Download The efficacy of accumulated short bouts versus

HEALTH EDUCATION RESEARCH
Theory & Practice
Vol.14 no.6 1999
Pages 803–815
The efficacy of accumulated short bouts versus single
daily bouts of brisk walking in improving aerobic
fitness and blood lipid profiles
K. Woolf-May, E. M. Kearney1, A. Owen3, D. W. Jones2, R. C. R. Davison
and S. R. Bird
Abstract
Fifty-six subjects (19 men and 37 woman) aged
between 40 and 66 completed the study. They
were allocated into three walking groups and a
control group (C). The three walking groups
performed the same total amount of walking
for 18 weeks, but completed it in bouts of
differing durations and frequencies. These were
Long Walkers (LW; 20–40 min/bout), Intermediate Walkers (IW; 10–15 min/bout) and
Short Walkers (SW; 5–10 min/bout); with the
IW and SW performing more than one bout of
walking a day. Following the 18 week walking
programme, compared to the C group all walking groups showed similar improvements in
fitness as determined by a reduction in blood
lactate during a graded treadmill walking test
(LW 1.0 mmol/l; IW 0.8 mmol/l; SW 1.2 mmol/l;
C 0.2 mmol/l; P ⍧ 0.003) and reduction in final
heart rate (LW 8 beats/min; IW 6 beats/min;
SW 10 beats/min; C 0 beats/min; P ⍧ 0.056).
Also compared to the C group, the LW and
IW groups recorded statistically significant
decreases in low-density lipoprotein cholesterol
(LW 0.29 mmol/l; IW 0.41 mmol/l; P ⍧ 0.024),
whereas the control group showed a mean
increase of 0.22 mmol/l. The LW and IW groups
also showed significant reductions in apolipo-
Department of Sport and Exercise Science, Canterbury
Christ Church University College, Canterbury CT1 1QU,
1Department of Pathology, Queen Elizabeth the Queen
Mother Hospital, Margate CT9 4AN, and 2Haemophilia
Centre and 3Department of Cardiology, Kent and
Canterbury Hospital, Canterbury CT1 3NG, UK
© Oxford University Press 1999
protein (apo) A-II (LW 0.05 g/l; IW 0.02 g/l;
SW 0.01 g/l; C 0.00 g/l; P ⍧ 0.012) with the
LW recording a statistically significant increase
in the ratio of apo A-I/A-II (LW, 0.19, P ⍧
0.044). In conclusion, some health benefits were
achieved from all walking programmes. However, whilst the changes in aerobic fitness were
similar, the effects upon blood lipid profiles were
not. The findings from this study suggest that
the LW regimen was most effective in benefiting
blood lipid profile, followed by the IW regimen,
with the SW being least potent. Nevertheless,
for the sedentary/low-active members of society,
any improvement in health may be considered
as important. Therefore accumulated bouts of
moderate intensity exercise, which according to
theories of exercise behaviour may be more
easily incorporated into an individual’s lifestyle
than single prolonged bouts, may be advocated
for health promotion but may not be as effective
as the traditionally prescribed 20–40 min bouts.
Introduction
An active lifestyle which includes regular exercise
is reported to promote physical capacity, quality
of life and self-esteem, as well as reducing the risk
of certain diseases (Bouchard et al., 1994, Morris
1994). In this area, the effects of aerobic exercise
have received particular attention because of its
link with a reduced risk of cardiovascular disease.
This may be via both a direct independent
effect (Paffenbarger et al., 1986, Sharper and
Wannamethee, 1991; Farrell et al., 1998) and via
its influence upon other established risk factors
(Blair et al., 1995).
