Are fixed-rate step tests medically safe for assessing physical fitness?

Abstract

Maximal oxygen uptake (VO(2max)) can be predicted by fixed-rate step tests. However, it remains to be analyzed as to what exercise intensities are reached during such tests to address medical safety. In this study, we compared the physiological response to a standardized fixed-rate step test with maximal cardiopulmonary exercise testing (CPET). One hundred and thirteen healthy adults executed a maximal CPET on bike, followed by a standardized fixed-rate step test 1 week later. During these tests, heart rate (HR) and VO(2) were monitored continuously. From the maximal CPET, the ventilatory threshold (VT) was calculated. Next, the physiological response between maximal CPET and step testing was compared. The step test intensity was 85 ± 24% CPET VO(2max) and 88 ± 11% CPET HR(max) (VO(2max) and HR(max) were significantly different between CPET and step testing; p < 0.01). In 41% of the subjects, step test exercise intensities >95% CPET VO(2max) were noted. A greater step testing exercise intensity (%CPET VO(2max)) was independently related to higher body mass index, and lower body height, exercise capacity (p < 0.05). Standardized fixed-rate step tests elicit vigorous exercise intensities, especially in small, obese, and/or physically deconditioned subjects. Medical supervision might therefore be required during these tests.

Full text

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ORIGINAL ARTICLE
Are fixed-rate step tests medically safe for assessing physical
fitness?
Dominique Hansen•Nele Jacobs•Steven Bex•
Goedele D’Haene•Paul Dendale•Neree Claes
Received: 24 December 2010/Accepted: 18 February 2011
? Springer-Verlag 2011
Abstract
dicted by fixed-rate step tests. However, it remains to be
analyzed as to what exercise intensities are reached during
such tests to address medical safety. In this study, we
compared the physiological response to a standardized
fixed-rate step test with maximal cardiopulmonary exercise
testing (CPET). One hundred and thirteen healthy adults
executed a maximal CPET on bike, followed by a stan-
dardized fixed-rate step test 1 week later. During these
tests, heart rate (HR) and VO2were monitored continu-
ously. From the maximal CPET, the ventilatory threshold
(VT) was calculated. Next, the physiological response
between maximal CPET and step testing was compared.
The step test intensity was 85 ± 24% CPET VO2maxand
88 ± 11% CPET HRmax(VO2maxand HRmaxwere signif-
icantly different between CPET and step testing; p\0.01).
In 41% of the subjects, step test exercise intensities[95%
CPET VO2maxwere noted. A greater step testing exercise
intensity (%CPET VO2max) was independently related to
Maximal oxygen uptake (VO2max) can be pre-
higher body mass index, and lower body height, exercise
capacity (p\0.05). Standardized fixed-rate step tests elicit
vigorous exercise intensities, especially in small, obese,
and/or physically deconditioned subjects. Medical super-
vision might therefore be required during these tests.
Keywords
Physical fitness
Exercise testing ? Step test ? Medical safety ?
Introduction
It is established that regular physical activity and/or exer-
cise training lowers chronic disease incidence and pre-
mature mortality risk in humans (Renehan and Howell
2005). As a result, the importance of exercise in the pre-
vention of cancer, diabetes, and cardiovascular disease is
acknowledged (Renehan and Howell 2005).
In order to provide adequate individual exercise pre-
scription when aiming to increase physical activity, the
physical fitness should be assessed. In this regard, maximal
oxygen uptake (VO2max), which is considered the gold
standard surrogate for maximal exercise capacity, should
be measured. Unfortunately, due to time investment, costs
of equipment, and/or required technical skills, some (non-
medical) healthcare professionals, institutes, and/or labo-
ratories are unable to execute ergospirometry tests. As a
result, these are in need of physical fitness tests with lim-
ited time investment, need for equipment, and technical
skills.
Decades ago, fixed-rate step tests were introduced
(McArdle et al. 2010). In these tests, the patient steps up
and down a bench at a fixed rate for a few minutes. Next,
the test duration as well as heart rate at the end of testing
and during recovery is used to predict VO2max.These tests
Communicated by Susan A. Ward.
