RELATIONSHIP BETWEEN %HEART RATE RESERVE AND %VO2 RESERVE
DURING ELLIPTICAL CROSSTRAINER EXERCISE
1Human Performance Laboratory, University of Wisconsin - Eau
Claire, Eau Claire, WI USA
2Exercise Physiology Laboratories, University of New Mexico, Albuquerque,
31 July 2006
Journal of Sports Science and Medicine (2006) 5, 662 - 671
Google Scholar for Citing Articles
primary purpose of the study was to determine the relationships between
%HRR vs. %VO2R and %HRR vs. %VO2max during maximal
elliptical crosstrainer (ECT) exercise. A secondary aim was to compare
the %HRR vs. %VO2R and %HRR vs. %VO2max relationships
between maximal ECT and treadmill (TM) exercise. Adult subjects (n
= 48) completed a maximal exercise test on the ECT, with a subgroup
(N = 24) also performing a maximal exercise test on the TM. Continuous
HR and VO2 data were analyzed via linear regression to
determine y-intercept and slope values for %HRR vs. %VO2R
and %HRR vs. %VO2max. Student t-tests were used to determine
whether the mean y-intercept and slope values differed from the line
of identity (y-intercept = 0, slope = 1). For each group, both the
y-intercept and slope for %HRR vs. %VO2R fit the line of
identity. Conversely, for all groups both the y-intercept and slope
for %HRR vs. %VO2max were significantly different (p <
0.001) from the line of identity (y-intercept ≠ 0, slope ≠
1). In comparing the regressions of %HRR vs. %VO2R between
exercise modes, there were no significant differences (p > 0.05)
for either y-intercept (ECT = 0.3 vs. TM = -0.3, p = 0.435) or slope
(ECT = 1.01 vs. TM = 1.00, p = 0.079) values. In agreement with previous
research on TM and cycle exercise, it was found that %HRR is more
closely aligned with %VO2R, rather than %VO2max
during ECT exercise. Additionally, it was found that the regressions
of %HRR vs. %VO2R and %HRR vs. %VO2max were
equivalent between the ECT and TM.
WORDS: Exercise mode, regression, exercise prescription.
The ability to accurately prescribe exercise intensity is a fundamental
aspect of exercise physiology, with exercise professionals frequently
relying upon multiple methods to establish target workloads, including
percentages of maximal heart rate (%HRmax), heart rate
reserve (%HRR), and maximal oxygen uptake (%VO2max) (ACSM-American
College of Sports Medicine, 1995).
Traditionally, it was accepted that the %HRR was equivalent to %VO2max
(American College of Sports Medicine, 2006),
however, more recent research has demonstrated that %HRR is more
clearly aligned with percent oxygen uptake reserve (%VO2R).
These findings have been reported in both young, healthy populations
(Swain and Leutholtz, 1997;
Swain et al., 1998)
and older, diseased populations (Brawner et al., 2002).
Swain and Leutholtz, 1997
first reported that %HRR is equivalent to %VO2R, and
not %VO2max, during cycling exercise in healthy, young
males and females. These findings were confirmed by Swain et al.,
during treadmill exercise in a young, healthy population, although
the regression between %HRR and %VO2R differed statistically
from the line of identity. Similarly, Brawner et al., 2002
demonstrated that the relationship between %HRR and %VO2R,
though statistically different, is closer to the line of identity
than %HRR and %VO2max during treadmill exercise in cardiac
patients. The authors suggested that there may be a mode effect
(treadmill vs. cycle), which would explain the line of identity
differences between studies. However, they added that work by Davis
and Convertino, 1975
argues against a mode effect, although to our knowledge, no research
exists that directly compares the relationship between %HRR and
%VO2R in different exercise modes.
While the treadmill and cycle ergometer are among the most common
forms of exercise, the elliptical crosstrainer has become increasingly
popular in recent years as an alternative aerobic exercise modality
in fitness centers and rehabilitation facilities (Green et al.,
To date, there has been limited research on this modality of exercise,
however, results from one study suggest there are similar heart
rate responses to elliptical crosstrainer exercise compared to treadmill
exercise at equivalent rating of perceived exertion (RPE) levels
(Green et al., 2004).
