Physiological Reports. 2021;9:e15037. 
 
  | 1 of 14
https://doi.org/10.14814/phy2.15037
wileyonlinelibrary.com/journal/phy2
Received: 19 May 2021 | Revised: 20 August 2021 | Accepted: 26 August 2021
DOI: 10.14814/phy2.15037  
O R I G I N A L  A R T I C L E
Comparison of constant load exercise intensity for 
verification of maximal oxygen uptake following a graded 
exercise test in older adults
Ian R. Villanueva1 |   John C. Campbell1 |   Serena M. Medina1 |   Theresa 
M. Jorgensen1 |   Shannon L. Wilson1 |   Siddhartha S. Angadi2 |   Glenn A. Gaesser1 |   
Jared M. Dickinson3
This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided 
the original work is properly cited.
© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society
1Arizona State University, Phoenix, 
Arizona, USA
2Department of Kinesiology, University 
of Virginia, Charlottesville, Virginia, 
USA
3Department of Health Sciences, 
Central Washington University, 
Ellensburg, Washington, USA
Correspondence
Jared M. Dickinson, Department of 
Health Sciences, Central Washington 
University, 400 E University Way, 
Ellensburg, WA 98926, USA.
Email: jared.dickinson@cwu.edu
Funding information
No funding information provided.
Abstract
Maximal oxygen uptake (VO2max) declines with advancing age and is a predic-
tor of morbidity and mortality risk. The purpose here was to assess the utility 
of constant load tests performed either above or below peak work rate obtained 
from a graded exercise test for verification of VO2max in older adults. Twenty- 
two healthy older adults (9M, 13F, 67 ± 6 years, BMI: 26.3 ± 5.1 kg·m−2) par-
ticipated in the study. Participants were asked to complete two experimental 
trials in a randomized, counterbalanced cross- over design. Both trials (cycle er-
gometer) consisted of (1) an identical graded exercise test (ramp) and (2) a con-
stant load test at either 85% (CL85; n = 22) or 110% (CL110; n = 20) of the peak 
work rate achieved during the associated ramp (performed 10- min post ramp). 
No significant differences were observed for peak VO2 (L·min−1) between CL85 
(1.86 ± 0.72; p = 0.679) or CL110 (1.79 ± 0.73; p = 0.200) and the associated ramp 
(Ramp85, 1.85 ± 0.73; Ramp110, 1.85 ± 0.57). Using the study participant's mean 
coefficient of variation in peak VO2 between the two identical ramp tests (2.9%) 
to compare individual differences between constant load tests and the associated 
ramp revealed 19/22 (86%) of participants achieved a peak VO2 during CL85 that 
was similar or higher versus the ramp, while only 13/20 (65%) of participants 
achieved a peak VO2 during CL110 that was similar or higher versus the ramp. 
These data indicate that if a verification of VO2max is warranted when testing 
older adults, a constant load effort at 85% of ramp peak power may be more likely 
to verify VO2max as compared to an effort at 110% of ramp peak power.
K E Y W O R D S
aerobic power, aging, exercise physiology, verification, VO2max, VO2peak
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VILLANUEVA et al.
1 | INTRODUCTION
Advancing age is associated with a variety of physiologi-
cal and biological changes that can contribute to impaired 
physical function. Of particular interest is the steady de-
cline in the maximal rate of oxygen uptake (VO2max) that 
is well documented during advancing age (Betik & Hepple, 
2008; Gries et al., 1985; Kaminsky et al., 2015). Not only is 
a reduced VO2max in older adults associated with func-
tional limitations, such as difficulty with walking, climb-
ing stairs, and performing daily activities (Kaminsky et al., 
2013; Paterson et al., 1999, 2004; Paterson & Warburton, 
2010), but a low VO2max is a powerful independent pre-
dictor of cardiovascular disease and all- cause mortality 
(Imboden et al., 2018; Kokkinos et al., 2010; Myers et al., 
2002; Ross et al., 2016). Moreover, the addition of VO2max 
to other traditional risk factors improves risk stratifica-
tion, and inclusion of VO2max to classify morbidity and 
mortality risk may be particularly powerful for those on 
the lower end of the VO2max spectrum, such as older 
adults (Ross et al., 2016). Consequently, developing effec-
tive exercise testing strategies that can be used to verify a 
maximal exercise effort, and thus VO2max, in older adults 
could have important implications for accurate assess-
ment of morbidity and mortality risk in this population.
Traditionally, VO2max is often assessed through the use 
of a graded exercise test, employing either a steady ramp 
or an incremental step test until volitional exhaustion. In 
theory, a VO2max is achieved when there is no increase 
in VO2 with a concomitant increase in power or speed 
(Day et al., 2003; Hill & Lupton, 1923; Taylor et al., 1955), 
which is often referred to as a VO2 plateau (Taylor et al., 
1955). While sampling rate/interval can influence the oc-
currence of a plateau in VO2 (Astorino, 2009), a plateau is 
not always observed, and in fact has been found to only 
occur in 17% of VO2max assessments (Day et al., 2003). 
The absence of an observed VO2 plateau has produced 
queries as to the validatity of these tests for accurately 
assessing VO2max (Day et al., 2003; Howley et al., 1995; 
Midgley & Carroll, 2009; Poole et al., 2008). Consequently, 
the development of secondary criteria that are predicated 
on expected values for respiratory exchange ratio, heart 
rate (HR), and blood lactate, for example, have been used 
to validate a maximal effort (Howley et al., 1995; Midgley 
et al., 2007, 2009; Wagner et al., 2020). However, the use 
of these secondary criteria is problematic (Poole & Jones, 
2017) as these criteria can often be achieved at a “submax-
imal” effort (Poole et al., 2008).
