value for that variable. A blood sample was collected via finger stick 1 min after the VO2max test, and was immediately analyzed for blood lactate concentration ([Bla]) with a lactate Plus handheld monitor (nova Biomedical, Waltham, MA, USA). Perceived exer-tion was recorded at the end of each stage of the ramp-incre-mented test protocol using Borg’s 6–20 Scale (Borg 1990).

Subjective test preference

After completing all four trials and before the investiga-tor disclosed any performance information, subjects were asked to indicate which of the two test protocols they pre-ferred performing: “now that you have completed both con-ditions, if you were to come into the Human Physiology lab on a regular basis throughout the year for VO2max test-ing, which test would you prefer to perform?”. Subjects’ responses, although allowed, were not restricted to a simple “ramp” or “clamp” answer, as subjects were prompted to explain why they preferred a particular test protocol.

Verification test

ten minutes after completing the ramp tests, sub-jects performed a supramaximal verification test

Eur J Appl Physiol

1 3

(Scharhag-rosenberger et al. 2011). this test began with subjects pedaling for 1 min at 60 % of the POpeak attained in the ramp test. Immediately following this first minute, the resistance was increased to 110 % POpeak and subjects were verbally encouraged to cycle until the limit of their exercise tolerance, or until the required pedal cadence could not be maintained (i.e., dropped below 80 rPM for more than 5 s).

Statistical analysis

Descriptive sample statistics are reported as the mean ± SD, unless otherwise stated. Mean differences in test duration, POpeak, and maximal physiological responses between the VO2max test protocols (second tests only) were compared using paired-samples t tests, as were the mean differences in VO2max in the second ramp-incremented test and associated verification test. A power calculation was conducted for the primary outcome measure of VO2max (g-Power software, Franz Faul, Universitat Kiel, germany) based on previously published test–retest variability data (Pivarnik et al. 1996) and a smallest worthwhile standard-ized effect of 0.75. A sample size of 16 provided 80 % power at an alpha of 0.05. the normality assumption for the differences in maximal rPE between VO2max test proto-cols was not plausible and, therefore, a nonparametric sign test for paired samples was used to analyses these data. A one sample t test, with a test value of zero, was used to assess whether the preferred test protocol elicited a higher VO2max than the non-preferred protocol. Systematic bias between the familiarization trial and the second trial for each test protocol was assessed using paired t tests. Meas-urement error for all of the dependent variables for both VO2max test protocols was calculated as the square root of the within-subjects error variance (i.e., the within-subjects SD) derived from a repeated measures AnOVA. reproduc-ibility was defined as 2.77 × the measurement error (Bland

and Altman 1996). Since the calculation of reproducibility may be considered too stringent, the smallest measureable difference is reported as half of the reproducibility (Hop-kins 2000). Differences in the readiness and willingness to invest effort and perceived muscle soreness between test protocols were analyzed using a t test and sign test, respec-tively. All statistical analyses were conducted using IBM SPSS Statistics 20 (SPSS Inc., chicago, Il, USA). two-tailed statistical significance was accepted as p < 0.05.

Results

the mean ± SD for each of the variables determined dur-ing the second ramp-incremented and rPE-clamped test protocols is shown in table 1. Mean power output and VO2 responses for both test protocols are shown in Fig. 2. the mean ± SD readiness and willingness to invest effort (averaged across commitment, competence, and intended effort) were 90 ± 6 in the second ramp-incremented pro-tocol and 90 ± 8 in the second rPE-clamped protocol and were not significantly different between protocols (mean difference = 0.09, 95 % cI = −2, 2; t = 0.9; p = 0.93). the median (interquartile range) perceived muscle sore-ness (averaged across the nine body locations) in the ramp-incremented and rPE-clamped protocols was 1.2 (0.3) and 1.0 (0.4), respectively, and also was not significantly differ-ent between protocols (p = 0.29).

test duration, POpeak and pedal cadence

test duration between the first (544 ± 97 s) and second (568 ± 72 s) ramp-incremented tests was significantly different (p < 0.05), but there was no significant differ-ence in test duration for the second ramp-incremented and rPE-clamped protocols (mean difference = 32 s; 95 % cI = −6, 71; t = 1.8; p = 0.091), or for POpeak (mean