The increasing popularity of elliptical crosstrainer exercise coupled
with the need to better understand the relationships between %HRR
vs. %VO2R and %HRR vs. %VO2max for accurate
exercise prescriptions prompted the present investigation.
The primary purpose of the study was to determine the relationships
between %HRR vs. %VO2R and %HRR vs. %VO2max
during maximal elliptical crosstrainer exercise. It was hypothesized
that %HRR is equivalent to %VO2R, and not %VO2max.
Although previous research (Brawner et al., 2002;
Swain and Leutholtz, 1997;
Swain et al., 1998)
has established that %HRR is more closely aligned to %VO2R,
rather than %VO2max, only one study (Swain and Leutholtz,
has reported that the y-intercept and slope for %HRR vs. %VO2R
fit the line of identity (p > 0.05). Consequently, although using
%HRR vs. %VO2R for exercise prescription purposes may
be preferred to %HRR vs. %VO2max, there still may be
measurable error when using this approach. Furthermore, it remains
unclear whether the exercise mode influences the nature of the %HRR
vs. %VO2R and %HRR vs. %VO2max relationships.
A secondary purpose of the study was to compare the %HRR vs. %VO2R
and %HRR vs. %VO2max relationships between maximal elliptical
crosstrainer and treadmill exercise. It was hypothesized that there
would be no significant differences in the relationships between
the two exercise modalities.
A total of 48 subjects (24 males, 24 females) familiar with elliptical
crosstrainer and treadmill exercise were recruited from the faculty
and student population of the university as well as the surrounding
community. Subjects provided informed written consent and completed
a health history questionnaire prior to participating in the study.
All subjects were apparently healthy as defined by the ACSM (2006).
Furthermore, all subjects indicated on the health history questionnaire
that they satisfied the minimum requirements for a moderate level
of aerobic activity on a regular basis (at least 3 times per week)
as classified by the ACSM (2006). The university's Human Subjects
Institutional Review Board approved this study. Subject characteristics
are presented in Table 1.
Subjects were instructed to avoid eating food four hours prior to
testing and to refrain from strenuous exercise 12 hr prior to testing.
Subjects were weighed to the nearest 0.1 kg on a medical grade scale
and measured for height to the nearest 0.5 cm using a stadiometer.
The average temperature throughout testing was 21.4 ± 0.5 oC.
Percent fat was determined via skinfolds (Jackson and Pollock, 1985).
Skinfold thickness was measured to the nearest ± 0.5 mm using a
Lange caliper (Cambridge Scientific Industries, Columbia, Maryland,
USA). All measurements were taken on the right side of the body
using standardized anatomical sites (three-site) for both men and
women. These measurements were performed until two were within 10%
of each other.
Each subject (n = 48) completed an incremental, maximal exercise
test in 1-min stages on the same Precor EFX 546 Elliptical Fitness
Crosstrainer (Precor Inc., Woodinville, WA). The workload components
of the elliptical crosstrainer include cadence, incline, and resistance,
which range from 1-20 units, 1-20 units, and 0-300 strides?min-1,
respectively. The stride length of the Precor EFX 546 Elliptical
Fitness Crosstrainer model used in the present study was 48 cm.
According to a Latin Squares design, every other male (n = 12) and
female subject (n = 12) from the total subject pool (Figure
1) was selected to also perform an incremental, maximal exercise
test in 1-min stages (Modified Balke) on a motorized treadmill (SensorMedics
2000, Yorba Linda, CA). For the subjects who performed maximal elliptical
crosstrainer and treadmill tests, testing sessions were separated
by at least 24 hr to minimize subject fatigue. Additionally, testing
order was randomized according to a Latin Squares design to prevent
an order effect and to cancel out the potential effect of fatigue.
Maximal oxygen consumption was defined as the highest VO2
obtained over any continuous 30-s time period, provided respiratory
exchange ratio (RER) was > 1.10. Maximal heart rate was defined
as the highest value recorded over any continuous 30-s period during
exercise. The protocols for both exercise modes were designed to
last approximately 8-12 min (Buchfuhrer et al., 1983).
