Measurement of a True V˙O2max during a Ramp Incremental Test Is Not Confirmed by a Verification Phase

Abstract

The accuracy of an exhaustive ramp incremental (RI) test to determine maximal oxygen uptake (V˙O2max) was recently questioned and the utilization of a verification phase proposed as a gold standard. This study compared the oxygen uptake (V˙O2) during a RI test to that obtained during a verification phase aimed to confirm attainment of V˙O2max. Sixty-one healthy males [31 older (O) 65 ± 5 yrs; 30 younger (Y) 25 ± 4 yrs] performed a RI test (15–20 W/min for O and 25 W/min for Y). At the end of the RI test, a 5-min recovery period was followed by a verification phase of constant load cycling to fatigue at either 85% (n = 16) or 105% (n = 45) of the peak power output obtained from the RI test. The highest V˙O2 after the RI test (39.8 ± 11.5 mL·kg⁻¹·min⁻¹) and the verification phase (40.1 ± 11.2 mL·kg⁻¹·min⁻¹) were not different (p = 0.33) and they were highly correlated (r = 0.99; p < 0.01). This response was not affected by age or intensity of the verification phase. The Bland-Altman analysis revealed a very small absolute bias (−0.25 mL·kg⁻¹·min⁻¹, not different from 0) and a precision of ±1.56 mL·kg⁻¹·min⁻¹ between measures. This study indicated that a verification phase does not highlight an under-estimation of V˙O2max derived from a RI test, in a large and heterogeneous group of healthy younger and older men naïve to laboratory testing procedures. Moreover, only minor within-individual differences were observed between the maximal V˙O2 elicited during the RI and the verification phase. Thus a verification phase does not add any validation of the determination of a V˙O2max. Therefore, the recommendation that a verification phase should become a gold standard procedure, although initially appealing, is not supported by the experimental data.

Full text

ORIGINAL RESEARCH
published: 27 February 2018
doi: 10.3389/fphys.2018.00143
Frontiers in Physiology | www.frontiersin.org 1February 2018 | Volume 9 | Article 143
Edited by:
Billy Sperlich,
University of Würzburg, Germany
Reviewed by:
Fabio Esposito,
Università degli Studi di Milano, Italy
Carolin Stangier,
German Sport University Cologne,
Germany
*Correspondence:
Juan M. Murias
jmmurias@ucalgary.ca
Specialty section:
This article was submitted to
Exercise Physiology,
a section of the journal
Frontiers in Physiology
Received: 30 June 2017
Accepted: 12 February 2018
Published: 27 February 2018
Citation:
Murias JM, Pogliaghi S and
Paterson DH (2018) Measurement of
a True ˙
VO2max during a Ramp
Incremental Test Is Not Confirmed by
a Verification Phase.
Front. Physiol. 9:143.
doi: 10.3389/fphys.2018.00143
Measurement of a True ˙
VO2max
during a Ramp Incremental Test Is
Not Confirmed by a Verification
Phase
Juan M. Murias 1
*, Silvia Pogliaghi 2and Donald H. Paterson 3
1Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada, 2Department of Neurosciences, Biomedicine and
Movement Sciences, University of Verona, Verona, Italy, 3School of Kinesiology, The University of Western Ontario, London,
ON, Canada
The accuracy of an exhaustive ramp incremental (RI) test to determine maximal oxygen
uptake ( ˙
VO2max) was recently questioned and the utilization of a verification phase
proposed as a gold standard. This study compared the oxygen uptake ( ˙
VO2) during
a RI test to that obtained during a verification phase aimed to confirm attainment of
˙
VO2max. Sixty-one healthy males [31 older (O) 65 ±5 yrs; 30 younger (Y) 25 ±4 yrs]
performed a RI test (15–20 W/min for O and 25 W/min for Y). At the end of the RI test,
a 5-min recovery period was followed by a verification phase of constant load cycling
to fatigue at either 85% (n=16) or 105% (n=45) of the peak power output obtained
from the RI test. The highest ˙
VO2after the RI test (39.8 ±11.5 mL·kg−1·min−1) and
the verification phase (40.1 ±11.2 mL·kg−1·min−1) were not different (p=0.33) and
they were highly correlated (r=0.99; p<0.01). This response was not affected by
age or intensity of the verification phase. The Bland-Altman analysis revealed a very
small absolute bias (−0.25 mL·kg−1·min−1, not different from 0) and a precision of
±1.56 mL·kg−1·min−1between measures. This study indicated that a verification phase
does not highlight an under-estimation of ˙
VO2max derived from a RI test, in a large
and heterogeneous group of healthy younger and older men naïve to laboratory testing
procedures. Moreover, only minor within-individual differences were observed between
the maximal ˙
VO2elicited during the RI and the verification phase. Thus a verification
phase does not add any validation of the determination of a ˙
VO2max. Therefore, the
recommendation that a verification phase should become a gold standard procedure,
although initially appealing, is not supported by the experimental data.