D. Hansen (&) ? P. Dendale
Jessa Hospital/Heart Centre Hasselt, Rehabilitation and Health
Centre, Stadsomvaart 11, Hasselt, Belgium
e-mail: Dominique.hansen@jessazh.be
D. Hansen ? P. Dendale
Rehabilitation and Healthcare Research Centre,
Department Healthcare, PHL-University College,
Hasselt, Belgium
D. Hansen ? N. Jacobs ? S. Bex ? G. D’Haene ? P. Dendale ?
N. Claes
Faculty of Medicine, Hasselt University, Diepenbeek, Belgium
123
Eur J Appl Physiol
DOI 10.1007/s00421-011-1886-3

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have been shown to provide an adequate prediction of
VO2maxin individuals free from chronic disease (Siconolfi
et al. 1985), and are easy to use (Petrella et al. 2001, 2003).
However, what percentage of the actual VO2maxis reached
during such fixed-rate step tests remains to be studied.
Previous studies have assessed VO2 during stepping
exercise, but did not compare this to VO2max reached
during cardiopulmonary exercise testing (Buckley et al.
2004; Jones et al. 1987; Olson et al. 1991; Richardson
and Hardman 1989; Stanforth et al. 1993; Thomas et al.
1993). It might be argued that probably low-to-moderate
exercise intensities (\75% VO2max) are elicited during
fixed-rate step testing (Noonan and Dean 2000), thereby
diminishing the need for medical supervision. As a result,
it is speculated that non-medical healthcare professionals
could execute these tests in the absence of a physician.
On the other hand, vigorous-intensity physical exercise
([75% VO2max) significantly increases the risk for myo-
cardial ischemia, malignant cardiac arrhythmias, acute
myocardial infarction and, in rare occasions, sudden
death, in individuals unaccustomed to physical exercise
(Albert et al. 2000; Bartsch 1999; Thompson et al. 2007).
As a result, clinical guidelines declare that medical
supervision is required during exercise tests with (near)
maximal effort (Myers et al. 2009). The elicited exercise
intensity during step testing procedures therefore requires
investigation.
In this study, we assessed the physiological response to a
standardized fixed-rate step test in a large mixed population
of healthy individuals, and compared this to the response to
maximal cardiopulmonary exercise testing. We hypothe-
sized that during step tests low-to-moderate exercise
intensities (55–75% VO2max) are elicited, indicating that
these tests can be employed safely without medical
supervision.
Materials and methods
Subjects
One hundred and thirteen (#: 60, see Table 1) subjects,
between age 23 and 75 years, were included in this study.
These subjects were invited to participate in this study by
local advertisement. All subjects were informed about the
nature and risks of this study and provided written
informed consent. The ethical committee for human
research from Jessa Hospital approved the study protocol.
Subjects were excluded from participation in the study in
case of any acute and/or chronic disease, and/or orthopedic
injury/dysfunction, and in case of heart rate-altering phar-
macologic treatment. Subjects presenting myocardial
ischaemia (ST segment depression[0.1 mV and/or angina
pectoris) and/or severe ventricular arrhythmias during
exercise testing were excluded.
Study design
Following inclusion, subjects filled out a physical activ-
ity questionnaireand performed
exercise test and step test on 2 separate days interspersed
by a 1 week recovery. The cardiopulmonary exercise test
was always executed first to assess myocardial function
by ECG, followed by the step test. The same investi-
gator performed all measurements at the same time of
the day.