After pre-screening and interviewing each subject, a specific elliptical
crosstrainer VO2max protocol (Figure
2) was selected based on gender and aerobic activity participation:
trained (aerobic exercise 3-5 hr/wk) and recreationally active (aerobic
exercise 2-3 hr/wk). After measuring resting expired gases for 5-min,
a 2-min warm-up was performed at a light workload prior to the start
of the exercise protocol. Figure
2 illustrates how the intensity for each elliptical crosstrainer
VO2max protocol was established and progressed throughout
VO2max testing by increasing either strides·min-1
and/or resistance·min-1. The incline (slope) remained
at level 6 during the entire test for all VO2max protocols.
A metronome was used to assure a consistent and correct strides?min-1
cadence. Incline was held constant at a setting of level 6 throughout
VO2max testing to eliminate any potential variability
in the calibration of the machine that the incline parameter would
have on physiological parameters. However, the calibration for the
resistance workload parameter is under the proprietary control of
the company and the assumption was made that this workload parameter
was accurate throughout VO2max testing protocols. The
criterion for termination of the exercise test was failure of the
participant to maintain within 20 strides·min-1 of target
cadence on the elliptical crosstrainer or volitional fatigue. Following
all maximal exercise tests (on both modes of exercise) each subject
exercised at a self-selected intensity until heart rate recovered
to less than 120 b·min-1.
On the treadmill, a modified Balke protocol was performed with subjects
selecting a comfortable running speed that could be maintained for
the duration of the test. After measuring resting expired gases
for 5-min, subjects were gradually brought to the selected running
speed for the first 2 min of the test, which was then maintained
throughout the duration of the test. The first 3 min of the protocol
was then performed at 0% grade, thereafter, each minute the treadmill
grade was increased by 1% until volitional fatigue was reached (Figure
data collection and analysis
A nose clip and three-way valve mouthpiece (Hans Rudolph Inc., Kansas
City, MO) were worn so that gas exchange data could be recorded
and analyzed. During the exercise test, VO2, VCO2,
VE, and respiratory
exchange ratio (RER) were measured breath-by-breath using a fast
response turbine flow transducer (K.L. Engineering Model S-430,
Van Nuys, CA) and custom developed software with AEI oxygen and
carbon dioxide electronic gas analyzers (AEI Technologies, Model
S-3A and Model CD-3H, Pittsburgh, PA). Raw signals were acquired
through a junction box via computer and integrated with a data acquisition
card (National Instruments, Austin, Texas). The turbine flow transducer
was calibrated prior to each testing session using a 3.0 L syringe.
Oxygen and carbon dioxide analyzers were also calibrated prior to
each testing session against known gas concentrations. All breath-by-breath
data were smoothed using a seven-breath moving average and averaged
into 30-s sampling intervals. Heart rate and electrocardiogram readings
were monitored continuously (Quinton 4000, Quinton, Seattle, WA)
using a 3-lead ECG configuration. Prior to the maximal exercise
tests, subjects rested for 5 min while resting gas exchange and
heart rate data were collected. The average values of heart rate
and VO2 recorded over the last 2 min of seated rest were
considered to be the resting values. For the subjects performing
both exercise modes, the two sets of resting data obtained were
pooled and averaged. Percentages of %HRR, %VO2R, and
%VO2max were calculated from the heart rate and VO2
values measured during the last 30 s of each stage.
All statistical procedures were completed using SPSS statistical
software (Version 13.0 SPSS for Windows, SPSS Inc., Chicago, IL).
The decision to use linear regression, rather than non-linear regression,
was based on the statistical analyses (linear regression) performed
by previous researchers to describe the %HRR vs. %VO2R
and %HRR vs. %VO2max relationships (Brawner et al., 2002;
Swain and Leutholtz, 1997;
Swain et al., 1998).
Prior to all data analyses, diagnostic tests were performed to check
for outlying or influential observations. The normality assumption
was checked using the Kolmogorov-Smirnov test and from visual inspection
of the normality plot. Two linear
regressions were performed for each individual subject: 1) the values
of %HRR vs. %VO2R, and 2) the values of %HRR vs. %VO2max.