More recently, the use of a secondary constant load test 
that is performed following a graded exercise test has been 
implemented as a strategy to verify a maximal effort and 
VO2max (Costa et al., 2021; Midgley & Carroll, 2009; Poole 
et al., 2008). While the use of a constant load test to verify 
VO2max has gained consideration, the intensity at which 
these constant load tests have been performed is vari-
able. For instance, these constant load bouts have been 
performed at work rates below (Day et al., 2003; Murias 
et al., 2018; Rossiter et al., 2006; Sedgeman et al., 2013), 
equal to (Sawyer et al., 2015), or above (Astorino et al., 
2009; Barker et al., 2011; Hawkins et al., 2007; Iannetta 
et al., 2020; Kuffel et al., 2005; Leicht et al., 2013; Midgley 
et al., 2006; Murias et al., 2018; Nolan et al., 2014; Poole 
et al., 2008; Rossiter et al., 2006; Scharhag- Rosenberger 
et al., 2011; Sedgeman et al., 2013; Weatherwax et al., 
2016) those achieved during the preceding graded exer-
cise test [most previous studies employ constant load tests 
between 85% and 115% of peak work rate (Astorino et al., 
2009; Barker et al., 2011; Dalleck et al., 2012; Hawkins 
et al., 2007; Iannetta et al., 2020; Kuffel et al., 2005; Leicht 
et al., 2013; Midgley & Carroll, 2009; Midgley et al., 2006; 
Murias et al., 2018; Niemela et al., 1980; Nolan et al., 2014; 
Poole et al., 2008; Rossiter et al., 2006; Sawyer et al., 2015; 
Scharhag- Rosenberger et al., 2011; Sedgeman et al., 2013; 
Weatherwax et al., 2016)]. Furthermore, there is lack of 
agreement on the work rate at which the constant load 
tests should be performed to best verify a maximal effort 
(Breda et al., 1985; Iannetta et al., 2020; Poole & Jones, 
2017). Specifically, some propose that if a VO2max is to be 
verified, the constant load effort needs to be conducted at 
a work rate higher than that achieved during the graded 
exercise test (Poole & Jones, 2017). On the other hand, 
recent evidence indicates that a work rate below that 
achieved during the graded exercise test is more likely to 
verify a maximal effort (Iannetta et al., 2020). In partic-
ular, the use of a “submaximal” constant load work rate 
to verify VO2max may be more reliable versus the “supra-
maximal” work rate when coupled with graded exercise 
test protocols that are shorter in duration (e.g., steeper 
ramp protocols) (Iannetta et al., 2020). Consequently, the 
use of a constant load work rate below the peak work rate 
achieved during the graded exercise test may be a more 
reliable strategy to verify VO2max in individuals with a 
lower VO2max, such as older adults, who may experience 
shorter graded exercise tests.
Therefore, the primary purpose of this study was to em-
ploy a cross- over design to assess the utility of a constant 
load test performed at a work rate below (85%) and a work 
rate above (110%) the peak work rate achieved during a 
graded exercise test (ramp) for validating a maximal ef-
fort and verifying VO2max in healthy older adults. While 
comparison of constant load intensities above and below 
the peak achieved during a ramp test has been previously 
reported (Murias et al., 2018), to our knowledge no study 
has employed a randomized, counterbalanced cross- over 
design. We hypothesized that in healthy older adults, the 
constant load test below the peak work rate of the ramp 
   | 3 of 14
VILLANUEVA et al.
test would be more likely to verify a maximal effort and 
VO2max, which would be demonstrated by a greater num-
ber of individuals achieving a peak VO2 value during the 
constant load effort below peak work rate that is similar or 
higher to the ramp test as compared to the constant load 
effort above peak work rate. In addition, the randomized 
cross- over design of the study included the performance 
of two identical ramp tests by each participant. Therefore, 
a secondary purpose of this study was to evaluate a second 
identical ramp test as a strategy to verify VO2max in older 
adults.
2 | MATERIALS AND METHODS
2.1 | Participants
Twenty- four healthy older adults volunteered to partici-
pate in this study. All participants were between the ages 
of 60– 80 years and were recruited by advertisement, locally 
posted flyers, and word of mouth. Participants completed a 
brief online pre- screening questionnaire to assess general 
health characteristics which was reviewed by a member 
of the research team. Following the pre- screening ques-
tionnaire, qualified participants were invited to the labo-
ratory for a formal informed consent process. Additional 
screening included a medical history, the Physical Activity 
Readiness Questionnaire for Everyone (PARQ+), and 
assessment of resting blood pressure. Participants were 
excluded if they had uncontrolled hypertension, or any 
self- reported heart, liver, kidney, blood, or respiratory dis-
ease, peripheral vascular disease, diabetes or endocrine 
disease, active cancer or use of tobacco, self- reported acute 
or chronic illness, medical/orthopedic conditions preclud-
ing exercise, or if they were currently training for an en-
durance event (i.e., marathon, triathlon). All participants 
provided written informed consent prior to participation. 
Participant characteristics for those that participated in the 
study are presented in Table 1. This study was approved by 
the University Institutional Review Board (in compliance 
with the Declaration of Helsinki, as revised in 1983).
2.2 | Study design and procedures
Participants were studied during two separate experimen-
tal trials. The experimental trials were separated on av-
erage by 9 days (range, 6– 14 days) and were performed 
in a randomized, counterbalanced cross- over design at a 
similar time of day (e.g., morning vs. afternoon). Each ex-
perimental trial consisted of a graded exercise ramp test 
and a constant load test that was performed after 10 min 
of active rest (pedaling at a work rate no higher than the 
warm- up) following completion the ramp test. The ramp 
tests were identical for each experimental trial, however, 
the visits differed in the work rate at which the subsequent 
constant load test was performed.
During each experimental trial participants reported to 
the laboratory for testing at least 3 h postprandial and after 
abstaining from caffeine, alcohol, supplements, and exer-
cise for at least 24 h. The participant's height and weight 
were measured on a calibrated stadiometer and resting 
blood pressure measures were obtained during each visit 
(Dinamap® PRO 100 Vital Signs Monitor; GE Healthcare). 
Participants were equipped with a mouthpiece connected 
to a standard nonrebreathing valve (Hans Rudolph) for 
continuous measurement of ventilation and respiratory 
gas exchange data using a TrueOne 2400 metabolic cart 
(Parvomedics). A standard calibration was performed 
before each test per manufacturer recommendations. 
Participants were also equipped with a chest worn HR mon-
itor (Polar, Inc.) to continuously monitor HR. After 2 min 
of rest, participants performed a standardized warm- up in 
which the participants pedaled at a cadence of their choice, 
between 50 and 90 revolutions per minute (RPM), on a sta-
tionary cycle ergometer (Ergoline Viasprint 150) at 50 W 
for males and 40 W for females for 5 min. The chosen RPM 
was maintained for the remainder of the testing.