a cardiopulmonary
Table 1 Subject characteristics
Mean ± SDRange
General characteristics
Gender (% male) 52
Age (years)45 ± 13 23–75
Body weight (kg) 71 ± 1343–106
Body height (m)
Body mass index (kg/m2)
1.72 ± 0.11.54–1.94
24 ± 316–34
Exercise capacity
VO2max(L/min)
%predictedaVO2max
Wmax
HRmax(bpm)
% predicted HRmax
Ventilatory threshold (L/min)
2.6 ± 0.9 0.9–4.9
114 ± 31 63–215
216 ± 7890–400
172 ± 14 145–206
98 ± 6 90–114
1.6 ± 0.70.4–3.7
Ventilatory threshold/VO2maxratio (%)
Step test data
61 ± 11 38–84
Resting heart rate 89 ± 1555–138
HRmax(bpm)
% predicted HRmax
HR recovery after 1 min (bpm)
151 ± 20 108–197
86 ± 12 58–116
108 ± 2557–160
HR recovery after 2 min (bpm) 94 ± 2146–152
HR recovery after 3 min (bpm)89 ± 1853–137
Test duration (sec)283 ± 49 45–300
RPE Borg
Physical activityb
13 ± 2 7–20
Total physical activity (kcal/week)510 ± 3510–1782
Moderate-intensity physical activity
(kcal/week)
396 ± 2890–1373
High-intensity physical activity
(kcal/week)
119 ± 1360–624
VO2max, maximal oxygen uptake; Wmax, maximal cycling power
output; HRmax, maximal heart rate; RPE, ratings of perceived exertion
aBased on formulae from Fairbarn et al. (1994)
bEstimation based on IPAQ questionnaire
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Measurements
Physical activity level
The International Physical Activity Questionnaire (Craig
et al. 2003) was used to assess time engaged in moderate-
and high-intensity physical activity in the last month before
this study. Cut-off limits for exercise intensity (moderate
vs. high intensity) were based on the ventilatory response
during exercise. If the subject was able to talk during
exercise without experiencing dyspnea, such exercise was
considered as moderate intense. If the subject was no
longer able to talk during exercise without experiencing
dyspnea, such exercise was considered as high intense.
Mean caloric expenditure was calculated by the sum of
total physical activity duration, and correct this for body
weight and applied exercise intensity.
Cardiopulmonary exercise capacity
All subjects performed a maximal incremental 1 min
stage cardiopulmonary cyclo ergometer exercise test
(CPET) (Buchfuhrer et al. 1983). Subjects were stimu-
lated to achieve maximal exertion, and subjective symp-
toms (general/muscle fatigue, dyspnea) were primarily
used to consider their effort (Poole et al. 2008). Sec-
ondary, objective criteria were then used to assess whe-
ther maximal exercise effort during exercise testing was
achieved: respiratory exchange ratio [1.10 and/or heart
rate [90% of maximal predicted value. During the cyclo
ergometer test, an electronically braked Ergo 1,500 cycle
(ErgoFit?, Pirmasens, Germany) was used. The cycling
frequency was set at 70 rpm and the test was ended when
the subject failed to maintain a cycling frequency of at
least 60 rpm (Fletcher et al. 2001). At the morning of
every test day, an automatic gas (software program of the
ergospirometry device automatically tested the atmo-
spheric air for oxygen, nitrogen, and carbon dioxide
content, and a certified mix of gases) and manual volume
calibration (with 2 L syringe) was performed. During the
exercise tests, pulmonary gas exchange analysis was
performed by a cardiopulmonary ergospirometry device
(Schiller CS200?, Schiller AG, Switzerland). Oxygen
uptake (VO2) and carbon dioxide output (VCO2) were
collected breath-by-breath and averaged every 10 s. Pre-
dicted VO2maxwas calculated from age, gender, height,
and weight (Fairbarn et al. 1994), and compared to the
actually achieved VO2max (expressed in % predicted
VO2max). Ventilatory threshold (VT) was calculated by
V-slope method (Beaver et al. 1986), and curves were
carefully reviewed by the investigators, as executed in
previous studies by our laboratory (Hansen et al. 2007).
Using a 12-lead ECG device, heart rate (HR) was
monitored and averaged every 10 s. Maximal cycling
power output (Wmax) was reported.