Table 1 Mean ± SD (minimum–maximum) values for physical performance and maximal physiological responses during the ramp-incre-mented and rPE-clamped VO2max test protocols

POpeak peak power output, RPMaverage average pedaling cadence, VO2max maximal oxygen uptake, VEmax maximal minute ventilation, RERmax maximal respiratory exchange ratio, HRmax maximal heart rate, [BLa] post-test blood lactate concentration

ramp-incremented (n = 16) rPE-clamped (n = 16)

test duration (s) 568 ± 72 (480–711) 600 ± 0 –

POpeak (W) 330 ± 71 (239–436) 317 ± 97 (180–465)

rPMaverage 94 ± 4 (90–106) 97 ± 7 (91–114)

VO2max (l min−1) 3.86 ± 0.73 (2.81–5.12) 3.87 ± 0.72 (2.73–5.17)

VEmax (l min−1) 133.6 ± 22.9 (87.4–175.8) 133.8 ± 26.2 (84.6–181.2)

rErmax 1.10 ± 0.05 (1.01–1.20) 1.06 ± 0.07 (0.93–1.18)

Hrmax (beats min−1) 171 ± 12 (151–190) 172 ± 10 (151–187)

[Bla] (mmol l−1) 11.6 ± 2.0 (7.6–14.0) 12.0 ± 2.5 (9.0–17.8)

Eur J Appl Physiol

1 3

difference = 13 W; 95 % cI = −8, 35; t = 1.3; p = 0.21), or pedal cadence (mean difference = 3 rPM; 95 % cI = −1, 7; t = 1.8; p = 0.094).

Maximal physiological variables and rPEmax

the mean ± SD VO2max in the second ramp-incre-mented test (3.86 ± 0.73 l min−1) and the verification test (3.84 ± 0.68 l min−1) was not significantly differ-ent (mean difference = 0.02 l min−1; 95 % cI −0.07, 0.12; t = 0.5; p = 0.61). no significant differences between the second ramp-incremented and rPE-clamped test protocols were observed for VO2max (mean differ-ence = 0.002 l min−1; 95 % cI = −0.15, 0.15; t = 0.03; p = 0.97), VEmax (mean difference = 0.2 l min−1; 95 % cI = −7.9, 8.2; t = 0.04; p = 0.97), rErmax (mean dif-ference = 0.036; 95 % cI = −0.006, 0.08; t = 1.8;

p = 0.087), Hrmax (mean difference = 1 beat min−1; 95 % cI = −2, 4; t = 0.7; p = 0.51), or post-test [Bla] (mean difference = 0.4 mmol l−1; 95 % cI = −1.0, 1.7; t = 0.6; p = 0.58). However, a significant difference was observed for rPEmax (p = 0.001). the median (interquartile range) rPEmax attained in the ramp-incremented test protocol was 19 (1).

test–retest statistics

the mean difference (and associated 95 % cI), day-to-day variability, measurement error, reproducibility, and the smallest measureable difference for each dependent vari-able for each test protocol are shown in table 2. All the mean differences between the familiarization trial and sec-ond trial were below 5 % and non-significant (all p values ≥0.20). Day-to-day variability for VO2max was 4 and 3 % in the ramp-incremented and rPE-clamped test protocols, respectively. the two protocols had an identical measure-ment error (0.13 l min−1) and similar smallest measurable differences (ramp 0.19 l min−1; clamp 0.18 l min−1). Due to technical issues during five of the familiarization tests, test–retest reliability statistics for VO2max, VEmax, and rErmax are derived from only 11 subjects.

test protocol preference

Seven subjects preferred the ramp-incremented protocol and nine subjects preferred the rPE-clamped protocol. the VO2max attained in the preferred protocol was signifi-cantly higher than the non-preferred protocol (mean dif-ference = 0.14 l min−1; 95 % cI = 0.12, 0.27; t = 2.3; p = 0.034). A chi square test for independence, with a Yate’s continuity correction, indicated that this effect was not due to the test order of the protocols, as there was no association between protocol preference and test order (χ2 = 1.0, p = 0.32). Subjects typically stated that pref-erence for the ramp protocol was related to a lack of the need to ‘think’ during the test, whereas preference for the rPE-clamped protocol was typically because those sub-jects liked being able to have some control over the exer-cise intensity during the test.