Ramp test
During both experimental trials, participants performed 
an identical ramp test on a cycle ergometer. Immediately 
following the warm- up phase (described above), the work 
rate on the cycle ergometer was increased in a ramp fash-
ion corresponding to 20 W·min−1 for males (1 W every 3 s) 
and 15 W·min−1 for females (1 W every 4 s) until volitional 
exhaustion. Ratings of perceived exertion (RPE) were as-
sessed every 60 s throughout the duration of the ramp test. 
The test was terminated at volitional exhaustion or if the 
TABLE 1 Participant characteristics
Men 
(n = 9)
Women 
(n = 13)
Total 
(n = 22)
Age, year
69 ± 6
65 ± 6
67 ± 6
Height, cm
172 ± 9
161 ± 5
165 ± 9
Weight, kg
77 ± 18
69 ± 16
72 ± 17
BMI, kg·m−2
26.0 ± 4.1
26.6 ± 5.8
26.3 ± 5.1
Body fat, %
28.1 ± 6.0
37.8 ± 10.5
34.0 ± 10.0
Lean body mass, kg
53 ± 12
39 ± 3
44 ± 10
Data are presented as mean ± SD.
Abbreviation: BMI, body mass index; Body fat % is whole body derived from 
dual energy x- ray absorptiometry.
4 of 14 |   
VILLANUEVA et al.
participant was unable to maintain his/her RPM despite 
verbal encouragement.
Constant load test
During each experimental trial a constant load test was 
completed following the ramp test, which occurred after 
10 min of light active recovery (pedaling at a work rate 
no higher than the warm- up) on the stationary ergometer. 
During active recovery, the participants were provided a 
break from the breathing valve, which was reconnected to 
the participant at least 3 min prior to the start of the con-
stant load test. The constant load test consisted of cycling 
at a work rate equivalent to either 85% (CL85) or 110% 
(CL110) of the peak work rate reached during the preced-
ing ramp test. Specifically, in a randomized, counterbal-
anced cross- over design, participants were randomized 
to perform either CL85 or CL110 during the first visit, 
whereas during the second visit the participant completed 
the constant load test at the other work rate. Participants 
were instructed to increase cadence as the resistance on 
the cycle ergometer increased from that during active re-
covery to the prescribed intensity. Both constant load tests 
were performed at a constant work rate until volitional 
exhaustion. RPE was assessed at the end of the constant 
load test. The test was terminated at volitional exhaustion 
(i.e., the participant requesting to stop) or if the partici-
pant was unable to maintain his/her RPM despite verbal 
encouragement.
Assessment of body composition
During the second visit, participants underwent a dual- 
energy x- ray absorptiometry (DEXA) whole- body scan 
(Lunar iDXA, GE Healthcare). The DEXA was per-
formed prior to any testing and after voiding the bladder. 
Participants laid down on the DEXA for 15 min prior to 
the DEXA to avoid any influence of fluid shifts. A trained 
and certified radiologist administered the DEXA scan.
2.3 | Assessment of physiological  
outcomes
All ventilation and gas exchange data were assessed using 
10- s average measurements, with O2 and CO2 concentra-
tion of expired air derived from samples obtained from a 
mixing chamber. Peak VO2 values for the ramp tests and 
constant load tests were taken as the highest three con-
secutive 10- s measurements, which were averaged to yield 
data collected over a 30- s timeframe. Peak RER values 
were taken as an average of the three 10- s measurements 
at the same time point as peak VO2. Peak HR for the ramp 
and constant load tests were taken as the highest recorded 
HR. Peak power during the ramp was identified as the 
highest work rate achieved prior to a drop in cadence or 
volitional exhaustion. Individual data were calculated to 
determine the percent change of physiological outcomes 
between the constant load test and the associated ramp, 
as well as between the ramp during the first visit (Ramp1) 
compared to the ramp during the second visit (Ramp2). 
The mean coefficient of variation (CV) for Ramp1 and 
Ramp2 was used to identify if a similar (within CV) or 
a higher or lower value (outside CV) for a physiological 
variable occurred between the constant load test and the 
associated ramp test and between Ramp1 and Ramp2.
2.4 | Statistical analysis
All data were tested for normality through skewness and 
kurtosis analyses and visual inspection of the normality 
plots using SPSS v.24 (IBM). A one- way, repeated meas-
ures, analysis of variance (ANOVA) was used to assess 
differences between the ramp tests and the constant load 
tests for all outcomes. Pairwise comparisons were per-
formed following the ANOVA using a least significant 
difference (LSD) post hoc analyses adjusted for the fol-
lowing two comparisons: constant load test at 85% of peak 
work rate (CL85) versus the associated ramp (Ramp85); 
and constant load test at 110% of peak work rate (CL110) 
versus the associated ramp (Ramp110). Outcome vari-
ables obtained from the first (Ramp1) and second ramp 
test (Ramp2) were compared using a dependent t- test 
for equivalence. Pearson's correlations were used to de-
termine the relationships between variables for the con-
stant load test versus ramp and for Ramp1 versus Ramp2. 
Bland– Altman plots and CVs were used to compare the 
agreement for all variables between the constant load 
test and associated ramp test and between Ramp1 and 
Ramp2. Intraclass correlation coefficients (ICCs) were 
used to examine the reliability of peak VO2 and peak HR 
between the constant load test and associated ramp test 
and between Ramp1 and Ramp2. All comparisons includ-
ing a constant load test were made to the ramp performed 
during the same experimental trial. Pearson's correlations 
were also used to examine the following relationships 
within each experimental trial: (1) Difference in peak 
VO2 (L·min−1) between CL85 and Ramp85 and time to ex-
haustion for CL85, (2) Difference in peak VO2 (L·min−1) 
between CL85 and Ramp85 and time to exhaustion of 
Ramp85, (3) Difference in peak VO2 (L·min−1) between 
CL110 and Ramp110 and time to exhaustion of CL110, 
and (4) Difference in peak VO2 (L·min−1) between CL110 
   | 5 of 14
VILLANUEVA et al.
and Ramp110 and time to exhaustion during Ramp110. 
All data were analyzed using SPSS Software (SPSS v24) 
and significance was set a priori at p ≤ 0.05. All data are 
presented as means ± SD.