Step test
The step test was modified from earlier procedures (Pet-
rella et al. 2003). The step test consisted of stepping up
and down a platform at a rate controlled by a metronome
(90 beats/min, corresponding to 22.5 steps/min). Each
beat initiates the movement of one leg up or down the
platform. The stepping period lasted for 5 min. The height
of the platform was determined according to patients’
body height. For individuals up to 170 cm a platform of
33 cm was used. For individuals with a body height
above 170 cm a platform of 40 cm was used. The step-
ping rate and bench height was comparable to those used
in previous studies. The heart rate was continuously
monitored by a commercially available ambulatory sys-
tem (Polar, Oy, Finland). The heart rate was recorded
immediately after step testing, and in sitting position
between 1 and 1:30 min after completing the step test,
between 2 and 2:30 min, between 3 and 3:30 min. In
addition to heart monitoring, pulmonary gas exchange
analysis was performed during the step test by a cardio-
pulmonary ergospirometry
Schiller AG, Switzerland). On the morning of every test
day, an automatic gas and volume calibration was per-
formed (with similar methodology as mentioned in the
section of ‘cardiopulmonary exercise capacity’). Oxygen
uptake (VO2) was collected breath-by-breath and averaged
every 10 s. VO2was measured and averaged during the
final min during step testing. From this measurement, the
step testingexercise intensity
expressed in percentages (%CPET VO2max) = (VO2step
test/VO2max CPET) 9 100. At the end of the step test,
ratings of perceived exertion were immediately scored by
a 20-point Borg scale.
device (SchillerCS200?,
was calculatedand
Statistical analysis
Data are expressed as means ± SD. Statistical significance
was set at p\0.05 (2-sided). We compared the maximal
physiological response (HR and VO2) between CPET and
step test by paired sample t tests. Step test exercise inten-
sity was compared between genders by one-way ANOVA.
Univariate correlations were calculated between step test-
ing exercise intensity (%CPET VO2max) and subject char-
acteristics (age, body mass index, exercise capacity, body
height, ratings of perceived exertion, and self-reported
physical activity). Multivariate regression analysis was
executed to examine the relationship between %CPET
VO2max (independent variable) and age, gender, body
height, body mass index, VO2max, VT, and high-intensity
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physical activity (dependent variables). These dependent
variables were selected based on their significant univariate
correlations with %CPET VO2max. All calculations were
performed using the Statistical Package for the Social
Sciences, version 15.0.
Results
Subjects
Middle-aged (45 ± 13 years), physically active, normal-
weight (body mass index of 24 ± 3 kg/m2) subjects were
included, with a large range for these parameters (see
Table 1). None of the subjects developed myocardial
ischaemia and/or severe ventricular arrhythmias during
exercise testing on bike.
Physiological response to CPET and step test
Based on CPET VO2max(114 ± 31% of predicted value),
the subjects had a normal maximal exercise capacity (see
Table 1). In extent, VT occurred at 61 ± 11% of the CPET
VO2max, which is considered normal. Subjects reached
98 ± 6% of their maximal predicted HR, indicating that
subjects cycled until exhaustion during CPET.
As result of the fixed-rate step test, HR rose from
89 ± 15 bpm at rest up to 151 ± 20 bpm (see Table 1). Of
the subjects, 12% did not achieve the total step test time
(5 min) because of physical exhaustion. Subjects scored an
average RPE Borg of 13 ± 2 immediately after the step
test.
Comparison between CPET and step test
The step test VO2 (2.0 ± 0.6 L/min, 28.7 ± 5.5 mL/kg/
min) was significantly lower when compared to CPET
VO2max (2.6 ± 0.9 L/min, 36.4 ± 11.7 mL/kg/min) (p\
0.01) (see Fig. 1). The step test VO2 was on average
85 ± 24% of CPET VO2max and 88 ± 11% of CPET
HRmax. In 41 and 67% of the subjects, step test exercise
intensities [95 and [75% CPET VO2max, respectively,
were noted.
Univariate correlations
A significant univariate correlation was found between step
test VO2and CPET VO2max(r = 0.54, p\0.01). A greater
step testing exercise intensity (%CPET VO2max) was sig-
nificantly related to higher age and body mass index, and
lower body height, total and high-intensity physical activ-
ity, VT, and VO2max(p\0.05) (see Table 2). A significant
correlation was found between step test exercise intensity
and RPE Borg (p\0.01). In addition, step testing exercise
intensity was significantly different between males and
females (79 ± 24 vs. 91 ± 21% CPET VO2max, respec-
tively; p\0.01).