803
K. Woolf-May et al.
Evidence for the benefits of regular aerobic
activity include its effects in producing increased
concentrations of total apolipoprotein (apo) A
(Rauramaa et al., 1995), apo A-I and A-II
(Thompson et al., 1988), high-density lipoprotein
cholesterol (HDL-C) (Ebisu, 1985; Thompson
et al., 1988; Suter et al., 1990; Seip et al., 1993),
subfraction HDL2 (Ballantyne et al., 1982; Wood
et al., 1983), and the proportion of HDL-C/lowdensity lipoprotein cholesterol (LDL-C) (Seip
et al., 1993). In addition, exercise has also been
shown to decrease total cholesterol (TC), triacylglycerol (TAG), very-low-density lipoprotein
(VLDL) and apo B (Tamai et al., 1992; Seip et al.,
1993). The implications of these changes have
been linked to the prevention or slowing down of
the atherosclerotic process (Kramsch et al., 1981)
and consequently have clear benefits to an individual’s cardiovascular health.
It is therefore unfortunate that even though the
benefits of regular exercise have been widely
publicized, the findings from the Allied Dunbar
National Fitness Survey in the UK (Allied Dunbar
National Fitness Survey, 1990) and a relatively
recent investigation carried out by Caspensen and
Merritt in the US (Caspensen and Merritt, 1995)
indicate that the large majority of these populations
do not reach the activity levels recommended for
good health. From this and other studies it is
apparent that whilst most individuals believe
exercise to be beneficial to their health, few are
succeeding in incorporating the traditionally prescribed 20–30 min of vigorous exercise, 3–5 times
a week into their lifestyle. Reasons for this emerged
from the study conducted by Killoran (Killoran,
1994) in which the most common reasons given
for not participating in physical activity were ‘I
haven’t got the time’ (41% of men and 44% of
women) and ‘I am not the sporty type’ (24% of
men and 37% of women). Therefore to overcome
these barriers the health promoter must convey to
the general population that a physically active
lifestyle is not synonymous with sport and that
appropriate forms of exercise can be included
within an individual’s daily routine without placing
greater demands upon their time (Hillsdon et al.,
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1995). Furthermore it is apparent that the formation
of exercise habits is an essential aspect of exercise
participation and adherence (Aarts et al., 1997).
Consequently, completing short walks, such as
from the home to the station, the station to the
office and back again would seems to be an
eminently suitable activity, but has yet to be proven
to be as effective as the traditionally prescribed
20–30 min sustained bout of moderately
vigorous exercise.
In 1995 the Centre for Disease Control and
Prevention and American College of Sports Medicine published a statement suggesting that health
benefits may be accrued from accumulating 30
min of moderate intensity exercise during a day
(Pate et al., 1995). However, to date research
evidence on the effects of accumulated short bouts
of activity is limited and the findings are sometimes
inconsistent. For example, some of the research
on the effects upon aerobic fitness report that
exercise regimens consisting of repetitive short
bouts are less effective than single prolonged bouts
at improving the aerobic fitness of those who
previously did not exercise on a regular basis
(Jakicic et al., 1995; Synder et al., 1996) or who
previously exercised for less than 60 min/week
(DeBusk et al., 1990). Conversely, others have
found little difference in the effectiveness of continuous and accumulative bouts with untrained
males (Ebisu 1985) and individuals whose habitual
exercise was less than 60 min/week (Woolf-May
et al., 1998).
Similarly research into the effects of accumulated exercise upon blood lipids has also been
equivocal. Ebisu (Ebisu, 1985) reported that
accumulative bouts of daily exercise could be more
effective in enhancing blood lipid profile than a
single daily bout amongst a group of previously
untrained 21 year olds, whereas others have found
neither accumulative nor single bouts of daily
exercise to produce any change in blood lipid
profile (Woolf-May et al., 1998). Therefore, the
aim of this study was to further investigate the
effects of single and accumulated short bouts of
walking upon aerobic capacity and blood lipid
profile.