3 | RESULTS
Of the 24 participants who enrolled in the study, two 
participants were excluded during the screening process 
(one for high blood pressure, one for underlying medical 
disease). Two additional participants dropped out of the 
study after completing the first visit due to circumstances 
unrelated to the study. Both of these participants only 
completed the CL85 exercise trial, and these participants 
were included in the analysis for ramp versus CL85 (e.g., 
CL85, n = 22; CL110, n = 20). Only participants who com-
pleted both trials (n = 20; 67 ± 6 year, 8 males and 12 fe-
males) were included in the comparisons between Ramp1 
and Ramp2. Participant characteristics are presented in 
Table 1. In addition, the peak VO2 (mLO2·kg−1·min−1) 
and peak HR of these participants are expressed relative 
to age- based reference standards (Kaminsky et al., 2015) 
in Table 2.
3.1 | Ramp versus constant load test 
(group data)
Peak VO2 (L·min−1) did not differ (p  =  0.679) be-
tween Ramp85 (1.85  ±  0.73  L·min−1) and CL85 
(1.86  ±  0.72  L·min−1) (CV  =  2.07  ±  2.14%) (Table 3, 
Figures 1a and 2a). Similarly, peak VO2 was not sig-
nificantly different (p  =  0.200) between Ramp110 
(1.85 ± 0.57 L·min−1) and CL110 (1.79 ± 0.73 L·min−1) 
(CV  =3.64%  ±  4.47%) (Table 3, Figures 1b and 2b). 
Intraclass correlations also showed agreement in peak 
VO2 (L·min−1) between the ramp and constant load test 
for both CL85 (ICC = 0.997) and CL110 (ICC = 0.979) 
(Table 3). Time to exhaustion during the ramp and con-
stant load tests were examined to determine whether 
time to exhaustion of the various tests influenced differ-
ences in peak VO2 between the constant load test and 
associated ramp. Time to exhaustion for Ramp85 was not 
statistically correlated with the difference in peak VO2 
between CL85 and Ramp85 (r = 0.17; p = 0.458) (Figure 
3a). However, a longer Ramp110 time to exhaustion was 
negatively associated with the difference in peak VO2 be-
tween CL110 and Ramp110 (r = 0.48; p = 0.031) (Figure 
3b), indicating that a longer time to exhaustion during 
the ramp test was associated with a greater likelihood of 
attaining a lower peak VO2 during CL110 compared to 
the ramp. Time to exhaustion for the respective constant 
load test protocols was not statistically correlated with 
the difference in peak VO2 between CL85 and the associ-
ated ramp (r = 0.33; p = 0.134) (Figure 3c) or between 
CL110 and the associated ramp (r  =  0.20; p  =  0.393) 
(Figure 3d).
Peak HR did not differ (p = 0.243) between Ramp85 
(150  ±  17  bpm) and CL85 (153  ±  17  bpm) (Table 3, 
Figures 1c and 2c). Similarly, peak HR did not differ 
(p = 0.085) between Ramp110 (149 ± 16 bpm) and CL110 
(146 ± 16 bpm) (Table 3, Figures 1d and 2d). Intraclass 
correlations showed agreement in peak HR between 
ramp and constant load test for both CL85 (ICC = 0.950) 
and CL110 (ICC  =  0.906). Peak RER was significantly 
different (p < 0.01) between Ramp85 (1.17 ± 0.09) and 
CL85 (1.07 ± 0.08) (Table 3). Similarly, peak RER was 
significantly different (p  <  0.01) between Ramp110 
(1.16 ± 0.08) and CL110 (1.03 ± 1.0) (Table 3). Peak RPE 
did not differ (p = 0.602) between Ramp85 (18.5 ± 1.3) 
and CL85 (18.3 ± 1.7). Similarly, peak RPE did not differ 
(p = 0.629) between Ramp110 (18.7 ± 1.0) and CL110 
(18.6 ± 1.1).
Study participants
Reference
Percentile
Males
Peak VO2 
(mlO2·kg−1·min−1)
29.8 ± 9.6 (18.5– 49.9)
29.4 ± 7.9
~50th
Peak HR (bpm)
159 ± 17 (135– 186)
158 ± 17
N/A
Females
Peak VO2 
(mLO2·kg−1·min−1)
24.2 ± 10.5 (14.1– 47.9)
20.7 ± 5.0
~75th
Peak HR (bpm)
147 ± 17 (120– 175)
157 ± 17
N/A
Study Participant data (9M, 13F, 67 ± 6 years) are presented as mean ± SD (range) from the first visit 
ramp test. Reference and percentile data are derived from FRIEND for age 60– 69 years (Kaminsky et al., 
2015).
Abbreviation: bpm, beats per minute.
TABLE 2 Study participants relative 
peak VO2 (mLO2·kg−1·min−1) and heart 
rate (HR) in comparison to reference 
standards derived from FRIEND 
(Kaminsky et al., 2015)
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VILLANUEVA et al.
3.2 | Ramp1 versus Ramp2 (group data)
Peak VO2 during Ramp1 (1.82  ±  0.72  L·min−1) was 
not significantly different (p  =  0.100) from Ramp2 
(1.86 ± 0.81 L·min−1) (CV = 2.90 ± 1.89%) (Table 3). Peak 
VO2 was also strongly correlated (R2 = 0.987) (p < 0.01) and 
was in high agreement (ICC = 0.994) between Ramp1 and 
Ramp2 (Figure 4). Peak HR did not differ (p = 0.115) be-
tween Ramp1 (150 ± 17 bpm) and Ramp2 (149 ± 15 bpm) 
(CV = 2.30 ± 2.06%) (Table 3) and values were strongly 
correlated (R2 = 0.876) (p < 0.01) and in high agreement 
(ICC = 0.936) between Ramp1 and Ramp2. RER did not 
differ (p = 0.348) between Ramp1 (1.16 ± 0.09) and Ramp2 
(1.16 ± 0.08) (CV = 3.20 ± 2.05%) (Table 3) and values 
were correlated (R2 = 0.529) (p < 0.01) (Table 3) and in 
agreement (ICC = 0.727). Peak power output (W) did not 
differ between Ramp1 (156 ± 53) and Ramp2 (158 ± 53) 
(CV = 5.3 ± 5.40%) (Table 3) and values were strongly 
correlated (R2 = 0.905) (p < 0.01) and in high agreement 
(ICC = 0.951) between Ramp1 and Ramp2. RPE did not 
differ (p = 0.481) between Ramp1 (18.5 ± 1.1) and Ramp2 
(18.6  ±  1.3) and values were correlated (R2  =  0.480) 
(p < 0.01).