Keywords: maximal oxygen uptake, oxidative metabolism, exercise testing, aerobic performance, aging
INTRODUCTION
Exercise physiologists have been interested in the measurements of oxygen uptake ( ˙
VO2)
and maximal ˙
VO2(˙
VO2max) since early in the 20th century (Krogh and Lindhard, 1913;
Hill and Lupton, 1923). Given the importance of ˙
VO2max as an integrative measure
of different components of the cardiovascular and neuromuscular system to exercise, its
measurement has been widespread not only as an indicator of human performance (Hoppeler
and Weibel, 2000; di Prampero, 2003; Levine, 2008), but also as a marker of overall
cardiovascular and cardiorespiratory function in different healthy and clinical populations

Murias et al. Verification Does Not Verify ˙
VO2max
(Frontera et al., 1990; Borrelli et al., 2003; Pogliaghi et al.,
2006; Levine, 2008; Paterson and Warburton, 2010; Jensen et al.,
2016) and different environmental conditions (Bringard et al.,
2010; Doria et al., 2011). Similarly, measures of ˙
VO2max have
been used to determine the efficacy of different exercise training
interventions aimed at improving physiological function both
from performance as well as health perspectives (Pogliaghi et al.,
2006; Murias et al., 2010a; Bruseghini et al., 2015). Considering
the importance of ˙
VO2max for assessment of performance and
health, adequate protocols capable of establishing a true maximal
value are needed to provide confidence for evaluation and
longitudinal follow-up.
Early studies measuring expired gases and volumes from
a Douglas bag promoted the use of testing protocols that
required prolonged steps of progressively increased intensity;
such protocols aimed to establish a steady-state or sustainable
response in each step, until critical intensities of exercise
prevented further steps from being completed (ÅSTRAND, 1960;
Glassford et al., 1965). Under those conditions, a work rate (or
speed) of exercise that resulted in no further increase in ˙
VO2
despite the increase in energy demand was established and this
plateau response was considered a true ˙
VO2max, as proposed
by Taylor et al. (1955). With the development of fast-response
breath-by-breath gas exchange and volume analyzers, researchers
started to move away from these types of time-consuming
protocols (Buchfuhrer et al., 1983), and step incremental and
ramp incremental (RI) tests became widely used to measure the
˙
VO2max response during exercise to exhaustion. RI protocols
allow for rapid determination of ˙
VO2max as well as other valuable
indexes such as the exercise intensity thresholds; however,
some researchers have questioned the accuracy of RI tests
to consistently provide a true ˙
VO2max value as a plateau in
˙
VO2is not always (or seldom) observed (Rossiter et al., 2006;
Poole et al., 2008; Poole and Jones, 2017). To circumvent this
limitation, secondary criteria such as an increase in blood lactate
concentration [La] above 8 mmol·L−1, a heart rate response
within 10 beats per minute (bpm) of the maximal predicted
value, a respiratory exchange ratio (RER) higher than 1.10, and
a rating of perceived exertion (RPE) >18, are commonly used
to establish the attainment of a true ˙
VO2max response (ACSM,
2003). However, as indicated by Midgley et al. (2007) and Poole
et al. (2008), secondary criteria do not seem valid for accurate
determination of the attainment of ˙
VO2max.
Another approach to establish the attainment of ˙
VO2max
consists of executing a verification (or validation) phase
subsequent to the RI test (Day et al., 2003; Midgley and Carroll,
2009). Although the exact origin of this model is not clearly
established (Midgley and Carroll, 2009), Rossiter et al. (2006)
proposed that, following a recovery period of five minutes
subsequent to the RI test, a constant load exercise to exhaustion
should be performed at either 95 or 105% of the peak power
output (PO) obtained during the RI test. The use of a verification
phase to confirm the attainment of a true maximum during a RI
test in which a plateau in ˙
VO2may not be present, is based on the
following assumptions:
(i) a RI test may fail to provide a true ˙
VO2max; (ii) an upper
limit to ˙
VO2exists and this value can only be underestimated
but not overestimated; (iii) during a constant load exercise to
the limit of tolerance in the very heavy/severe domain, ˙
VO2will
project to ˙
VO2max within the time of task failure. Therefore,
according to Rossiter et al. (2006), the lack of significant
differences in the ˙
VO2response of the constant load verification
phase, both at 95 and 105% of peak PO, compared to the highest
˙
VO2observed during the RI test, would provide the objective
“plateau criterion” that often remains elusive during a RI test
and confirm that a maximal value was obtained. Importantly,
this protocol not only corroborated the presence of an upper
limit of the ˙
VO2response, but it also indicated that the highest
˙
VO2values obtained during a RI were not different from those
observed during the verification phase and likely reflected the
achievement of a true ˙
VO2max.