Discussion

the primary aim of the present study was to compare the efficacy of ramp-incremented and rPE-clamped test pro-tocols for eliciting VO2max in trained cyclists. A secondary aim was to investigate whether individuals prefer one test over the other and, if so, whether they elicit higher VO2max values during their preferred test protocol. Another aim was to compare the day-to-day variability of the two tests. It

Fig. 2 the mean power output (a) and VO2 (b) in the ramp-incre-mented and rPE-clamped VO2max test protocols. the data points at the far right of the graphs show the mean (SD) maximal values attained during the tests. Data points between 480 and 600 s have been removed, since 480 s was the shortest test duration in the ramp-incremented protocol and loss of subjects in the calculation of the means thereafter distorted the trend in the data

Eur J Appl Physiol

1 3

was shown that both protocols elicited similar VO2max val-ues with the same day-to-day variability. It was also shown that the VO2max values were slightly higher in the preferred protocol. that is, those that “liked” or preferred the rPE-clamped protocol more than the ramp-incremental protocol elicited a slightly higher VO2max in the rPE-clamped proto-col, and vice versa.

Whereas the mean VO2max in the two protocols observed in the present study was almost identical and agrees with the findings of chidnok et al. (2013) and Evans et al. (2013a, b), Mauger and Sculthorpe (2012) and Mauger et al. (2013) observed a significant 3 ml kg−1 min−1 higher VO2max in an rPE-clamped test protocol as compared to a ramp-incremented protocol. Eston (2012) stated that the differences in VO2max observed by Mauger and Sculthorpe (2012) might be an artifact of the 3-min mean difference in test duration between their two protocols, a view that is consistent with an early study that reported VO2max was affected by differences in test duration (Buchfuhrer et al. 1983). this view also is consistent with the fact that no significant mean differences between test protocol dura-tion were observed in the present study, or the studies by chidnok et al. (2013) and Evans et al. (2013a, b); how-ever, most empirical evidence now suggests that VO2max is not affected by deviations in test duration such as the difference observed by Mauger and Sculthorpe (Midgley et al. 2008). As in their former study, Mauger et al. (2013) reported a significantly higher VO2max in the rPE-clamped protocol compared to the ramp-incremented protocol with no significant difference in mean test duration between protocols. However, it is important to note that since the

ramp-incremented protocol used a motorized treadmill and the rPE-clamped protocol used a non-motorized protocol, the interpretation of the results is confounded by ergometer type—an issue raised by the authors and others (Eston et al. 2014; Poole 2014)—and further research is required to establish whether motorized and non-motorized treadmills elicit different VO2max when matched for test protocol.

Although our observations reveal no significant dif-ferences in VO2max (or any other maximal physiological responses) between protocols, and this might appear to be a negative research finding, it does provide evidence that an rPE-clamped test protocol is a valid method of VO2max determination. the existing rPE-clamped protocol always lasts exactly 10 min and this is advantageous for busy exercise physiology laboratories with respect to schedul-ing tests. Future research could investigate the utility of an rPE-clamped protocol with a shorter fixed duration of 6 or 8 min to take further advantage of this characteristic of the test protocol. the rPE-clamped protocol also elimi-nates the need for the investigator to predict the maximal work rate to obtain a test duration that is appropriate for eliciting a true VO2max. A major limitation is that many important variables derived from ramp-incremented tests, such as the POpeak (Bentley et al. 2007), ventilatory thresh-old (Beaver et al. 1986), and the oxygen uptake efficiency slope (Antoine-Jonville et al. 2012), cannot be derived from rPE-clamped tests because these variables depend on a constant increase in work rate for their correct determina-tion and interpretation. the utility of the rPE-clamped test is, therefore, dependent on the specific requirements of the researcher or exercise physiology laboratory.

