Evaluation of ventilatory threshold and its relation to exercise habits among Japanese
Environ Health Prev Med
Evaluation of ventilatory threshold and its relation to exercise habits among Japanese
Nobuyuki Miyatake 0 1 2 3
Motohiko Miyachi 0 1 2 3
Izumi Tabata 0 1 2 3
Noriko Sakano 0 1 2 3
Takeshi Suzue 0 1 2 3
Tomohiro Hirao 0 1 2 3
Takeyuki Numata 0 1 2 3
0 T. Suzue T. Hirao Department of Public Health, Faculty of Medicine, Kagawa University , Miki-cho, Kita-gun, Kagawa 761-0793 , Japan
1 M. Miyachi I. Tabata National Institute of Health and Nutrition , Tokyo 162-8636 , Japan
2 N. Miyatake (&) N. Sakano Department of Hygiene, Faculty of Medicine, Kagawa University , Miki-cho, Kita-gun, Kagawa 761-0793 , Japan
3 T. Numata Okayama Southern Institute of Health , Okayama 700-0952 , Japan
Objective The aim of this study was to evaluate aerobic exercise levels, expressed in terms of ventilatory threshold (VT), in a Japanese population and explore the relationship between VT and exercise habits in this population. Methods This was a cross-sectional study in which data collected from 547 men and 524 women aged 20-69 years and not on medications, were used to assess exercise habits and parameters at VT, namely, oxygen uptake, work rate, and heart rate. Results Age-related changes in parameters at VT were noted. Of the participants, 205 men (37.5%) and 142 women (27.1%) had exercise habits. Oxygen uptake and work rate at VT in subjects with exercise habits were significantly higher than those without exercise habits after age had been adjusted for in both sexes. Anthropometric parameters were significantly correlated with oxygen uptake at VT, and the highest correlation coefficient rate
Exercise habits; Heart rate; Oxygen uptake; Ventilatory threshold; Work rate
-
was found between oxygen uptake at VT and body fat
percentage (men r = -0.589, women r = -0.631).
Conclusion The mean values determined here may
provide a useful database for evaluating VT in Japanese adult
subjects.
Introduction
Regular physical activity has been shown to increase the
level of high-density lipoprotein (HDL) in the blood and to
reduce resting blood pressure, abdominal fat, triglyceride
and fasting blood sugar levels, and insulin responses to the
oral glucose challenge test [
1–5
]. The National Nutrition
Survey in Japan [
6
] estimated that among the general
Japanese population, only 29.1% of men and 25.6% of
women exercised regularly (exercise habits). This report
also recommended that the proportion of the population
with exercise habits should be increased to 39% of men and
35% of women by 2010.
In 2006, the Japanese Ministry of Health, Labor and
Welfare-sponsored study Exercise and Physical Activity
Reference Quantity for Health Promotion 2006 (EPARQ
2006) recommended levels of maximal oxygen uptake as
reference quantities for exercise and physical activity
reference [
7
]. Although maximum oxygen uptake is
generally considered to be an accurate and reliable parameter, it is
not fully applicable to the general population in clinical
practice. Ventilatory threshold (VT) is defined as the
upper limit of aerobic exercise and is also thought to serve as
an accurate and reliable standard for exercise prescription
[
8
]. Since exercise intensity at VT is not harmful to
cardiovascular function, it can be safely applied to patients
with myocardial infarction as exercise prescription [
9
].
However, the link between VT and exercise habits in a large
sample of Japanese has not yet been investigated.
In the study reported here, we evaluated VT in Japanese
subjects and compared the results between subjects who
had exercise habits and those who did not.
Subjects and methods
Subjects
This was a cross-sectional study in which data on 547 men
(mean age 41.9 ± 10.9 years) and 524 women (mean age
44.5 ± 11.8 years) were evaluated. The age range of the
subject cohort was 20–69 years. The participants met the
following criteria (Table 1): (1) they had wanted to change
their lifestyle in terms of diet and exercise habits and had
undergone an annual health check-up at Okayama Southern
Institute of Health; (2) their VT and exercise habits had
been evaluated as part of their annual health check-up; (3)
they were not taking any medications. All subjects
provided written informed consent for the use of their data in
the study.
Ethical approval for the study was obtained from the
Ethical Committee of Okayama Health Foundation.
Anthropometric measurements
The anthropometric measurements included height, body
weight, abdominal circumference, hip circumference, and
body fat percentage. Height and body weight was measured
by AD-6225 (A&D Co, Tokyo, Japan). The body mass
index (BMI) was calculated using the formula weight/
(height)2 (kg/m2). Abdominal circumference was measured
at the umbilical level, and the hip circumference was
measured at the widest circumferences over the trochanter
in standing subjects after normal expiration [
10
]. Body fat
percentage was measured by an air displacement
plethysmograph called the BOD POD Body Composition System
(Life Measurement Instruments, Concord, CA) [
11, 12
].