Recently, a review by Poole and Jones (2017) proposed
the idea that the denomination of “peak” ˙
VO2(˙
VO2peak) is
no longer acceptable and that validated ˙
VO2max results, as
derived from a verification phase, should be presented in
all future studies. An important point raised by Poole and
Jones (2017) is that even though the RI test might yield
a highly reproducible ˙
VO2max response in active or trained
participants who are accustomed to pushing themselves to
exhaustion, this may not be the case with less experienced,
unmotivated, and/or clinical populations. Thus, even though a
RI test might provide a trustable measure of ˙
VO2max in trained
individuals, a verification phase should always be performed in
any population unaccustomed to pushing to the upper limits of
tolerance.
Although the verification phase appears appealing in
providing a strategy to overcome the ongoing ˙
VO2max-peak
debate, data from different studies do not convincingly support
the usefulness or necessity of a verification phase either in the
general healthy population or in specific clinical/frail/unfit
populations. In sedentary (Astorino et al., 2009), recreationally
active (Sedgeman et al., 2013; Nolan et al., 2014), overweight
and obese (Wood et al., 2010; Sawyer et al., 2015) adults, as well
as children (Barker et al., 2011), the ˙
VO2response during the
verification phase was not higher than that observed during the
RI test. This was also the case in a group of chronic heart failure
patients (Bowen et al., 2012). These data could suggest that the
verification phase provided a confirmation that a true ˙
VO2max
was established in these subjects. However, these very same
findings could just as plausibly indicate that the RI test per-se
was an adequate protocol, yielding a true maximal response in
most participants. Moreover, a recent study has shown that a
verification phase resulted in a lower ˙
VO2value as compared
to that observed during a graded incremental test (McGawley,
2017). Importantly, the possible usefulness of a verification phase
has only been investigated in relatively small and homogeneous
samples and (with the exception of McGawley (2017)) with a
suboptimal statistical approach (i.e., only comparison of mean
values). Additionally, healthy older adults, for whom ˙
VO2max
is the strongest predictor of independent living (Paterson and
Warburton, 2010) and for whom a verification phase would
theoretically be needed for accurate ˙
VO2max determination
(Poole and Jones, 2017), have never previously been evaluated.
Establishing if a verification phase actually adds confidence in the
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Murias et al. Verification Does Not Verify ˙
VO2max
achievement of ˙
VO2max in this population would contribute to
further support or oppose the recommendation of such practice.
Poole and Jones (2017) recommended that the verification
phase should be performed at intensities exceeding the peak
PO obtained at the end of the RI test (e.g., 105% of peak PO).
This is proposed in order to satisfy the plateau criterion (i.e.,
no further increase in ˙
VO2despite the increase in PO) that is
the foundation of the ˙
VO2max concept. However, it should be
noted that, due to the presence of the so called slow component
of ˙
VO2, any constant load PO above critical power will result in
the achievement of ˙
VO2max, provided that time to task failure is
sufficiently prolonged (Poole and Jones, 2012). This well-known
physiological phenomenon provides the rationale for using
workloads that are not only above but also below maximal PO for
the verification phase (Rossiter et al., 2006), with lower intensities
possibly favoring compliance and reducing the risk associated to
supramaximal exercise in older or clinical populations. Indeed,
verification phases conducted at a submaximal PO yield ˙
VO2max
values not different from those obtained from RI tests (Rossiter
et al., 2006; Sedgeman et al., 2013).
Thus, given the uncertainties related to the ability of
establishing ˙
VO2max during a RI test, and the proposal that a
verification phase with constant load might confirm the RI ˙
VO2
or identify that the RI test was not maximal, the goals of this study
were to: (1) determine whether a constant load verification phase
yields a ˙
VO2higher than the RI test; (2) examine the variation of
the differences around the mean between the highest ˙
VO2of the
RI test and the verification phase; (3) determine the role of age
group (i.e., younger vs. older adults) on the possible difference in
the ˙
VO2value between the RI test and the verification phase; (4)
determine the role of the intensity of the verification phase (i.e.,
above or below the PO elicited at the end of the RI test) on the
possible difference between the ˙
VO2value during the RI test and
the verification phase. We tested the hypothesis that a verification
phase (either below or above the end-RI intensity) would produce
a higher ˙
VO2than that observed during the RI test.