Table 2 test–retest reliability of physiological variables obtained at maximal exercise for the ramp-incremented and rPE-clamped VO2max tests

POpeak peak power output, VO2max maximal oxygen uptake, VEmax maximal minute ventilation, RERmax maximal respiratory exchange ratio, HRmax maximal heart rate, [BLa] post-test blood lactate concentration

Mean difference (95 % cI)

Day-to-day variability (%)

Measurement error

reproducibility Smallest measurable difference

ramp-incremented

POpeak (W) −2 (−9, 4) 3 9 24 12

VO2max (l min−1) −0.08 (−0.20, 0.05) 4 0.13 0.37 0.19

VEmax (l min−1) 2.3 (−3.9, 8.5) 5 6.5 18.0 9.0

rErmax 0.13 (−0.03, 0.05) 4 0.04 0.12 0.06

Hrmax (beats min−1) −1 (−5, 2) 3 4 12 6

[Bla] (mmol l−1) −0.5 (−1.5, 0.4) 10 1.0 2.8 1.4

rPE-clamped

POpeak (W) −2 (−29, 24) 11 35 96 48

VO2max (l min−1) 0.02 (−0.10, 0.14) 3 0.13 0.35 0.18

VEmax (l min−1) 3.8 (−4.4, 12.0) 6 8.7 24.0 12.0

rErmax 0.02 (−0.02, 0.07) 4 0.04 0.12 0.06

Hrmax (beats min−1) 1 (−2, 4) 2 4 10 5

[Bla] (mmol l−1) 0.03 (−1.2, 1.2) 15 1.5 4.3 2.1

Eur J Appl Physiol

1 3

the mean maximal rPE attained in the rPE-clamped protocol was significantly higher than in the ramp-incre-mented protocol, suggesting that, despite no differences in any maximal physiological response, the subjects, in gen-eral, perceived the rPE-clamped protocol as more physi-cally demanding. However, a limitation to the present study and previous studies (chidnok et al. 2013; Evans et al. 2013a; Mauger et al. 2013; Mauger and Sculthorpe 2012) is that it has not been confirmed that subjects actually reached an rPE of 20 in the final stage of the rPE-clamped protocol, which is a key aspect of the rPE-clamped proto-col. Subjects are asked to provide a maximal effort in incre-mental VO2max test protocols, but often report rPE values below 20 at the end of the test (Andreacci et al. 2002; Eston et al. 2007; Faulkner and Eston 2007; Wood et al. 2010), as was the case in the present study. It is plausible that the same is true for the rPE-clamped protocol, and further research is needed to explore this issue.

Subjects obtained a statistically significant 4 % higher VO2max in their preferred test protocol as compared to their non-preferred protocol, suggesting that using a preferred test protocol may elicit a higher VO2max. Another plausible explanation for this finding is that subjects preferred the test protocol in which they perceived they performed best (for example, because they felt less mentally or physically fatigued before the test that day), which could be inde-pendent of the characteristics of the test protocol. Subjects typically rationalized their preference for the ramp protocol as not needing to ‘think’ during the test, whereas prefer-ence for the rPE-clamped protocol was typically because subjects liked being able to have some control over the exercise intensity throughout the test. Using a preferred protocol may serve as an advantage for researchers and clinicians, as it may improve adherence and compliance to testing procedures, if involved in repeated testing, such as during an intervention study, continuing sport science sup-port, or repeated clinical investigation. Another issue is that the observed improvement in VO2max is below the smallest measureable difference of ~180 ml min−1, which suggests that the slight 4 % increase in VO2max with the preferred protocol may not be physiologically meaningful. caution is warranted when interpreting the finding that VO2max was increased when subjects performed their preferred proto-col, and future research involving rPE-clamped VO2max test protocols could investigate this issue further, particu-larly whether personality or competitive style affects per-formance or enjoyment of one type of test protocol over the other.

the day-to-day variability of VO2max and other physio-logical variables derived from ramp-incremented and step-incremented test protocols have been well established (e.g., Harling et al. 2003; Katch et al. 1982). the present study shows that the day-to-day variability of VO2max and other

physiological variables derived from an rPE-clamped test protocol are similar to that of a ramp-incremented proto-col. there was no systematic bias between the familiariza-tion and second test for any variables in the rPE-clamped protocol, demonstrating that a familiarization session is not required to obtain valid test results.