3.3 | Individual data
We calculated the mean individual participant CV (%) 
between Ramp1 and Ramp2 to examine individual dif-
ferences in physiological variables between the ramps 
(Ramp1 vs. Ramp2) and between the constant load tests 
and their associated ramp tests. Using this participant- 
based CV- derived cut point from Ramp1 and Ramp2 (see 
Table 3), 68% of participants (15 of 22) achieved a peak 
VO2 during CL85 that was similar (within 2.9%, CV be-
tween Ramp1 and Ramp2 for peak VO2) to the associated 
TABLE 3 Physiological group and individual responses to the ramp and constant load tests
Peak VO2 
(L·min−1)
Peak HR 
(bpm)
VE 
(L·min−1)
Peak RER
Power 
(W)
Time to 
exhaustion (s)
CV (%)a 
2.9
2.3
6.3
3.2
5.3
8.0
Ramp 1 versus Ramp 2
Ramp1
1.82 ± 0.72
150 ± 17
76.91 ± 31.69
1.16 ± 0.09
156 ± 53
402 ± 151
Ramp2
1.86 ± 0.81
149 ± 15
79.31 ± 31.84
1.16 ± 0.08
158 ± 53
408 ± 160
Ind. Similarb 
(9/20)
(9/19)
(9/20)
(7/20)
(9/20)
(9/20)
Ind. Higherb 
(8/20)
(3/19)
(6/20)
(5/20)
(7/20)
(6/20)
Ind. Lowerb 
(3/20)
(7/19)
(5/20)
(8/20)
(4/20)
(5/20)
Ramp versus constant load test at 85%
Ramp
1.85 ± 0.73
150 ± 17
77.85 ± 30.01
1.17 ± 0.09
158 ± 52
401 ± 142
CL85
1.86 ± 0.72
153 ± 17
80.15 ± 30.20
1.07 ± 0.08*
133 ± 45
185 ± 88
Ind. Similarb 
(15/22)
(11/21)
(10/22)
(1/22)
Ind. Higherb 
(4/22)
(7/21)
(8/22)
(2/22)
Ind. Lowerb 
(3/22)
(3/21)
(4/22)
(19/22)
Ramp versus constant load test at 110%
Ramp
1.85 ± 0.57
149 ± 16
78.28 ± 33.63
1.16 ± 0.08
156 ± 54
410 ± 162
CL110
1.79 ± 0.73
146 ± 16
75.83 ± 34.83
1.03 ± 0.10*
170 ± 60
79 ± 62
Ind. Similarb 
(8/20)
(7/19)
(9/20)
(2/20)
Ind. Higherb 
(5/20)
(3/19)
(6/20)
(0/20)
Ind. Lowerb 
(7/20)
(9/19)
(5/20)
(18/20)
Data are presented as mean ± SD.
aMean individual participant coefficient of variation (CV) from Ramp1 to Ramp2, presented as percent (%).
bNumber of participants with values within the CV (for Ramp1 to Ramp2) between tests (similar), a value that is identified as higher (>CV for Ramp1 to 
Ramp2) compared to the Ramp (or compared to Ramp 1 for Ramp2 vs. Ramp1) (higher), a value that is identified as lower (>CV for Ramp1 to Ramp2) 
compared to the Ramp (or compared to Ramp 1 for Ramp2 vs. Ramp1) (lower). HR, heart rate; RER, respiratory exchange ratio; VE, ventilation; Ind. Similar, 
represents the number of participants that achieved a similar value (within CV) during the constant load test versus the associated ramp or for Ramp2 versus 
Ramp1; Ind. Higher, represents the number of participants that achieved a higher value (outside CV) during the constant load (CL) test versus the associated 
ramp or for Ramp2 versus Ramp1; Ind. Lower, represents the number of participants that achieved a lower value (outside CV) during the constant load test 
versus the associated ramp or for Ramp2 versus Ramp1.
*p < 0.05 Ramp.
   | 7 of 14
VILLANUEVA et al.
FIGURE 1 Bland– Altman plots for peak oxygen uptake (VO2, L·min−1) and heart rate (HR). Presented are (a) peak VO2 obtained 
during the constant load test performed at 85% of ramp peak work rate (CL85) and the associated ramp test (Ramp85), (b) peak VO2 
obtained during the constant load test performed at 110% of ramp peak work rate (CL110) and the associated ramp test (Ramp110), (c) 
peak HR obtained during CL85 and Ramp85, and (d) peak HR obtained during CL110 and Ramp110. Y- axis = constant load test − ramp; 
x- axis = mean of ramp and constant load test; dotted lines = mean ± 1.96 × SD; dark solid lines = 0 on the y- axis; light solid lines = mean 
of constant load test − ramp. Filled squares (■) represent male participants and open diamonds (♢) represent female participants. Ramp85 
versus CL85, n = 22; Ramp110 versus CL110, n = 20
(a)
(c)
(d)
(b)
FIGURE 2 Peak oxygen uptake (VO2, L·min−1) and heart rate (HR) achieved during the ramp (x- axis) and constant load (y- axis) test 
for each participant. The dotted lines represent the line of identity (y = x). Presented are (a) peak VO2 obtained during the constant load 
test at 85% of ramp peak work rate (CL85) versus the associated ramp (Ramp85), (b) peak VO2 obtained during the constant load test at 
110% of ramp peak work rate (CL110) versus the associated ramp (Ramp110), (c) peak HR obtained during CL85 versus Ramp85, and (d) 
peak HR obtained during CL110 versus Ramp110. Filled squares (■) represent male participants and open diamonds (♢) represent female 
participants. Ramp85 versus CL85, n = 22; Ramp110 versus CL110, n = 20
(a)
(c)
(d)
(b)
8 of 14 |   
VILLANUEVA et al.
ramp peak VO2. Furthermore, 18% of participants (4 of 22) 
achieved a peak VO2 during CL85 that was >2.9% higher 
than that achieved during Ramp85, while 14% of partici-
pants (3 of 22) achieved a peak VO2 during CL85 that was 
>2.9% lower than that achieved during Ramp85 (Table 3). 
In contrast, 40% of participants (8 of 20) achieved a peak 
VO2 during CL110 that was similar to the associated ramp, 
25% of participants (5 of 20) achieved a peak VO2 during 
CL110 that was >2.9% higher than Ramp110 (Table 3), 
and 35% of participants (7 of 20) achieved a peak VO2 dur-
ing CL110 that was >2.9% lower than Ramp110. Similar 
results were observed between CL85 and CL110 for peak 
HR and ventilation (Table 3).