MATERIALS AND METHODS
This study combines sets of data collected in two different
locations: The University of Western Ontario and the University
of Verona. Although part of the ˙
VO2max data have been reported
elsewhere (Murias et al., 2010b, 2011; Bruseghini et al., 2015; Keir
et al., 2015) this is the first time that the ˙
VO2data derived from
the RI test and verification phase have been reported together and
compared.
Participants
Data from a total of 61 healthy males (30 younger, Y: 25 ±4 yr;
178 ±6 cm; 79 ±13 kg and 31 older adults O: 68 ±5 yr; 174
±8 cm; 78 ±10 kg; mean ±SD) were included in the present
analysis. Eight younger and eight older adults performed the
testing procedures at The University of Western Ontario (RI test
+verification phase at 85% of peak PO at the end of the RI test).
The remaining 22 younger and 23 older adults were tested at the
University of Verona (RI test +verification phase at 105% of peak
PO at the end of the RI test). All participants were volunteers and
provided written informed consent to participate in the study.
Participants were included in this database if they were aged
between 18 and 90 years old, had performed a RI test and a
subsequent verification phase, were relatively naïve to laboratory
testing procedures (i.e., had not been involved in laboratory
testing in at least the previous 12 months). All participants
were recreationally active, community dwelling individuals, none
of whom was involved in an organized endurance training
regime when the original testing took place. Common exclusion
criteria were obesity (body mass index >30 kg/m2), smoking,
involvement in any endurance training program within the
previous twelve months, taking medications that would affect
the cardiorespiratory or hemodynamic responses to exercise,
or a history of cardiovascular, respiratory or musculoskeletal
diseases. All subjects completed a PAR-Q+questionnaire prior
to enrolment and all older adults were medically screened
by a physician before being accepted into the study. All
procedures were approved by The University of Western Ontario
Research Ethics Board for Health Sciences Research Involving
Human Subjects or by the Ethics Board of the Department
of Neurosciences, Biomedicine and Movement Sciences at the
University of Verona.
Protocol
Participants performed a maximal RI test from a baseline of 20 W
to the PO that elicited exhaustion using increments of 25 W/min
(Y) and 15–20 W/min (O). Based on the anticipated fitness level
of O (Pogliaghi et al., 2014) a ramp slope (i.e., W/min increment)
was chosen that would bring the participants to exhaustion
within 10–12 min based on the ACSM (2003) guidelines. The
RI test was performed on a cycle ergometer (Lode Corival
400; Lode B.V., Groningen, Holland) and ˙
VO2was measured
throughout the test. After completion of the RI test, participants
returned to cycling at the baseline PO of 20 W for 5 min, after
which an instantaneous step increase in the PO was applied and
the participants performed a constant load cycling exercise to
volitional fatigue at a power output calculated to be either 85%
(n=16) or 105% (n=45) of the peak PO achieved during
the RI test. A similar approach has been previously described to
assess a “true” plateau in the ˙
VO2response and thus confirm
the attainment of a true ˙
VO2max (Sedgeman et al., 2013). By
reducing the relative exercise intensity, the goal in this case was
to obtain a longer time to exhaustion, in turn allowing sufficient
time for a ˙
VO2max to be achieved. The highest ˙
VO2from each test
was defined as the greatest consecutive 20-s average during each
exhaustive test.
Measurements
Gas-exchange measurements at the University of Western
Ontario were conducted as previously described (Babcock et al.,
1994). Briefly, inspired and expired flow rates were measured
using a low dead space (90 mL) bidirectional turbine (Alpha
Technologies VMM 110) which was calibrated before tests
using a syringe of known volume. Inspired and expired gases
were sampled continuously (every 20 ms) at the mouth and
analyzed for concentrations of O2, CO2, and nitrogen (N2) by
mass spectrometry (Perkin Elmer MGA-1100) after calibration
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Murias et al. Verification Does Not Verify ˙
VO2max
with precision-analyzed gas mixtures. Breath-by-breath alveolar
gas exchange was calculated using the algorithms of Beaver
et al. (1981). Heart rate (HR) was monitored continuously by
a three-lead arrangement electrocardiogram using PowerLab
(ML132/ML880; ADInstruments, Colorado Springs, CO). Data
were recorded using LabChart v4.2 (ADInstruments, Colorado
Springs, CO) on a separate computer.
At the University of Verona, breath-by-breath gas exchange
and ventilation were continuously measured using a metabolic
cart (QuarkB2; COSMED, Rome, Italy) as previously described
(Keir et al., 2015). The gas analyzers were calibrated before each
experiment using a gas mixture of known concentration, and
the turbine flowmeter was calibrated using a 3-L syringe (Hans
Rudolph, Inc.). HR data were collected using radiotelemetry
(SP0180 Polar Transmitter; Polar Electro, Inc., Kempele,
Finland) and calculated over the duration of each breath.