Conclusion

the rPE-clamped test protocol was as effective as the ramp-incremented protocol for eliciting VO2max, and dem-onstrated similar test–retest reliability and should be con-sidered as a valid alternative protocol, particularly where a fixed test duration is desirable. the findings of no dif-ferences in VO2max are consistent with the observations of chidnok et al. 2013 and Evans et al. 2013a, b. Future research needs to be conducted to evaluate the efficacy of different rPE-clamped protocols using different modes of exercise and various populations. Although VO2max is an important measure of cardiorespiratory fitness, the valid-ity of other important measures of cardiorespiratory fitness, such as the ventilatory threshold and the oxygen uptake efficiency slope, as well as POpeak, also should be consid-ered when using or developing alternative test protocols.

Acknowledgments this project was funded by the Marywood Uni-versity graduate research and creative Projects Fund. the authors of this study would like to especially thank Kathy Uhranowsky, along with graduate assistants Kaleen lavin and nicholas Fiolo, for their assistance during data collection.

Conflict of interest there are no conflicts of interest to report.

References

AcSM (2010) AcSM’s guidelines for exercise testing and prescrip-tion. lippincott Williams & Wilkins, Philadelphia

Al-rahamneh HQ, Eston rg (2011) the validity of predicting peak oxygen uptake from a perceptually guided graded exercise test during arm exercise in paraplegic individuals. Spinal cord 49(3):430–434. doi:10.1038/sc.2010.139

Andreacci Jl, leMura lM, cohen Sl, Urbansky EA, chelland SA, Von Duvillard SP (2002) the effects of frequency of encourage-ment on performance during maximal exercise testing. J Sports Sci 20(4):345–352. doi:10.1080/026404102753576125

Antoine-Jonville S, Pichon A, Vazir A, Polkey MI, Dayer MJ (2012) Oxygen uptake efficiency slope, aerobic fitness, and V(E)-VcO2 slope in heart failure. Med Sci Sports Exerc 44(3):428–434. doi:10.1249/MSS.0b013e31822f8427

Arena r, Sietsema KE (2011) cardiopulmonary exercise testing in the clinical evaluation of patients with heart and lung dis-ease. circulation 123(6):668–680. doi:10.1161/cIrcUlAtIOnAHA.109.914788

Beaver Wl, Wasserman K, Whipp BJ (1986) A new method for detecting anaerobic threshold by gas exchange. J Appl Physiol 60(6):2020–2027

Eur J Appl Physiol

1 3

Bentley DJ, newell J, Bishop D (2007) Incremental exercise test design and analysis: implications for performance diagnostics in endurance athletes. Sports Med 37(7):575–586 (pii: 3772)

Bhambhani Y, Singh M (1985) the effects of three training intensities on VO2max and VE/VO2 ratio. can J Appl Sport Sci 10(1):44–51

Bland JM, Altman Dg (1996) Measurement error. Br Med J 313(7059):744

Borg g (1990) Psychophysical scaling with applications in physi-cal work and the perception of exertion. Scand J Work Environ Health 16(Suppl 1):55–58

Buchfuhrer MJ, Hansen JE, robinson tE, Sue DY, Wasserman K, Whipp BJ (1983) Optimizing the exercise protocol for cardiopul-monary assessment. J Appl Physiol respir Environ Exerc Physiol 55(5):1558–1564

chidnok W, DiMenna FJ, Bailey SJ, Vanhatalo A, Morton rH, Wilkerson DP, Jones AM (2012) Exercise tolerance in intermit-tent cycling: Application of the critical power concept. Med Sci Sports Exerc 44:966–976

chidnok W, Dimenna FJ, Bailey SJ, Burnley M, Wilkerson DP, Van-hatalo A, Jones AM (2013) VO2max is not altered by self-pacing during incremental exercise. Eur J Appl Physiol 113(2):529–539. doi:10.1007/s00421-012-2478-6

coquart JB, garcin M, Parfitt g, tourny-chollet c, Eston rg (2014) Prediction of maximal or peak oxygen uptake from ratings of perceived exertion. Sports Med. doi:10.1007/s40279-013-0139-5