Brisk walking to improve aerobic fitness
Methods
Subject details and selection
Volunteers were recruited through an editorial in
the local newspapers and a radio feature, which
asked for sedentary but otherwise healthy individuals over the age of 40 years. Following written
consent from the participants, medical screening
and an activity questionnaire, volunteers were
excluded from the study if they had high resting
blood pressure of either greater than 160 mmHg
systolic and/or 95 mmHg diastolic, or a previous
history of cardiovascular disease, or a lifestyle
which included more than 60 min/week of moderate intensity activity which made them slightly
breathless or sweaty, including walking. This was
followed by a ‘permission to participate’ form
which was completed by the volunteer’s GP. Once
cleared to participate, 79 subjects (25 men and 54
woman) aged between 40 and 66 years were
deemed suitable for the study. Subjects were
allocated into four groups: long walking group
(LW), intermediate walking group (IW), short
walking group (SW) and controls (C), using a
stratified random allocation to produce groups
which were similar in age and gender. Analysis
of variance indicated no significant difference
between the groups (P ⬎ 0.1) for age, height and
body mass, both for the initial subject cohort of
79 subjects and the pre-intervention values for the
56 who completed the study (Table I). All analysis
and data presented in this paper is based upon the
56 subjects who completed the study; with the
exact subject numbers varying between factors as
some subjects were unable to provide sufficient
blood for analysis and/or complete the second
fitness test.
Graded treadmill walking test (GTWT)
for the assessment of aerobic fitness
Prior to commencing the walking intervention,
all subjects reported to the Exercise Physiology
Laboratory at Canterbury Christ Church College
for a GTWT. Before each test the subject’s height
(only taken pre-intervention) and body mass were
determined using a stadiometer and clinical scales
(052466; Seca, Germany) with the subjects wearing
similar minimal clothing pre- and post-intervention.
The test was conducted on a motorized treadmill
(XELG70; Woodway, Weil am Rhein, Germany)
that had been calibrated using a clinometer
(Trumeter; Survey Supplies, Hounslow, UK). Subjects walked at 4.8 km/h throughout the test which
commenced at a gradient of 0% if subjects were
aged over 50 years and 2.5% if aged below 50
years. The protocol was continuous and the gradient
increased by 2.5% every 4 min. Subjects were
asked to complete four stages but the test would
be terminated before the end of the fourth stage if
the subject’s heart rate rose to within 10 beats/min
of their age-predicted HR max (Londeree and
Moeschberger, 1982) and/or they showed signs of
distress, or if the subject felt they no longer wanted
to proceed. Heart rate was monitored using short
wave telemetry (Sportstester; Polar Electro,
Kempele, Finland). Expired air was collected via
a Hans Rudolf breathing mask with 2730 series
large Y-shaped valves (Hans Rudolf, Kansas City,
KS) and low resistance ducting. Oxygen consumption was assessed using an on-line Covox Microlab
analyser (Fitness Research Systems, Exeter, UK).
Each subject’s V̇O2 max was estimated by the extrapolation of heart rate and oxygen consumption
to their predicted maximum heart rate, 210 –
(age⫻0.65) (Maritz et al., 1961). During the last
minute of each stage a capillary blood sample was
collected from a fingertip using an autolet lancet
(Owen Mumford, Woodstock, UK). This was
immediately analysed using a YSI 2300 stat plus
(Yellow Springs Instrument, Yellow Springs, OH;
CV 2.3% within batch and ⬍0.1 mmol/l between
batches). A further use of the GTWT was to
correlate the subject’s oxygen consumption and
heart rate whilst walking. This enabled an estimation of their energy expenditure at particular
heart rates.