For each individual trial, rest period, end-of-stage, and maximal
data were entered into the linear regression analysis. Mean (±SE)
values for intercepts, slopes, and Pearson r correlations were determined
for the two sets of regressions. Student t-tests (two-tailed) were
used to determine whether the mean group y-intercept and slope differed
from the line of identity (y-intercept = 0, slope = 1). To compare
the two exercise modes, student t-tests (two-tailed) were also used
to determine whether the slopes and intercepts were significantly
different between the two regressions. In addition, paired t-tests
(two-tailed) were used to determine whether there were significant
differences in the maximal physiological responses between the two
exercise modes. Finally, Pearson r correlations were used to determine
whether there were significant inverse relationships between VO2max
and %HRR vs. %VO2max y-intercept values for each of the
groups. The probability of making a Type I error was set at p <
0.05 for all statistical analyses. In the event of multiple analyses,
a Bonferroni adjustment of alpha level was performed.
Effect size and Power: The means and standard deviations of
previous studies (Brawner et al., 2002;
Swain and Leutholtz, 1997;
Swain et al., 1998)
were examined and the effect sizes of those studies were calculated.
Assuming that a power of 0.80 was needed and the calculated effect
sizes for %HRR vs. %VO2R and %HRR vs. %VO2max
were 0.8, it was determined that approximately 25 subjects would
be needed for each of the two exercise modality groups (Cohen, 1988).
physiological characteristics of the subjects are presented in Table
2. A comparison of mean VO2max, HRmax,
and RERmax values illustrated that there were no significantly
different physiological responses to maximal exercise testing between
the elliptical crosstrainer and treadmill exercise modes: VO2max,
t (23) = 0.431, p = 0.671; HRmax, t (23) = 1.328, p =
0.197; and RERmax, t (23) = -0.452, p = 0.656. Additionally,
there was no significant difference in mean protocol duration, t
(23) = -1.789, p = 0.087. Subjects required an average time of 11.3
min to complete the treadmill VO2max protocol versus
11.9 min to complete the elliptical crosstrainer VO2max
The regression results of %HRR vs. % VO2R and %HRR vs.
%VO2max for the ellipitcal crosstrainer group, elliptical
crosstrainer subgroup, and treadmill group are presented in Table
3. For all groups, both the y-intercept and slope for %HRR vs.
%VO2R fit the line of identity (y-intercept = 0, slope
= 1). Conversely, for all groups both the y-intercept and slope
of %HRR vs. %VO2max were significantly different (p <
0.001) from the line of identity (y-intercept ≠ 0, slope ≠
1). The regression lines are illustrated in Figure
In comparing the regressions of %HRR vs. %VO2R between
exercise modes (TM vs. ECT), there were no significant differences
(p > 0.05) for either y-intercept (ECT = 0.3 vs. TM = -0.3, t
(23) = 0.794, p = 0.435) or slope (ECT = 1.01 vs. TM = 1.00, t (23)
= -1.838, p = 0.079) values. Similarly, there were no significant
differences (p > 0.05) between exercise modes (TM vs. ECT) for
either y-intercept (ECT = -9.9 vs. TM = -10.0, t (23) = -0.151,
p = 0.881) or slope values (ECT = 1.12 vs. TM = 1.10, t (23) = -1.888,
p = 0.072) for the regressions of %HRR vs. %VO2max. The
regression lines for the comparison of %HRR vs. %VO2R
and %HRR vs. %VO2max between exercise modes are illustrated
in Figure 5.
Correlation analyses revealed significant inverse relationships
between VO2max and %HRR vs. %VO2max y-intercept
values for the entire elliptical crosstrainer group (r = 0.55, p
< 0.01) and subgroup (r = 0.53, p < 0.01); and the treadmill
group (r = 0.55, p < 0.01).
main finding of the present study is that %HRR is more closely aligned
with %VO2R, rather than %VO2max, during maximal
elliptical crosstrainer exercise. Similar results have been previously
reported for both treadmill and cycle exercise (Swain and Leutholtz,
Swain et al., 1998).
Swain and Leutholtz, 1997
found that during cycle exercise there is a significant discrepancy
in the line of identity between %HRR and %VO2max, that
was not evident between %HRR and %VO2R. Likewise, Swain
et al., 1998
and Brawner et al., 2002
determined that %HRR vs. %VO2R fit the line of identity
better than %HRR vs. %VO2max during treadmill exercise
in healthy and cardiac diseased populations, respectively. Our data
extend this principle to elliptical crosstrainer exercise, which
is a relatively new but common exercise mode.