Day Jr, rossiter HB, coats EM, Skasick A, Whipp BJ (2003) the maximally attainable VO2 during exercise in humans: the peak vs. maximum issue. J Appl Physiol 95(5):1901–1907. doi:10.1152/japplphysiol.00024.2003

Eston rg, thompson M (1997) Use of ratings of perceived exertion for predicting maximal work rate and prescribing exercise inten-sity in patients taking atenolol. Br J Sports Med 31(2):114–119

Eston rg, lamb Kl, Parfitt g, King n (2005) the validity of predict-ing maximal oxygen uptake from a perceptually-regulated graded exercise test. Eur J Appl Physiol 94(3):221–227. doi:10.1007/s00421-005-1327-2

Eston rg, Faulkner JA, Mason EA, Parfitt g (2006) the validity of predicting maximal oxygen uptake from perceptually regulated graded exercise tests of different durations. Eur J Appl Physiol 97(5):535–541. doi:10.1007/s00421-006-0213-x

Eston r, Faulkner J, St clair gibson A, noakes t, Parfitt g (2007) the effect of antecedent fatiguing activity on the relationship between perceived exertion and physiological activity during a constant load exercise task. Psychophysiology 44(5):779–786. doi:10.1111/j.1469-8986.2007.00558.x

Eston r, lambrick D, Sheppard K, Parfitt g (2008) Prediction of maximal oxygen uptake in sedentary males from a perceptu-ally regulated, sub-maximal graded exercise test. J Sports Sci 26(2):131–139. doi:10.1080/02640410701371364

Eston r, Evans H, Faulkner J, lambrick D, Al-rahamneh H, Parfitt g (2012) A perceptually regulated, graded exercise test predicts peak oxygen uptake during treadmill exercise in active and sed-entary participants. Eur J Appl Physiol 112(10):3459–3468. doi:10.1007/s00421-012-2326-8

Eston rg, crockett A, Jones AM (2014) Discussion of “the efficacy of the self-paced V̇O2max test to measure maximal oxygen uptake in treadmill running” 1. Appl Phys nutr Metab 39(1–2). doi:10.1139/apnm-2013-0501

Evans H, Parfitt g, Eston r (2013a) Use of a perceptually-regulated test to measure maximal oxygen uptake is valid and feels better. Eur J Sport Sci. doi:10.1080/17461391.2013.832804

Evans HJ, Parfitt g, Eston rg (2013b) the perceptually regu-lated exercise test is sensitive to increases in maximal oxygen uptake. Eur J Appl Physiol 113(5):1233–1239. doi:10.1007/s00421-012-2541-3

Faulkner J, Eston r (2007) Overall and peripheral ratings of per-ceived exertion during a graded exercise test to volitional exhaus-tion in individuals of high and low fitness. Eur J Appl Physiol 101(5):613–620. doi:10.1007/s00421-007-0536-2

Faulkner J, Parfitt g, Eston r (2007) Prediction of maximal oxygen uptake from the ratings of perceived exertion and heart rate dur-ing a perceptually-regulated sub-maximal exercise test in active and sedentary participants. Eur J Appl Physiol 101(3):397–407. doi:10.1007/s00421-007-0508-6

Harling SA, tong rJ, Mickleborough tD (2003) the oxygen uptake response running to exhaustion at peak treadmill speed. Med Sci Sports Exerc 35(4):663–668. doi:10.1249/01.MSS.0000058434.53664.Ec

Hill AV, lupton H (1923) Muscular exercise, lactic acid, and the sup-ply and utilization of oxygen. Q J Med 16:135–171

Hopkins Wg (2000) Measures of reliability in sports medicine and science. Sports Med 30(1):1–15