Collection and analysis of venous blood
samples
Venous blood samples were taken from the subjects
pre- and post-exercise intervention. Samples were
805
K. Woolf-May et al.
Table I. Subject characteristics pre-intervention for those that completed the study, including post-intervention body mass
(mean ⫾ SD)
n
LW
males
females
combined
IW
males
females
combined
SW
males
females
combined
Controls
males
females
combined
Age
Height (m)
Mass pre-intervention
(kg)
Predicted V̇O2 max
(ml/kg/min)
Predicted V̇O2 max
(l/min)
Years
Range
6
13
19
53.3 (8.6)
49.9 (4.9)
50.1 (6.3)
43–65
41–57
41–65
1.78 (0.07)
1.66 (0.07)
1.70 (0.09)
83.7 (6.6)
75.5 (13.7)
78.1 (12.4)
33.9 (6.2)
26.1 (5.0)
27.8 (6.5)
2.7 (0.7)a
2.1 (0.4)b
2.2 (0.6)c
3
7
10
55.7 (7.8)
58.6 (5.7)
57.7 (6.1)
47–65
48–66
47–66
1.72 (0.04)
1.64 (0.07)
1.66 (0.07)
73.8 (8.6)
68.8 (7.0)
70.3 (7.4)
29.3 (3.9)
24.9 (5.4)
25.7 (7.3)
2.2 (0.4)
1.7 (0.5)
1.8 (0.5)
5
9
14
54.2 (3.7)
53.6 7.3)
54.3 (7.4)
45–65
41–64
41–65
1.75 (0.05)
1.61 (0.06)
1.66 (0.09)
87.8 (17.4)
66.3 (9.5)
74.0 (16.9)
31.3 (7.2)
22.6 (6.6)
27.3 (6.8)
2.7 (0.7)d
1.6 (0.5)
1.9 (0.7)b
5
8
13
58.2 (3.7)
52.5 (7.9)
54.7 (7.0)
53–62
40–66
40–66
1.70 (0.06)
1.65 (0.06)
1.67 (0.06)
75.6 (5.9)
67.3 (7.1)
70.5 (7.7)
34.7 (11.6)
27.0 (7.0)
30.4 (9.3)
2.8 (0.9)
1.6 (0.3)
2.1 (0.8)
⫽ 17; bn ⫽ 12; an ⫽ 5; dn ⫽ 3.
There were no statistically significant differences (P ⬎ 0.08) between the LW versus IW versus SW versus C for age, height,
body mass or V̇O2 max (l/min) or V̇O2 max (ml/kg/min) (P ⬎ 0.783 males, P ⬎ 0.379 females and P ⬎ 0.530 combined data).
There were no statistically significant differences between the LW versus IW versus SW versus C (P ⬎ 0.1) in the amount of
change in body mass (kg) post-intervention.
cn
collected at the Phlebotomy Department of the
Kent and Canterbury Hospital, following an overnight fast. Post-intervention samples were taken at
least 24 h after the subjects’ last walking bout.
Samples for TAG, TC and HDL-C were analysed
immediately after collection. Aliquots of serum for
apo were frozen at –70°C before analysis of the
pre- and post-samples in a single batch by the
Biochemistry Department of the Kent and
Canterbury Hospital who were blinded to the group
allocation of the subjects. When providing their
pre-intervention sample all pre-menopausal
females were asked to complete a form indicating
the stage of their menstrual cycle. This enabled
the researchers to arrange for their post-intervention blood samples to be collected at the same
stage, thereby limiting the potential effects of this
factor on the results.
All blood samples were analysed for plasma
concentrations of TC (CV 1.4–4.1% between
batches), TAG (CV 1.6–1.8% between batch) and
806
HDL-C (CV 3.7–4.4% between batch) using a
Vitors Analyser 700XRC with FDA approved kits
(Ortho-Clinical Diagnostics, Amersham, UK).
LDL-C was calculated using the Friedwald formula. Apo A-I (CV 5% within batch) and B
(CV 5% within batch) were assayed using rate
nephlometry using the Beckman array (Beckman
Instruments, High Wycombe, UK). Apo A-II was
assayed by immunoturbidimetry (CV 1.1% within
batch and 1.9% between batches) on a Cobas
MIRA (Roche, Welwyn Garden City, UK) using
the Immuno kit (Immuno, Sevenoaks, UK). Ratios
of A-I/B, A-I/A-II, TC/HDL-C and LDL-C/HDL-C
were also determined.