Statistics
All statistics were performed using SPSS version 23 (SPSS,
Chicago, IL). Data are presented as means ±SD. After ensuring
the normal distribution of the data (Shapiro–Wilk test), and
equality of variance for the 85% and 105% groups (Levene’s
test) a three-way repeated-measures ANOVA was used to test
the possible influence and interactions of test type (RI test
vs. constant load verification phase), age subgroup (Y vs. O)
and verification phase intensity (85% vs. 105%) on the highest
measures of ˙
VO2observed during the tests. Significant main
effects and interactions were analyzed using the Bonferroni
post-hoc test. Based on a power calculation, 49 participants
were required to identify significant differences between groups
for detecting changes larger than our estimated measurement
error (i.e., 2 mL·kg−1·min−1) with a statistical power >0.8.
The correlation between the highest ˙
VO2during the RI test
and the constant load verification phase was assessed by
Pearson’s product moment correlation coefficient. Furthermore,
the individual difference between ˙
VO2observed during the
RI test the constant load verification phase was calculated in
absolute units (absolute bias in mL·kg−1·min−1) and as a percent
of RI ˙
VO2(% bias). Bland-Altman plots, followed by a one-
sample z-test (Bland and Altman, 1986), were used to determine
average bias, precision (i.e., standard deviation of the differences
between measures) and limits of agreement between the ˙
VO2
measures. The number and percent of subjects in which the RI
test either overestimated or underestimated ˙
VO2max compared
to the verification phase by over 2 mL·kg−1·min−1(equal to the
minimum detectable change as measured in our laboratories for
˙
VO2measures between 2.1 and 3.5 L·min−1) (Keir et al., 2014,
2015) was calculated. For all comparisons, statistical significance
was declared when P<0.05.
RESULTS
The peak PO was significantly lower in O (198 ±35 W) compared
to Y (339 ±54 W; P=0.86). Time to exhaustion during the
RI test was shorter in O (10.2 ±2.3 min; range 7.9–18.8 min)
compared to Y (12.8 ±2.0 min; range 8.9–18.6 min) (p<0.01).
Time to exhaustion during the verification phase was greater
when performing constant load exercise at 85% of peak PO (2.5
±0.4 min) compared to the constant load exercise performed
at 105% of peak PO (1.7 ±0.4 min) (p<0.01). The average
highest ˙
VO2values during the RI test in the whole group were
not significantly different from the ˙
VO2values observed during
the verification phase (Table 1;P=0.33). This response was not
affected by age, with no significant differences identified between
the RI and verification ˙
VO2in O or Y (Table 1;P=0.64).
Similarly, there were no significant differences in the highest ˙
VO2
values during RI test vs. verification phase at either 85% or 105%
of peak PO (P=0.84). The highest ˙
VO2values observed during
both the RI test and the verification phase were highly correlated
(r=0.99; p<0.01) (Figure 1A). The Bland-Altman analysis
revealed a very small absolute bias (−0.25 mL·kg−1·min−1),
which was not different from 0 (z= −1.3), and a precision
of ±1.56 mL·kg−1·min−1between measures (Figure 1B). Bias
±precision was −0.81 ±4.14% when expressed as a percent
of the RI values. Considering an absolute cut-off error of 2
mL·kg−1·min−1, the RI test overestimated ˙
VO2max compared to
the verification phase in 4 participants (or ∼7% of the group) and
underestimated it in 6 participants (or ∼10% of the group).
Peak HR observed during the RI test (171 ±20 b·min−1)
was significantly higher than, and highly correlated with, the
HR response observed during the verification phase (169 ±20
b·min−1;p<0.01; r=0.96; p<0.01). Peak HR during both the
RI test and the verification phase was significantly lower in O (153
±12 b·min−1and 152 ±14 b·min−1, respectively) compared to
Y (188 ±8 b·min−1; and 185 ±9 b·min−1, respectively; p<0.01).
DISCUSSION
This study compared the ˙
VO2responses from a RI test to the
limit of tolerance that was followed by a verification phase to
exhaustion performed at intensities of either 85% or 105% of the
peak PO observed at the end of the RI protocol, in a large and
heterogeneous group of male participants that included older and
younger individuals. The study tested whether the verification
phase (either below or above the end-RI intensity) would produce
a higher ˙
VO2than the maximal value observed during the RI test
and whether such a difference would be affected by verification
phase intensity and/or age. The main findings were that: (1)
the average highest ˙
VO2values observed during the verification
phases were not significantly higher than those obtained during
the RI test; (2) the Bland-Altman analysis revealed a negligible
bias (i.e., not different from zero); (3) the RI ˙
VO2was higher than
the measurement error in ˙
VO2for ∼7% and lower for ∼10% of
the group compared with the verification phase; (4) the difference
between maximal ˙
VO2values associated with the verification
phases compared to the RI tests was unaffected by the age of
participants and verification phase intensity.