Multivariate regression analysis
A greater step testing exercise intensity (%CPET VO2max)
was significantly and independently related to higher body
mass index,andlowerbody
(p\0.05). Age, gender, and high-intensity physical
height, VT,
VO2max
0
10
20
30
40
50
60
VO2(mL/kg/min)
0
0.5
1
1.5
2
2.5
3
3.5
4
VO2(L/min)
VO2maxCPET
VO2step test
VO2maxCPET
VO2step test
A
B
Fig. 1 Physiological response to maximal cardiopulmonary exercise
test and step test. a VO2expressed in absolute values. b VO2corrected
for body weight. *Significantly different between tests (p\0.05).
VO2, oxygen uptake; CPET cardiopulmonary exercise test
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activity were no longer significantly related to %CPET
VO2max.
Discussion
In this study, we examined the physiological response to a
standardized fixed-rate step test in a mixed population of
healthy individuals, and compared this to the response from
maximal cardiopulmonary exercise testing (CPET). By
doing so, we examined whether these tests can be
employed safely in healthy adults (low risk for adverse
cardiovascular events). From this study, two important
findings emerged. First, standardized fixed-rate step tests
elicit vigorous exercise intensities. Second, greater step test
intensities were noted in small, obese, and/or physically
deconditioned subjects.
Vigorous exercise intensities were elicited during stan-
dardized fixed-rate step tests: the step test exercise intensity
was on average *85% of CPET maximal oxygen uptake
(VO2max). Moreover, in 41 and 67% of the subjects, step
test exercise intensities [95 and [75% CPET VO2max,
respectively, were noted. These results are in clear contrast
with the widely upheld belief that fixed-rate step tests elicit
exerciseintensities up to
VO2max.(Noonan and Dean 2000) Hence, it is therefore
assumed that medical supervision is not required during
these exercise tests. Based on these assumptions, fixed-rate
step tests are currently mainly executed by non-medical
personnel, or in physician offices without medical super-
vision. On the other hand, vigorous-intensity physical
exercise ([75% VO2max) significantly increases the risk for
maximally
*75%of
acute myocardial infarction and, in rare occasions, sudden
death, in individuals unaccustomed to physical exercise
(Albert et al. 2000; Bartsch 1999). This might be related to
acute platelet activation and aggregation, increased for-
mation of thrombin and fibrin, augmentation of blood
catecholamine concentrations, increased endothelial shear
stress triggering fissure or rupture of plaques (Bartsch
1999; Cadroy et al. 2002; Hilberg et al. 2008; Ikarugi et al.
2003). In case of coronary artery disease patients, the risk
for acute myocardial infarction and/or malignant ventric-
ular arrhythmias could be related to an insufficient coro-
nary blood supply during increased myocardial work
(Thompson et al. 2007). According to our results, 67% of
the subjects achieved exercise intensities above this
threshold during step testing. Clinical guidelines declare
that medical supervision is required during exercise tests
with such intensities (Myers et al. 2009).
Even though there might be an increased relative risk for
adverse cardiovascular events during step testing, the
absolute risk might be low. The combined morbidity and
mortality rate during maximal cardiopulmonary exercise
testing is about 0.2% (Myers et al. 2009). Statistics about
the morbidity and mortality rate during step testing are, to
our knowledge, absent.
Because vigorous exercise intensities were elicited dur-
ing step testing, test methodology modifications might be
required to lower physical exertion. For this purpose, it
might be suggested to lower step height (even though we
already adjusted step height according to body height in our
study), slow stepping rate, and/or allow the subject to self-
select the stepping rate (Olson et al. 1991; Petrella et al.
2001; Stanforth et al. 1993; Thomas et al. 1993). In this
regard, further study indeed noted lower cardiovascular/
physiological responses during stepping activity when
lowering stepping rate/height (Buckley et al. 2004; Olson
et al. 1991; Petrella et al. 2001; Stanforth et al. 1993).