When comparing Ramp2 to Ramp1, 45% of participants 
(9 of 20) achieved a peak VO2 during Ramp2 that was 
similar to Ramp1, 40% of participants (8 of 20) achieved 
FIGURE 3 Correlations between time to exhaustion (x- axis) and differences in peak oxygen uptake (VO2, L·min−1) achieved during the 
constant load and ramp tests. Presented are (a) time to exhaustion during the associated ramp (Ramp85) compared to the difference in peak 
VO2 obtained during the constant load test at 85% of ramp peak power (CL85) and Ramp85, (b) time to exhaustion during the associated 
ramp (Ramp110) compared to the difference in peak VO2 obtained during the constant load test at 110% of ramp peak power (CL110) and 
Ramp110, (c) time to exhaustion during CL85 compared to the difference in peak VO2 obtained during CL85 and Ramp85, and (d) time to 
exhaustion during CL110 compared to difference in peak VO2 obtained during CL110 and Ramp110. *p < 0.05. Filled squares (■) represent 
male participants and open diamonds (♢) represent female participants. Ramp85 versus CL85, n = 22; Ramp110 versus CL110, n = 20
(a)
(b)
(c)
(d)
FIGURE 4 Comparison of peak VO2 values (L·min−1) achieved during the first ramp test (Ramp1) and the second ramp test (Ramp2). 
Presented are (A) Bland– Altman plot for peak VO2 obtained during Ramp1 and Ramp2 [Y- axis = Ramp2 − Ramp1; x- axis = mean of Ramp1 
and Ramp2; dotted lines = mean ± 1.96 × SD; dark solid lines = 0 on the y- axis; light solid lines = mean of Ramp1 − Ramp2] and (b) the 
relationship between peak VO2 obtained during Ramp1 and Ramp2 [the line represents the line of identity (y = x)]. Filled squares (■) 
represent male participants and open diamonds (♢) represent female participants (n = 20)
(a)
(b)
   | 9 of 14
VILLANUEVA et al.
a peak VO2 during Ramp2 that was identified as higher 
(>2.9% difference) compared to Ramp1, and 15% (3 of 20) 
achieved a peak VO2 during Ramp2 that was identified as 
lower (>2.9% difference) compared to Ramp1 (Table 3). 
Results for peak HR, VE, and RER are also presented in 
Table 3.
We recognize the lack of consensus on methodologi-
cal/statistical approaches for confirming VO2max during 
a constant load (verification) test (or any secondary test). 
Therefore, Table 4 provides additional information on 
individual differences/similarities between tests using 
±2  ×  typical error of the two ramp tests (McCarthy 
et al., 2021) and a HR of ±2 bpm (Midgley et al., 2006) or 
±4 bpm (Midgley et al., 2009) from the peak HR from the 
ramp tests. In all instances (study CV, ±2 × typical error, 
HR ±2 or ±4 bpm), when compared to CL110, CL85 had a 
greater percentage of individuals with a constant load test 
that was considered similar to or higher than the ramp.
4 | DISCUSSION
To our knowledge this is the first study to employ a rand-
omized, counterbalanced cross- over design to evaluate the 
utility of constant load tests performed above and below 
ramp- derived peak work rate to serve as a strategy to verify 
a maximal effort and VO2max in healthy older adults. The 
primary finding from this investigation is that in healthy 
older adults, a constant load test performed at a work 
rate slightly below (85%) peak work rate achieved during 
a graded exercise test was more likely to verify VO2max 
as compared to a constant load test performed at a work 
rate above (110%) that achieved during a graded exercise 
test. In addition, our data also indicate that while a second 
identical ramp test could produce a slightly higher peak 
VO2 in a greater number of individuals as compared to the 
constant load test at 85% peak work rate, both strategies 
yield reasonably similar outcomes for verifying VO2max.
Relative to younger adults, little attention has been 
given to the efficacy of a constant load test for verifying a 
maximal effort and VO2max in older adults (Dalleck et al., 
2012; Murias et al., 2018). In this study, we examined to 
what extent a constant load test performed above (110%) 
or below (85%) ramp peak work rate could be used to ver-
ify VO2max in healthy older adults. We specifically chose 
these work rates as they represent the range in intensity 
used in previous studies that used a constant load “verifi-
cation” test (Astorino et al., 2009; Barker et al., 2011; Costa 
et al., 2021; Dalleck et al., 2012; Day et al., 2003; Kuffel 
et al., 2005; Midgley & Carroll, 2009; Murias et al., 2018; 
Niemela et al., 1980; Poole et al., 2008; Rossiter et al., 2006; 
Sawyer et al., 2015; Sedgeman et al., 2013). Consistent with 
many previous studies, we did not identify “group” differ-
ences for peak VO2 achieved between the ramp test and 
the corresponding constant load test, regardless of inten-
sity. However, examination of the individual participant 
Study CV 
(±2.9%)
2 × TE 
(±0.156 L·min−1)
Heart rate 
(±2 bpm)
Heart rate 
(±4 bpm)
Ramp 1 versus Ramp 2
Ind. Similara 
(9/20)
(17/20)
(8/19)
(11/19)
Ind. Highera 
(8/20)
(3/20)
(2/19)
(1/19)
Ind. Lowera 
(3/20)
(0/20)
(9/19)
(7/19)
Ramp versus constant load test at 85%
Ind. Similara 
(15/22)
(21/22)
(10/21)
(12/21)
Ind. Highera 
(4/22)
(1/22)
(7/21)
(7/21)
Ind. Lowera 
(3/22)
(0/22)
(4/21)
(2/21)
Ramp versus constant load test at 110%
Ind. Similara 
(8/20)
(15/20)
(8/19)
(12/19)
Ind. Highera 
(5/20)
(1/20)
(6/19)
(4/19)
Ind. Lowera 
(7/20)
(4/20)
(5/19)
(3/19)
aThe criteria for a similar, higher, or lower value were that the value had to be within or outside (±) the 
study coefficient of variation (CV), 2 × typical error (TE) (McCarthy et al., 2021), or a heart rate within 
2 beats per minute (bpm) (Midgley et al., 2006) or 4 bpm (Midgley et al., 2009) of the peak heart rate 
achieved during the ramp. Ind. Similar, represents the number of participants that achieved a similar 
value (within cut points) during the constant load test versus the associated ramp or for Ramp2 versus 
Ramp1; Ind. Higher, represents the number of participants that achieved a higher value (outside cut 
point) during the constant load test versus the associated ramp or for Ramp2 versus Ramp1; Ind. Lower, 
represents the number of participants that achieved a lower value (outside cut point) during the constant 
load test versus the associated ramp or for Ramp2 versus Ramp1.