In the context of the unresolved uncertainties surrounding the
achievement of a true ˙
VO2max during a RI test to exhaustion,
Poole and Jones (2017) recently proposed that the term ˙
VO2peak
should be avoided and that a verification phase, similar to
that proposed by Rossiter et al. (2006) and further studied by
others (Astorino et al., 2009; Barker et al., 2011; Sedgeman
et al., 2013; Nolan et al., 2014; Sawyer et al., 2015), should
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Murias et al. Verification Does Not Verify ˙
VO2max
TABLE 1 | Highest ˙
VO2and HR values during the ramp incremental (RI) test and the verification phase for each subgroup.
Entire data set Total (n=61) Younger (n=30) Older (n=31)
RI- ˙
VO2(mL·kg−1·min−1) 39.8 ±11.5 48.8 ±7.7 31.2 ±7.1
Verification- ˙
VO2(mL·kg−1·min−1) 40.1 ±11.2 48.8 ±7.5 31.7 ±6.9
RI-HR (b·min−1) 171 ±20* 188 ±8* 153 ±12*
Verification-HR (b·min−1) 169 ±20 185 ±9 152 ±14
Verification 85% Total (n=16) Younger (n=8) Older (n=8)
RI- ˙
VO2(mL·kg−1·min−1) 37.6 ±11.9 47.2 ±6.4 28.0 ±7.1
Verification- ˙
VO2(mL·kg−1·min−1) 37.8 ±11.9 47.6 ±6.1 28.0 ±7.0
RI-HR (b·min−1) 173 ±24* 192 ±6* 151 ±14*
Verification-HR (b·min−1) 170 ±24 189 ±7 148 ±15
Verification 105% Total (n=45) Younger (n=22) Older (n=23)
RI- ˙
VO2(mL·kg−1·min−1) 40.6 ±11.4 49.4 ±8.2 32.3 ±6.9
Verification- ˙
VO2(mL·kg−1·min−1) 40.9 ±10.9 49.2 ±8.1 33.0 ±6.5
RI-HR (b·min−1) 170 ±19* 186 ±8* 154 ±11*
Verification-HR (b·min−1) 169 ±19 184 ±10 153 ±13
Average and standard deviation values of ˙
VO2and HR as derived from the ramp incremental tests (RI) and from the verification trial in the whole group (Total) and in the young and
older subgroups. Data from the entire dataset (that combines all tests irrespective of the validation trial intensity) are presented along with the separate averages of the two intensity
subgroups. *Significantly different from the verification phase (p <0.05).
become a gold standard, especially in older, frail, and/or unfit
populations. The idea that performing a verification phase
at a given power output above that observed during the RI
test to exhaustion is conceptually appealing as this procedure
theoretically confirms that further increases in power output do
not result in greater ˙
VO2values (i.e., an upper limit plateau in
the ˙
VO2response). However, the evidence to support this type
of statement appears surprisingly scant, and this idea neglects
well-established concepts that show that exercising to the limit
of tolerance at any intensity above critical power would result in
attainment of ˙
VO2max.
Data from the present study indicated that, in 61 older and
younger participants, the average highest ˙
VO2values observed
during the RI tests and the verification phase were similar,
irrespective of age, fitness level and verification phase intensity.
These findings confirm, in a larger and more heterogeneous
population, the findings of others (Rossiter et al., 2006; Astorino
et al., 2009; Barker et al., 2011; Sedgeman et al., 2013; Nolan et al.,
2014; Sawyer et al., 2015). In addition, our study provides the
first data of this type in an older adult population. Furthermore,
individual differences between the RI test and the verification
phase displayed quantitatively negligible (likely unmeasurable)
and not significant bias. The results are similar to those in an
athlete sample in whom the ˙
VO2from RI and verification phase
were not different, and within the error of measurement in 24 out
of 24 subjects (Weatherwax et al., 2016).
According to the idea originally proposed by Rossiter et al.
(2006) and examined by others (Astorino et al., 2009; Barker
et al., 2011; Sedgeman et al., 2013; Nolan et al., 2014; Sawyer
et al., 2015), and recently endorsed by Poole and Jones (2017),
the lack of difference in the highest ˙
VO2observed in RI vs.
the verification phase would provide a proof of a plateau in
˙
VO2, in turn confirming the attainment of a true ˙
VO2max.