The coefficient variation (CV, %) for same-day tests was
2.48, that for three separate-day tests was 2.27, and that for
independent operators was 4.53. There was a clear
correlation between the results from BOD POD and those from
dual-energy X-ray absorptiometry (DEXA) (r = 0.910,
P \ 0.01) [11].
Exercise testing
The subjects were asked to perform a graded ergometer
exercise procedure [
13
]. A resting electrocardiogram
(ECG) was recorded and the blood pressure was measured
in each subject 2 h after breakfast. Each participant then
began a graded exercise program after 3 min of pedaling
on an unloaded bicycle ergometer (Excalibur V2.0; Lode
BV, Groningen, the Netherlands). The profile of
incremental workloads was automatically defined by the
methods of Jones [
13
], in which the workloads reach the
predicted VO2max in 10 min. A pedaling cycle rate of
60 rpm was maintained. Loading was terminated when the
appearance of symptoms forced the subject to stop. During
the test, the ECG was monitored continuously together
with the recording of the heart rate (HR). Expired gas was
collected, and the rates of oxygen consumption (VO2) and
carbon dioxide production (VCO2) were measured
breathby-breath using a cardiopulmonary gas exchange system
(Oxycon Alpha; Mijnhardt, the Netherlands). The VT was
determined using the standard of Wasserman et al. [
8
],
Davis et al. [
14
], and the V-slope method of Beaver [
15
]
from VO2, VCO2, and minute ventilation (VE). Validation
and reproducibility of the VT were proven in a previous
study [
14
]. At VT, VO2 (ml/kg/min), work rate (W), and
HR (beats/min) were measured and recorded.
Exercise habits
Data on exercise habits were obtained at interviews
conducted by well-trained staff using the structured method of
the National Nutrition Survey in Japan. The subjects were
asked if they currently exercise (over 30 min per session,
two times per week for a duration of 3 months). When the
answer was ‘‘yes’’, they were classified as subjects with
exercise habits (exercised regularly). When the answer was
‘‘no’’, they were classified as subjects without exercise
habits.
Statistical analysis
Data were expressed as the mean ± standard deviation
(SD). Comparisons between two groups were performed
Women
Number
of subjects
Mean ± SD
Minimum
Maximum
Mean ± SD
Minimum
Maximum
using the unpaired t test and covariance analysis;
comparisons among more than three groups were performed by
the analysis of variance (ANOVA) and Scheffe’s F test.
P \ 0.05 was considered to indicate statistical significance.
The Pearson’s correlation coefficients were calculated to
test for the significance of the linear relationship among
continuous variables.
Results
Parameters at VT according to age group are summarized
in Table 2. In men, oxygen uptake and work rate at VT
decreased significantly with increasing age in subjects
[50 years and [40 years, respectively, and HR at VT
significantly decreased with increasing age in subjects [30
years. In women, oxygen uptake at VT decreased
significantly with increasing age in subjects [40 years, as did
both work rate and HR.
33.9
31.2
29.8
24.6
19.3
33.9
190.0
175.0
175.0
120.0
85.0
190.0
The prevalence of subjects with exercise habits is
summarized in Table 3. A total of 205 men (37.5%) and
142 women (27.1%) reported exercising regularly, and the
prevalence of subjects with exercise habits gradually
increased with age, being highest for subjects in their 60s
in both sexes (men 58.6%, women 55.4%).
We compared the VT in our subjects according to
Japanese subjects with and without regular exercise
habits (Table 4). The HR at VT in subjects with
exercise habits was similar to that in subjects without
exercise habits in men. Oxygen uptake and work rate at
VT in both sexes were significantly higher for subjects
with exercise habits than for those without exercise
habits. However, the age of subjects with exercise
habits was significantly higher than that of subjects
without exercise habits. Therefore, we used age as a
covariate and in a covariance analysis we compared VT
between our Japanese subjects with exercise habits and
those without. After adjusting for age in both sexes, we
found that oxygen uptake and work rate at VT were
significantly higher in subjects with exercise habits than
in those without.
We also compared VT between subjects with and
without exercise habits according to age group (Table 5).
Oxygen uptake at VT in men \50 years and in their 60s
and work rate at VT in men \50 years were significantly
higher in subjects with exercise habits than in those
without; in comparison, HR at VT in men in their 50s was
significantly lower in subjects with exercise habits than in
those without. In comparison, oxygen uptake at VT in
women \50 years and work rate at VT in women \60
years were significantly higher in subjects with exercise
habits than in those without.