TABLE 4 Comparison of various 
individual data “cut points” used in the 
literature to determine verification of 
VO2max
10 of 14 |   
VILLANUEVA et al.
data revealed a greater likelihood for the CL85 test to vali-
date a maximal effort and VO2max as compared to CL110. 
Specifically, only 3 of the 22 participants (~14%) achieved 
a peak VO2 during the CL85 that was lower (outside the 
CV of the two ramp tests) than the value achieved during 
the ramp test. These data indicate that ~86% of the par-
ticipants (19 of 22) achieved a peak VO2 during the CL85 
that was either similar (15 of 22 participants, within the 
CV of the two ramp tests) or higher (4 of 22 participants, 
>CV of the two ramp tests) than that achieved during the 
associated ramp test.
In contrast, 7 of 20 participants (~35%) achieved a peak 
VO2 during the CL110 test that was lower (>CV of the two 
ramp tests) than the value achieved during the ramp test, 
and thus only ~65% achieved a value that was similar (8 of 
20 participants) or higher (5 of 20 participants) than the 
associated ramp test. While we acknowledge previously 
proposed rationale that the constant load “verification” 
test should, theoretically, be conducted at a work rate 
higher than that achieved during the ramp test (e.g., su-
pramaximal) (Poole & Jones, 2017), the present results in-
dicate that a constant load test performed at a work rate of 
110% of ramp peak power may be too high for some older 
adults as a method to verify a maximal effort and VO2max. 
Moreover, the greater agreement in VO2peak between 
the ramp test and CL85 as compared to the ramp test and 
CL110 is also evident through examination of the limits of 
agreement and bias presented in the Bland– Altman plots 
(Figure 1a and 1b), as well as when employing other cut 
points used in the literature (see Table 4). Collectively, our 
findings further support (Iannetta et al., 2020) the use of a 
work rate slightly below peak ramp work rate, as opposed 
to above, when a constant load test to verity a maximal 
effort and VO2max in healthy older adults is warranted. 
Moreover, these results also further support the use of in-
dividual data for assessment of VO2max and comparison 
of constant load “verification” test intensities (Noakes, 
2008).
As expected, the CL110 test elicited a shorter exercise 
duration (mean ~79  s [range, 30– 330  s]) compared to 
CL85 (mean ~185 s [range, 50– 457 s]). Previous research 
in older adults that used a constant load test at 105% of 
ramp peak work rate reported mean durations of ~102 s 
(Murias et al., 2018) and ~150 s (Dalleck et al., 2012). The 
shorter duration observed during CL110 in this study 
may be due to the 5% difference in constant load test 
work rate in participants of approximately the same age 
(Dalleck et al., 2012; Murias et al., 2018). It is also im-
portant to note that the greater likelihood of lower peak 
VO2 values during CL110 could be the result of a reduced 
contribution of the slow component of VO2 (Gaesser & 
Poole, 1996). Specifically, it has been reported that an ex-
ercise duration of >3 min is necessary to observe changes 
in VO2 kinetics that are due to the VO2 slow component 
(Gaesser & Poole, 1996). However, we did not observe 
any significant correlations between exercise time of 
the constant load test and agreement between peak VO2 
achieved during the ramp and corresponding constant 
load test (Figure 3). Interestingly, we did observe that a 
longer time to exhaustion during Ramp110 (thus, higher 
peak power) was more likely to result in a lower peak 
VO2 during CL110. This finding would appear to agree 
with previous work suggesting that a peak VO2 achieved 
during a ramp protocol that resulted in a higher peak 
power was less likely to be validated with a constant load 
effort above the ramp peak power (Iannetta et al., 2020). 
To that end, with the exception of one participant who 
had a history of cycling (highest VO2max), participants 
were relatively unaccustomed to cycling exercise. Thus, 
the lower likelihood of verifying VO2max in these older 
adults when using a constant load test above ramp peak 
work rate may be due to an inability to tolerate the physio-
logical demands of such high work rates for a sufficiently 
long enough time to elicit VO2max. This may also explain 
why nearly 50% (9 of 19) of the participants achieved a 
peak HR during CL110 that was lower (outside the CV of 
the two ramp tests) than that achieved during the associ-
ated ramp.
In this study, participants completed two identi-
cal ramp assessments approximately 1  week apart 
(mean = 9 days). We chose this time frame to provide 
adequate recovery time from the previous test. The mean 
CV observed for peak VO2 between the two ramp tests 
is consistent with ranges identified in previous reports 
(Fielding et al., 1997; Foster et al., 1986; Skinner et al., 
1999), and as discussed above, we utilized the mean 
participant CV (%) from the two identical ramp tests to 
identify individual differences in physiological variables 
between ramp and constant load tests. The design of the 
study also allowed us to examine to what extent a sec-
ond ramp test could be used to assess/verify VO2max in 
older adults. Consistent with previous reports (Foster 
et al., 1986), we did not observe any significant differ-
ences in any physiological variable between the first visit 
(Ramp1) and the second visit (Ramp2). In addition, using 
the CV- derived cut point, the number of participants that 
achieved a similar or higher peak VO2 during Ramp2 
compared to Ramp1 (17/20 participants) was similar to 
that observed when comparing CL85 to the ramp (19/22 
participants). However, when compared to the ramp ver-
sus constant load test comparisons, more participants 
achieved a higher peak VO2 during Ramp2 compared to 
Ramp1 (40%; 8/20 participants). Importantly, these dis-
crepancies in peak VO2 achieved during the ramp in the 
first and second experimental trial did not impact the 
comparison between the associated ramp and constant 
   | 11 of 14
VILLANUEVA et al.
load tests. Not only was the study counter- balanced, 
but among participants who completed both trials and 
achieved a peak VO2 during a constant load test that was 
different compared to the associated ramp test, there was 
a similar number of participants who achieved a different 
(higher or lower) peak VO2 during the constant load test 
during the first (higher value, n = 5; lower value, n = 4) 
and during the second experimental trial (higher value, 
n = 4; lower value, n = 6). Collectively, these data indi-
cate that some individuals may not be accustomed to the 
maximal intensity of exercise, the mode of exercise, or 
perhaps the breathing apparatus (Poole & Jones, 2012). 