Katch Vl, Sady SS, Freedson P (1982) Biological variability in maxi-mum aerobic power. Med Sci Sports Exerc 14(1):21–25

lamberts rP, Swart J, Woolrich rW, noake tD, lambert MI (2009) Measurement error associated with performance testing in well-trained cyclists: application to the precision of monitoring changes in training status. Int Sport Med J 10(1):33–44

lucia A, rabadan M, Hoyos J, Hernandez-capilla M, Perez M, San Juan AF, Earnest cP, chicharro Jl (2006) Frequency of the VO2max plateau phenomenon in world-class cyclists. Int J Sports Med 27(12):984–992. doi:10.1055/s-2006-923833

Macfarlane DJ (2001) Automated metabolic gas analysis systems: a review. Sports Med 31(12):841–861

Mauger Ar, Sculthorpe n (2012) A new VO(2)max protocol allowing self-pacing in maximal incremental exercise. Br J Sports Med 46(1):59–63. doi:10.1136/bjsports-2011-090006

Mauger Ar, Metcalfe AJ, taylor l, castle Pc (2013) the efficacy of the self-paced VO2max test to measure maximal oxygen uptake in treadmill running. Appl Physiol nutr Metab 38(12):1211–1216. doi:10.1139/apnm-2012-0384

Midgley AW, Mcnaughton lr, Wilkinson M (2006) Is there an opti-mal training intensity for enhancing the maximal oxygen uptake of distance runners?: empirical research findings, current opin-ions, physiological rationale and practical recommendations. Sports Med 36(2):117–132

Midgley AW, Bentley DJ, luttikholt H, Mcnaughton lr, Mil-let gP (2008) challenging a dogma of exercise physiology: does an incremental exercise test for valid VO2max determina-tion really need to last between 8 and 12 minutes? Sports Med 38(6):441–447

Morris M, lamb K, cotterrell D, Buckley J (2009) Predicting maxi-mal oxygen uptake via a perceptually regulated exercise test (PrEt). J Exerc Sci Fit 7(2):122–128

Morris M, lamb Kl, Hayton J, cotterrell D, Buckley J (2010) the validity and reliability of predicting maximal oxygen uptake from a treadmill-based sub-maximal perceptually regulated exercise test. Eur J Appl Physiol 109(5):983–988. doi:10.1007/s00421-010-1439-1

noakes tD (2008) testing for maximum oxygen consumption has produced a brainless model of human exercise performance. Br J Sports Med 42(7):551–555. doi:10.1136/bjsm.2008.046821

Pivarnik JM, Dwyer Mc, lauderdale MA (1996) the reliability of aerobic capacity (VO2max) testing in adolescent girls. res Q Exerc Sport 67(3):345–348

Poole Dc (2014) Discussion: “the efficacy of the self-paced V̇O2max test to measure maximal oxygen uptake in treadmill running” 1. Appl Physiol nutr Metab 39(1–3). doi:10.1139/apnm-2013-0549

Scharhag-rosenberger F, carlsohn A, cassel M, Mayer F, Scharhag J (2011) How to test maximal oxygen uptake: a study on timing

Eur J Appl Physiol

1 3

and testing procedure of a supramaximal verification test. Appl Physiol nutr Metab 36(1):153–160. doi:10.1139/H10-099

Struthers r, Erasmus P, Holmes K, Warman P, collingwood A, Sneyd Jr (2008) Assessing fitness for surgery: a comparison of ques-tionnaire, incremental shuttle walk, and cardiopulmonary exer-cise testing in general surgical patients. Br J Anaesth 101(6):774–780. doi:10.1093/bja/aen310

twist c, Eston rg (2009) the effect of exercise-induced mus-cle damage on perceived exertion and cycling endurance

performance. Eur J Appl Physiol 105(4):559–567. doi:10.1007/s00421-008-0935-z

Wood rE, Hills AP, Hunter gr, King nA, Byrne nM (2010) VO2max in overweight and obese adults: do they meet the threshold crite-ria? Med Sci Sports Exerc 42(3):470–477. doi:10.1249/MSS.0b013e3181b666ad