Even though previous investigations have examined the
validity, reproducibility, and applicability of step tests for
the estimation of VO2max(Siconolfi et al. 1985; Petrella
et al. 2001, 2003), and other studies have assessed VO2
during step testing/stepping exercise (Buckley et al. 2004;
Jones et al. 1987; Olson et al. 1991; Richardson and
Hardman 1989; Stanforth et al. 1993; Thomas et al. 1993),
the elicited relative exercise intensity (%CPET VO2max)
during these tests remained to be shown. As a result, we
were not able to contrast our findings with those from
previous studies.
Greater step test exercise intensities (%CPET VO2max)
were achieved in small, obese, and/or physically decondi-
tioned subjects. Consequently, in subjects with these
characteristics, the medical safety of fixed-rate step testing
might be questioned further. Thomas et al. (1993) noted
correlations between age, leg length, aerobic fitness, and
Table 2 Univariate correlations between step test exercise intensity
(%CPET VO2max) and subject characteristics
Step test exercise intensity
(%CPET VO2max)
rp value
Age0.220.02
\0.01
0.36
\0.01
\0.01
\0.01
\0.01
0.01
Body height-0.26
Body weight0.09
Body mass index0.31
VO2max
Wmax
Ventilatory threshold
-0.67
-0.64
-0.64
Total physical activity-0.25
Moderate-intensity physical activity-0.110.28
\0.01
\0.01
High-intensity physical activity-0.37
RPE Borg during step test0.59
VO2max, maximal oxygen uptake; Wmax, maximal cycling power
output; RPE, ratings of perceived exertion
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VO2during stepping in 121 individuals. Stanforth et al.
(1993) revealed in 28 females that a decreased leg length
and/or increased fat-free mass increased VO2during step-
ping activity. Jones et al. (1987) found a significant cor-
relation between step test VO2and body weight, height in
53 participants. On the other hand, Buckley et al. (2004)
failed to observe correlations between subject characteris-
tics and stepping activity VO2, except for body height, in
13 subjects.
It should be mentioned that during step testing one leg is
tested more vigorously (the leg that steps up) as opposed to
the other leg (the leg that follows the step-up). Such dif-
ference in exercise intensity between legs is not present
during exercise testing on bike. It follows that when severe
differences in muscle strength and/or endurance are present
between the legs (for example as result of unilateral knee
prosthesis, neurologic disease), the outcome between step
testing and testing on bike could be different. In the present
study, subjects with lower extremity disease/anomalies
were excluded.
From this study, an important clinical implication
might emerge. When executing fixed-rate step tests to
estimate VO2max, medical supervision (or immediate
physician presence) seems required to optimize patient
safety. This seems especially the case in small, obese,
and/or physically deconditioned subjects. Moreover, it
might be suggested to execute continuous ECG monitor-
ing during step testing, in order to detect malignant car-
diac arrhythmias and/or myocardial ischemic responses.
Because of the lack of a gradual workload increase, such
complications might be prevalent. Since medical super-
vision, and assessment of medical safety (such as ECG
monitoring), seems warranted during step testing, it might
be argued that these tests can no longer be regarded as
easy and inexpensive.
This study might be limited by the lack of measurements
of physiological parameters directly addressing adverse
cardiovascular event risk (platelet activation and aggrega-
tion, blood pressure, and/or blood catecholamine concen-
trations) during step testing. Therefore, further study might
be required to assess these parameters during fixed-rate
step testing. Moreover, we used a questionnaire to assess
physical activity, as well as the intensity of physical
activity. It might be more accurate to use objective physical
activity assessment instruments (heart rate monitoring,
accelerometry).
In conclusion, standardized fixed-rate step tests elicited
vigorous exercise intensities in healthy individuals, espe-
cially in small, obese, and/or physically deconditioned
subjects. Therefore, medical supervision during step testing
seems required.
Ethical standards. The experiments comply with the
current laws of the country in which they were performed.
Acknowledgments
chair ‘De Onderlinge Ziekenkaspreventie’, and by a research grant
from Hartcentrum Hasselt, Belgium.
This study was partially funded by the scientific
Conflict of interest
of interest.
The authors declare that they have no conflict
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