However, alternate and equally plausible views would be that:
(1) the ˙
VO2max obtained from the RI was “true” in the first
place; (2) both the RI and the validation phase suffer from
similar limitations (i.e., subjects’ inability to endure maximal
effort for a long enough time to allow oxidative metabolism
to display a maximal functional level). In the first view, the
verification phase would not add value beyond performing the
RI test alone for providing a true measure of ˙
VO2max. In the
second view, Poole and Jones (2017) highlighted that in less
experienced participants or those perceived to be less willing to
push themselves to their limit of tolerance, the RI model may
result in a substantial underestimation of ˙
VO2max and in such
cases, a verification phase might offer an opportunity to highlight
such underestimations. The present data set, as well as data from
other studies in sedentary (Astorino et al., 2009), recreationally
active (Sedgeman et al., 2013; Nolan et al., 2014), and overweight
adults (Wood et al., 2010; Sawyer et al., 2015), as well as children
(Barker et al., 2011) does not support the idea that a RI test
underestimates ˙
VO2max compared to a verification phase. These
findings may in fact support a different interpretation: if ˙
VO2max
values derived from a RI test might underestimate the true
˙
VO2max in less experienced/fit/healthy individuals, then these
same people might not be able or willing to endure a maximal
effort during a verification phase. Under these circumstances, the
similar ˙
VO2values observed in both tests might simply represent
that participants are equally fatigued, experiencing tired legs or
feeling somewhat breathless, but they still remain below their
true ˙
VO2max in both conditions. Thus, the verification phase
presenting the same ˙
VO2values as those observed during the RI
test does not imply a plateau that necessarily reflects ˙
VO2max,
or a verification of the RI test, but it might rather reflect
the lack of its attainment in both tests. In this situation, true
achievement of ˙
VO2max is still uncertain but the “illusion” of
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Murias et al. Verification Does Not Verify ˙
VO2max
FIGURE 1 | (A) The highest individual ˙
VO2values observed during the
verification phase (verification- ˙
VO2) are correlated with the values measured
during the ramp incremental test (RI- ˙
VO2). The identity (dashed) and the
correlation (solid) lines are displayed along with the correlation coefficient for
the entire database. Data of subjects who completed the verification phase at
105 and 85% of maximal power output are displayed as filled (•) and empty
circles (◦) respectively. (B) Individual absolute differences (1˙
VO2) between
measures of the highest ˙
VO2during the RI test and the verification phase are
plotted as a function of the average of the two measures. Bias (dashed line)
and precision (limits of agreement, dotted lines), for the entire database, are
displayed along with the numerical values. Data of subjects who completed
the verification phase at 105 and 85% of maximal power output are displayed
as filled (•) and empty circles (◦) respectively.
having measured a true ˙
VO2max is created. Given the difficulties
associated with determination of a true ˙
VO2max value, and the
limitations being highlighted with the verification phase as a
confirmatory test to establish ˙
VO2max, the use of secondary
markers of maximal effort become important. Although it has
been suggested that secondary criteria might not be valid to
provide accurate determination of the attainment of ˙
VO2max
(Midgley et al., 2007; Poole et al., 2008), it could be argued that
commonly used criteria such as [La] above 8 mmol·L−1, a heart
rate response within 10 bpm of the maximal predicted value, an
RER higher than 1.10, and an RPE >18, might contribute to feel
confidence in the attainment of a true ˙
VO2max at the end of a RI
test.
Perhaps the recommendation for the utilization of a
verification phase should recognize that the aim of this approach
is not to identify ˙
VO2max in a majority of participants, but to find
the minority of participants who might not achieve it during a
RI test. Nevertheless, with a precision of ∼1.5 mL·kg−1·min−1
within the minimum detectable change of 2 mL·kg−1·min−1,
indeed the verification phase revealed very few instances of an
underestimation from the RI. Interestingly, the data from the
present study showed that the ˙
VO2values during the RI test
similarly over- (i.e., four tests) and underestimated (i.e., six tests)
the ˙
VO2values associated with the verification phase, suggesting
major limitations in this verification procedure.