Finally, we evaluated the relationship between oxygen
uptake at VT and age and anthropometric parameters
(Table 6; Fig. 1). Oxygen uptake at VT was negatively
correlated with age and anthropometric parameters. The
highest correlation coefficient was found between oxygen
P after adjusting
for age
In this study, we explored VT and its relation to exercise
habits in a Japanese population according to age groups.
This information should serve as a useful database for
evaluating VT in Japanese subjects.
The prevalence of subjects with exercise habits in Japan
was reported to be 29.1% of men and 25.6% of women by
the National Nutrition Survey in Japan. The definition of
duration in our study, namely, 3 months, was shorter than
that in the survey definition, and we did not enroll subjects
who took medications. The subjects participating in our
study undertook annual health check-ups and exercise tests
and, consequently, they may be more careful of their
own health than the subjects in the National Nutrition
Survey. Therefore, our results according to the analysis of
subjects without medications were higher than those in the
Survey.
There are only a few reports on maximal oxygen uptake as
a direct measure in healthy Japanese individuals. Ohta et al.
[
16
] reported that maximal oxygen uptake significantly
decreased with age in 832 apparently healthy subjects and
could be expressed as a single regression formula: y
(maximal oxygen uptake in ml/kg/min) = 46.6 - 0.36 9 age
(r = -0.447) in men and y = 35.3 - 0.23 9 age (r =
-0.407) in women. We also found an age-related decrease in
maximal oxygen uptake among Japanese not taking
medications, as reported earlier [
17
]. It has also been reported that
there is significant loss in oxygen uptake at VT with aging
[
18, 19
]. Sanada et al. [18] reported a negative correlation
between oxygen uptake at VT and age in 1463 Japanese.
Miura reported that oxygen uptake at VT was significantly
correlated with age (men r = -0.626, women r = -0.578)
in 610 Japanese [
19
]. In this latter study, an age-related
Age
Men
decrease of VT was noted among Japanese not taking
medications. These mean values hold promise as a quite useful
database for evaluating VT in Japanese subjects.
Although oxygen uptake and work rate at VT in subjects
with exercise habits was significantly higher than those in
subjects without exercise habits after age had been adjusted
for, we found no significant differences in oxygen uptake at
VT for men in their 50s and women [50 years nor in work
rate at VT in men [50 years and women [60 years.
According to the National Nutrition Survey in Japan, the
prevalence of subjects with exercise habits increases with
age, while daily step counts decrease with age [
20
]. Lower
exercise intensity and shorter exercise time in elderly
adults as well as the small sample size may make it difficult
to infer causality between VT and exercise habits in these
groups. Based on their analysis of 709 apparently healthy
Japanese men and women, Zhang et al. [
21
] also showed
that, relative to the subgroup with the fewest walk steps, a
significantly greater peak oxygen uptake occurred only in
females aged 30–49 years. However, Sandvik et al. [
22
]
reported that physical fitness was a graded, independent,
long-term predictor of mortality from cardiovascular
causes in healthy, middle-aged men. Miura [
19
] have that
oxygen uptake at VT was positively correlated with mean
number of steps per day. Jones et al. [
13
] also reported that
the extent of leisure time activity exerted a positive
influence on VO2. Therefore, it seems reasonable to suggest
that mortality among a proportion of the Japanese
population may possibly be decreased simply by improving
oxygen uptake at VT through the promotion of exercise
habits.
A relationship between maximal oxygen uptake and
body composition has been reported in the literature.
Significant relationships between maximal oxygen uptake and
body fat percentage were noted in Japanese junior high
school boys and girls [
23
], African-American adolescents
[
24
] and Danish women [
25
]. In an earlier study, we also
found that maximal oxygen uptake was significantly
correlated with body fat percentage as measured by dual X-ray
absorptiometry [
17
]. Although we could not infer causality
between oxygen uptake at VT and body fat percentage and
we could not directly measure visceral fat area by
computed tomography in this study, an excess of body fat,
which is expressed as body fat percentage (%), may be an
excess weight and play a critical role in determining
oxygen uptake at VT. This result suggests that body fat
percentage may be a good predictor for estimating oxygen
uptake at VT in Japanese.
In conclusion, the mean values reported here may
provide a useful database for evaluating VT in Japanese adult
subjects. Although oxygen uptake and work rate at VT in
subjects with exercise habits were significantly higher than
those in subjects without exercise habits after age had been
adjusted for, there were no significant differences in
oxygen uptake at VT in men in their 50s and in women [50
years. In addition, this study was a cross-sectional—not a
longitudinal—study. Further prospective investigation
studies to evaluate the relationship between VT and
exercise habits should be carried out in the general Japanese
population.
Acknowledgments This research was supported in part by Research
Grants from the Ministry of Health, Labor, and Welfare, Japan.
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