The secondary purpose of the present study was to better understand
the influence of exercise mode on the relationship between %HRR
vs. %VO2R and %HRR vs. %VO2max during maximal
elliptical crosstrainer and treadmill exercise. Swain et al., 1998
suggested the reason that the regression of %HRR vs. %VO2R
fit the line of identity during cycle exercise, but was significantly
different during treadmill exercise, might be related to the mode
of exercise. However, these authors discounted a mode effect based
on earlier research findings from Davis and Convertino, 1975.
Findings from the current study are in agreement with this assessment.
Our data showed there are no significant differences in the regressions
of %HRR vs. %VO2R and %HRR vs. %VO2max between
elliptical crosstrainer and treadmill exercise. Additionally, there
were no significant differences in the line of identity (slope =
1, y-intercept = 0) for %HRR vs. %VO2R during treadmill
exercise. Swain et al., 1998
elevated temperatures might have been responsible for the significant
differences in the regression of %HRR vs. %VO2R during
treadmill exercise in their study. This interpretation may be likely
as our environmental conditions for temperature (21.4 oC)
were more similar to the cycle study (21.8 oC) by Swain
and Leutholtz, 1997
than the treadmill study (25.0 oC) by Swain et al., 1998.
Treadmill exercise is generally believed to elicit the highest VO2max
values in untrained and recreationally active individuals. Although
several studies, including the present investigation, demonstrated
similar VO2max values can also be obtained from other
modes of exercise. Haug et al., 1999
reported no significant differences in VO2max between
the treadmill (42.6 mL kg-1·min-1) and NordicTrack
cross-country ski simulator (42.5 mL·kg-1 min-1)
in both male and female subjects of varied fitness levels and cross-country
skiing experience. Likewise, similar VO2max values were
also reported between the treadmill (52.6 mL kg-1·min-1)
and VersaClimber (53.9 mL kg-1·min-1), a simulated
arm-leg climbing device, in collegiate varsity oarswomen and coxswain
(Brahler and Blank, 1995).
Our findings also showed comparable HRmax and RERmax
values between the treadmill and ellipitcal crosstrainer during
maximal exercise testing. While data collection in the present study
for the elliptical crosstrainer was conducted on the Precor EFX
546 Elliptical Fitness Crosstrainer, there are
other elliptical crosstrainer models being utilized in fitness settings
and rehabilitation facilities. As noted elsewhere (Haug et al.,
calibration between different models may vary considerably, limiting
application of the research findings that there are similar maximal
physiological responses between elliptical crosstrainer and treadmill
to the specific model used in the study.
In the present investigation, the %HRR vs. %VO2R and
%HRR vs. %VO2max relationships were described using linear
regression. However, the non-linear relationship between HR and
VO2 that has been described elsewhere in the literature
merits further discussion. The HR-VO2 relationship has
been depicted by several investigators (Bunc et al., 1995;
Hofmann et al., 1994;
Hofmann et al., 1997a)
as linear at lower-intensities, and then exhibiting a threshold
and change in slope at higher exercise intensities. Hofmann et al.
reported that only 6% of subjects demonstrated a linear HR response
during maximal exercise testing, compared to 94% that showed a non-linear
(downward or inverted deflection) HR response. Similarly, Vella
and Robergs, 2005
reported the HR-VO2 relation during incremental cycle
exercise in endurance-trained individuals was non-linear in the
majority (15 out of 18) of their subjects.
The consequences of assuming a linear relationship between HR and
VO2 throughout the intensity spectrum is the potential
for an over- or under-estimation of training workload. As noted
by Weltman et al., 1989,
depending on the nature of the HR-VO2 relation (downward
or inverted deflection), there may be considerable disparity in
the metabolic responses to exercise intensities of a given %HRR.
Visual examination of the %HRR vs. %VO2R and %HRR vs.
%VO2max (Figure 4)
data in the present study suggests the relationships can best be
described using linear regression. Similarly, the %HRR vs. %VO2R
and %HRR vs. %VO2max data illustrated in Figures 1
and 2 of Swain and Leutholtz,
also support the application of linear regression. Future research
is needed to determine whether the %HRR vs. %VO2R and
%HRR vs. %VO2max relationships could better be described
using non-linear regression.