Exercise intervention programmes
Subjects allocated to the exercise groups embarked
upon an 18 week walking programme which
incorporated a gradual increase in activity. The
programmes commenced with a total of 60 min
walking in the first week, increasing to 200 min
Brisk walking to improve aerobic fitness
by the ninth week of the study. The prescribed
exercise intensity was determined to be approximately 70–75% of each individual’s predicted
V̇O2 max . The prescribed exercise programmes
aimed to produce an energy expenditure of about
4.2 MJ/week over the last 10 weeks of the programme. This was based upon the work of Superko
(Superko, 1991) who when reviewing the subject
suggested it to be effective in producing healthrelated adaptations in blood lipid profiles. Energy
expenditure was estimated individually from each
subject’s first GTWT. This was based upon the
work of Durnin and Passmore (Durnin and
Passmore, 1967) from which it was estimated
that each litre per minute of oxygen consumed
corresponded to an energy expenditure of 0.02 MJ/
min (5 kcal/min). Establishing individual heart
rate and energy expenditure regression equations
enabled an estimation of each subject’s energy
expenditure to be determined from the heart rate
and walking duration data recorded in their training diaries.
Members of the LW group were requested to
walk no less than 20 min and no more than 40
min once a day. Subjects in the IW group were
instructed to walk for no less than 10 min and no
more than 15 min in each exercise bout, and not
to complete more than three bouts of walking per
day, with no less than 120 min between each bout.
The SW group were instructed to walk no less
than 5 and no more than 10 min in each walking
bout, completing no more than four bouts per day,
with no less than 120 min between each bout.
In order to monitor and assist with the determination of exercise intensity whilst walking, 20 of
the subjects were allocated heart rate monitors
(Sportstester; Polar Electro, Kempele, Finland).
They were also instructed to take their heart rate
manually from their pulse palpated at the wrist
and a regression equation was established between
the two (HR telemetry ⫽ 88.1 ⫹ 0.347 HR
palpated, P ⬍ 0.0001). This gave a better indication
of the actual exercise heart rate of those not
issued with heart rate monitors. To document their
activities, all walking subjects were given a training
diary, in which they were instructed to record the
duration and intensity of all walking bouts.
Subjects completed their walking bouts in a way
which fitted into their lifestyle. In order to aid
compliance to the walking programmes, all walking
subjects were offered optional once-weekly supervised walking sessions at the College. Additionally,
all subjects were sent a newsletter at the midway
stage of the walking programme to help maintain
their motivation and a further letter 3 weeks
before completion. These were supplemented by
individual phone calls and subjects were provided
with a contact number to call if they needed help
or information. Subjects in group C were asked to
maintain their current lifestyle for the duration of
the study. All subjects were asked not to make any
changes to their regular diet.
Statistical analysis
The Minitab statistical package was employed for
the statistical analysis of the results, using the 0.05
level as indicating a statistical difference. A oneway analysis of variance (ANOVA) was used to
assess baseline pre-intervention differences
between the groups and a post hoc Scheffe test
applied when required. For non-parametric data a
Kruskal–Wallis test was used. To determine any
post-intervention changes, analysis of covariance
(ANCOVA) was employed using the method
described by Oldham (Oldham, 1968). The general
linear model (GLM) was used for non-parametric
data. In order to identify the origin of statistical
differences the one-way ANOVA and post hoc
Scheffe test were utilised as a post hoc test for the
ANCOVA analysis (parametric data only).
Results
Walking programmes (Table II)
During the study the groups walked with an average
heart rate of: LW 130 ⫾ 9 beats/min (73.4 ⫾ 4.8%
HR max), IW 129 ⫾ 7 beats/min (74.8 ⫾ 3.8%
HR max) and SW 130 ⫾ 8 beats/min (74.6 ⫾
4.1% HR max). Analysis of the data indicated that
over the entire duration of the study the groups
walked an average of; LW 158 ⫾ 10 min/week;
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K. Woolf-May et al.