In relation to the effectiveness of the verification phase
to reach ˙
VO2max, the relationship between the intensity and
the duration of the exercise should be considered. In the
present study, the times to exhaustion for the verification phases
performed five min after the end of the RI test were ∼2.5 and
∼1.5 min for exercise performed at 85% and 105% of the peak
PO, respectively. Although this time might be considered too
short for ˙
VO2max to develop (especially for more intense and
shorter exercise bouts) (Poole and Jones, 2012), the fact that the
verification phases were performed shortly after the end of the
RI test and that the system was “primed” (De Roia et al., 2012)
might have contributed to the achievement of a ˙
VO2response
that was as high as that seen toward the end of the RI test. While
some papers have used supramaximal intensities of exercise for
the verification phases in order to establish a “plateau response”
despite an increase in PO beyond that observed during the RI
test (Astorino et al., 2009; Barker et al., 2011; Nolan et al., 2014),
Sedgeman et al. (2013) compared a verification phase performed
at 105% of the peak PO during the RI test to a verification phase
performed at a PO equivalent to that occurring two stages before
the end of a graded test (i.e., ∼54 W lower PO or ∼82% of peak
PO), subsequent to 3 min recovery after the end of the RI test. As
found for the present data using 85% or 105% of the end-RI work
rate, Sedgeman et al. (2013) also showed the ˙
VO2values were
not different between the RI test and the verification phase either
with the sub-maximal (∼2.2 min duration) or the supramaximal
(∼1.3 min duration) verification. These authors suggested that
a sub-maximal verification phase might be beneficial as more
plateau responses were observed during this type of verification.
This interpretation is not surprising; exercising within the very
heavy intensity domain (such as in Sedgeman et al. and the
present studies) is compatible with a longer exercise duration,
in turn allowing enough time for the slow component of ˙
VO2
to develop and for ˙
VO2max to be achieved. On the contrary,
exercising in the severe intensity domain (e.g., 105% of peak
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Murias et al. Verification Does Not Verify ˙
VO2max
PO) might pose some extra challenges for confirmation of a true
˙
VO2max as a plateau response is less likely to occur and, although
not the case in the present study and in that of Sedgeman
et al., could theoretically result in muscle fatigue before the ˙
VO2
response can be fully developed and ˙
VO2max expressed (Poole
and Jones, 2012). This is an important aspect to consider as the
duration of recovery period before the verification phase and/or
the characteristics of the ramp during the incremental test to
exhaustion (i.e., steeper ramps will result in higher peak POs
compared to less steep ramps) might determine whether or not
the highest possible ˙
VO2is achieved when the intensity of the
verification phase is supramaximal.
In the present study, the verification phase at 85% and 105% of
peak PO were collected in two different laboratories, which might
represent a possible limitation. However, the equipment used in
both laboratories was comparably accurate and precise and the
experimental procedures were consistent between laboratories
and clearly described to allow replication. Furthermore, since
the analysis compares ˙
VO2values obtained with the RI test and
verification phase within each individual, whatever systematic
bias in ˙
VO2measures might exist between laboratories would
affect both data-points in the same way. As for the vast majority
of the studies that have described the use of a verification
phase, the population tested in the present study is limited
to male participants. It was important to verify the usefulness
of the verification phase in the same population in which the
verification phase has been proposed; however, the absence
of female participants in this study is an issue that, although
not expected to change the outcome observed in the present
investigation, might need to be addressed in future studies.
In conclusion, the accurate identification of ˙
VO2max remains
an elusive issue and there is a clear need for developing reliable
criteria to objectively evaluate the achievement of a true maximal
response. In this context, the proposal by Poole and Jones (2017)
to use the verification phase for true ˙
VO2max determination
appeared a very promising approach to overcome the absence
of an objective plateau in ˙
VO2. However, data presented in this
study indicate that a verification phase performed subsequent to
the end of a RI test does not provide a convincing confirmation
that a true ˙
VO2max response has been achieved. Therefore, the
recommendation that a verification phase should become the
gold standard procedure for ˙
VO2max determination, although
initially appealing, is not supported. As such, the verification
phase should not be accepted as a gold standard, and given the
present analysis indicating that in most cases the ˙
VO2during
the RI test is as high as that of the verification phase, or that the
highest ˙
VO2in the few cases observed on either the RI test or the
verification phase is within the error of the measurement, further
efforts to endorse the verification phase to confirm ˙
VO2max do
not seem to be a tenable direction for future research.
AUTHOR CONTRIBUTIONS
JM, SP, and DP: contributed to the conception of the work,
analysis, and interpretation of data; JM, SP, and DP: contributed
to the drafting and revisions of the manuscript; JM, SP, and
DP: approved the final version of this manuscript; JM, SP,
and DP: agree to be accountable for all aspects of the work
in ensuring that questions related to the accuracy or integrity
of any part of the work are appropriately investigated and
resolved.
FUNDING
The work performed at The University of Western Ontario was
supported by Natural Sciences and Engineering Research Council
of Canada.
ACKNOWLEDGMENTS
We would like to express our gratitude to the participants in this
study.
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Conflict of Interest Statement: The authors declare that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
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