As reported in previous research (Brawner et al., 2002;
Swain and Leutholtz, 1997;
Swain et al., 1998),
we found a significant inverse relationship between fitness level
and the disparity between %HRR vs. %VO2max for both exercise
modes. Lower fitness levels were associated with greater y-intercept
values for the entire elliptical crosstrainer group (r = 0.55) and
subgroup (r = 0.53), as well as the treadmill (r = 0.55). One of
the major advantages of prescribing exercise according to the relationship
between %HRR vs. %VO2R, rather than %HRR vs. %VO2max,
is that it results in a more accurate target heart rate throughout
the intensity spectrum (Swain et al., 1998).
This approach to the exercise prescription will minimize the % error
in exercise intensity, which is particularly important when working
with clientele that have low fitness levels.
If the assumption is made that %HRR is aligned with %VO2max
when establishing exercise training workloads, the magnitude of
error will be greatest at rest for low-fit clients and also throughout
the lower range of intensities. For example, an individual with
a VO2max of 17.5 mL kg-1·min-1,
will be at 20% (3.5 mL kg-1·min-1/17.5 mL
kg-1·min-1) of their VO2max at
rest, while an individual with a VO2max of 42 mL·kg-1
min-1, will be at 8.3% (3.5 mL·kg-1 min-1/42
mL kg-1·min-1) of their VO2max
at rest. Therefore, for the lower-fit individual there would be
an error of 20 units between %HRR and %VO2max at rest
compared to an error of 8.3 units for the higher-fit subject. The
magnitude of the error between %HRR and %VO2max would
lessen as exercise intensity is increased and both values reach
100%. However, as Swain and Leutholtz, 1997
have noted, a relatively small disparity between %HRR and %VO2max
can produce a substantial error in the prescribed exercise training
intensity. These errors can be avoided by prescribing training workloads
in terms of %HRR being equivalent to %VO2R, rather than
Another major advantage of prescribing exercise intensity based
on %VO2R, rather than %VO2max, is that it
provides an equivalent relative intensity for individuals of different
fitness levels. Consider the following example of two individuals
with VO2max values of 25 and 50 mL kg-1·min-1,
respectively. At rest, the 25 mL kg-1·min-1
individual is at 14% VO2max, while the 50 mL kg-1·min-1
individual is at 7% VO2max. If the intensity of the exercise
prescription is set at 50% VO2max, the 25 mL kg-1·min-1
individual increases by 36%, compared to the 50 mL kg-1·min-1
individual who increases by 43%, in terms of %VO2max.
The discrepancy in relative adjustments in training intensity in
the above example may result in disparate training effects between
the two individuals. Conversely, if the %VO2R method
were used, the individuals would both increase by identical adjustments
in relative intensity (Swain and Leutholtz, 1997).
on previous research findings, the American College of Sports Medicine
has changed its recommendations in recent editions; with exercise
prescription guidelines now reflecting that %HRR should be based
on %VO2R, not %VO2max (ACSM, 2006). Similar
findings in the current study are in agreement with this recommendation
and extend them to the elliptical crosstrainer, which is a relatively
new exercise modality. Additionally, it was found that the regressions
of %HRR vs. %VO2R and %HRR vs. %VO2max were
equivalent between the ellipitcal crosstrainer and treadmill. Future
studies are needed to confirm these findings among other exercise
modes, and in populations differing in age and health status.
study was funded by Precor, Inc.
The present study showed that %HRR is aligned with %VO2R, not
%VO2max, during maximal ellipitcal crosstrainer exercise.
was found that the relationships between %HRR vs. %VO2R and %HRR
vs. %VO2max were equivalent between the ellipitcal crosstrainer
study revealed that the elliptical crosstrainer produced similar
maximal physiological values (VO2max, HRmax, RERmax) compared
to treadmill running during VO2max testing.
Lance C. DALLECK
Employment: Ass. Prof. in the Department of Kinesiology,
University of Wisconsin at Eau Claire, Eau Claire, Wisconsin,
Research interests: Optimizing exercise programs for
health outcomes; quantifying energy expenditure during physical
activity and exercise; historical perspectives in exercise physiology.
Employment: Assoc. Prof. and Program Coordinator of Exercise
Science at the University of New Mexico, Albuquerque, New Mexico,
Research interests: Energy expenditure of physical activity;
exercise product testing and comparison.