Moreover, the results of this study indicate that a famil-
iarization trial or second ramp could also increase the 
accuracy of VO2max assessments in some older adults, 
perhaps for a slightly greater number of individuals as 
compared to the use of a constant load test.
Peak HR was not different during the ramp test and 
either constant load test intensity. This finding contrasts 
with the results of a previous study with older adults that 
found a significantly higher peak HR during a ramp test as 
compared to a supramaximal verification test (105%) and 
submaximal (85%) verification test (Murias et al., 2018), al-
though the magnitude of difference in that study (Murias 
et al., 2018) was extremely small (1– 2  bpm). Moreover, 
similar to VO2max discussed above, individual data in-
dicate that a greater number of participants achieved a 
similar or higher peak HR during CL85 versus the ramp 
as compared to CL110 versus the ramp (86% vs. 53%). In 
addition, the individual data and visual inspection of the 
Bland– Altman plots suggest a greater likelihood for par-
ticipants to achieve a lower peak HR during CL110 ver-
sus the ramp as compared to CL85. Together with the VO2 
data, these peak HR data further support the incorpora-
tion of a constant load test performed slightly below peak 
ramp work rate for verification of maximal values in older 
adults.
We recognize that previous studies have utilized 
rest periods as short as 3  min and as long as a full 
week between ramp and constant load verification 
tests (Astorino et al., 2009; Barker et al., 2011; Dalleck 
et al., 2012; Day et al., 2003; Hawkins et al., 2007; Kuffel 
et al., 2005; Leicht et al., 2013; Midgley & Carroll, 2009; 
Midgley et al., 2006; Murias et al., 2018; Niemela et al., 
1980; Nolan et al., 2014; Poole et al., 2008; Rossiter et al., 
2006; Sawyer et al., 2015; Scharhag- Rosenberger et al., 
2011; Sedgeman et al., 2013; Weatherwax et al., 2016), 
and thus we cannot extend our findings to situations 
that may utilize different rest periods between tests. 
However, we specifically employed a 10- min active rest 
period between the end of the ramp test and the initia-
tion of the constant load test as this timeframe is likely 
to be more practical for future research and clinical 
practice as participants would not be required to come 
back for testing at a later time or date. In addition, it 
is possible that our findings may have been influenced 
by the duration of the ramp test (Iannetta et al., 2020). 
Similarly, some reports indicate that a valid VO2max is 
achieved with a ramp test of at least 8 min (Buchfuhrer 
et al., 1983), although this notion has been challenged 
(Midgley et al., 2008). Finally, we acknowledge that 
the necessity of verification tests has been questioned 
(Murias et al., 2018; Wagner et al., 2021), perhaps on the 
basis that a high percentage of verification tests yield 
peak VO2 values that are considered similar to the ramp 
tests. Indeed, if the graded exercise test was a maximal 
effort, then in theory the ramp and constant load tests 
should yield similar values. In addition, it is important 
to note that previous studies (see (Costa et al., 2021)), as 
well as data from the current investigation, demonstrate 
that not all ramp tests will yield maximal VO2 values (or 
values that are similar between the ramp and secondary 
verification test). Importantly, those ramp efforts that 
do and do not produce maximal values could not be 
identified without employing a secondary test to verify 
the results. Future investigators and/or clinicians will 
need to determine, for their specific use, the necessity 
to obtain an accurate measurement of VO2max and to 
what extent a value requires “verification” using a sin-
gle visit or multiple visit approach.
In conclusion, these findings have implications for 
the evaluation of VO2max of older adults in both a re-
search and clinical setting. In particular, given the over-
whelming data to suggest VO2max/cardiorespiratory 
fitness is perhaps the most powerful predictor of cardio-
vascular disease risk (Kokkinos et al., 2010; Myers et al., 
2002; Ross et al., 2016), identifying strategies to obtain 
an accurate assessment of VO2max in older adults will 
serve to better identify individuals at risk for cardiovas-
cular disease as well as those with increased risk of mor-
bidity and mortality. Specifically, our data indicate that 
when verification of maximal values is warranted in a 
single testing session, a constant load test performed at 
85% of ramp peak power is more likely to verify a max-
imal effort and VO2max in older adults as compared to 
a constant load test at 110% ramp peak power. On the 
other hand, in situations where multiple participant vis-
its are feasible, performing an additional ramp test may 
also serve to verify VO2max, and could potentially lead 
to higher values in a slightly greater number of partici-
pants. However, the logistics and associated participant 
burden of recovery times between tests in a single ses-
sion and/or multiple visits must be considered in the ap-
plication of constant load testing to verify VO2max in the 
real- world settings (especially clinical environments and 
clinical populations).
12 of 14 |   
VILLANUEVA et al.
ACKNOWLEDGMENTS
The authors thank the participants for their time. I.R.V., 
S.S.A., G.A.G., and J.M.D. designed research; I.R.V., 
J.C.C., S.M.M., T.M.J., S.L.W., S.S.A., G.A.G., and J.M.D. 
conducted research; I.R.V. and J.M.D. analyzed data and 
performed statistical analysis; I.R.V. and J.M.D. wrote 
the manuscript and have primary responsibility for final 
content; all authors approved the final version of the 
manuscript.
DISCLOSURES
The authors have no conflict of interest to declare.
ORCID
Jared M. Dickinson 
 https://orcid.
org/0000-0003-3142-938X 
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How to cite this article: Villanueva, I. R., 
Campbell, J. C., Medina, S. M., Jorgensen, T. M., 
Wilson, S. L., Angadi, S. S., Gaesser, G. A., & 
Dickinson, J. M. (2021). Comparison of constant- 
load exercise intensity for verification of maximal 
oxygen uptake following a graded exercise test in 
older adults. Physiological Reports, 9, e15037. 
https://doi.org/10.14814/ phy2.15037

Comparison of constant load exercise intensity for verification of maximal oxygen uptake following a graded exercise test in older adults.
Villanueva, Ian R,Campbell, John C,Medina, Serena M,Jorgensen, Theresa M,Wilson, Shannon L,Angadi, Siddhartha S,Gaesser, Glenn A,Dickinson, Jared M