Table II. Descriptive data from the training diaries (mean ⫾ SD) [LW (n ⫽ 19), IW (n ⫽ 10) and SW (n ⫽ 14)]
LW
IW
SW
18.3 (0.8)
18.0 (0.7)
18.4 (0.7)
2871.2 (298)
2661.7 (276)
2855.0 (394)
Minutes per week walked for whole programme
157.8 (10.1)
148.8 (15.0)
154.6 (23.3)
Total estimated gross energy expenditure from walking (MJ)
77.8 (24.2)
~18537 (5770) kcal
66.8 (30.1)
~15910 (7155) kcal
73.6 (37.0)
~17521 (8819) kcal
No. of weeks walked
Total minutes walked
Gross estimated additional energy expenditure from walking throughout the programme (MJ/week)
4.3 (1.3)
3.8 (1.7)
~1017.3 (303) kcal
~892 (401) kcal
4.0 (2.0)
~955 (479) kcal
Gross estimated additional energy expenditure from walking for final 10 weeks of programme (MJ/week)
5.0 (1.7)
4.2 (1.6)
~1200 (410) kcal
~1000 (390) kcal
4.5 (1.9)
~1070 (450) kcal
Estimated percentage of age predicted heart rate whilst walking (beats/min)
73.4 (4.8)
74.8 (3.8)
74.6 (4.1)
Estimated percentage of V̇O2 max whilst walking (ml/kg/min)
67.4 (4.0)
67.1 (3.9)
67.4(3.3)
14.5 (0.8)a
9.9 (0.3)a
14.6 (0.4)a
10.2 (0.6)a
10.6 (1.2)a
15.4 (1.1)a
5.8 (2.2)
4.8 (1.1)
Duration of each walking bout (min)
34.8 (1.0)a
Duration of each walking bout during the last 10 weeks (min)
39.4 (1.6)a
No. of walking bouts per week
4.4 (0.3)a
Duration between each walking bout (h)
aAll
groups statistically significantly different from each other (P ⬍ 0.0001).
IW 149 ⫾ 15 min/week and SW 155 ⫾ 23 min/
week. During the final 10 weeks of the study the
average duration of walking for the groups were:
LW 185 ⫾ 21 min/week, IW 169 ⫾ 26 min/week
and SW 178 ⫾ 23 min/week. This corresponded
to a gross estimated 18 week average energy
expenditure from the walking of: LW 4.3 ⫾ 1.3 MJ/
week, IW 3.8 ⫾ 1.7 MJ/week and SW 4.0 ⫾
2.0 MJ/week. During the final 10 weeks of walking
this corresponded to a mean estimated energy
expenditure from walking of: LW 5.0 ⫾ 1.7 MJ/
808
week, IW 4.2 ⫾ 1.6 MJ/week and SW 4.5 ⫾
1.9 MJ/week.
Statistical analysis revealed significant differences (P ⬍ 0.0001) between all groups (LW versus
IW versus SW) in the mean amount of minutes
walked in each exercise bout, mean amount of
minutes walked in each exercise bout during the
last 10 weeks and mean number of walking bouts
per week. There were no statistically significant
differences (P ⬎ 0.1) between the IW and SW in
mean amount of hours between each walking bout
Brisk walking to improve aerobic fitness
Table III. GTWT heart rate (for final test stage), predicted V̇O2 max and blood lactate data (for final test stage), pre- and postintervention (mean ⫾ SD) for LW, IW, SW and C (ANCOVA statistical analysis of differences between pre- and post-intervention
values)
Heart rate (beats/min)
LW
IW
SW
C
n
Pre-intervention
Post-intervention
Mean difference
P
17
8
12
13
144
137
143
142
136
131
133
142
–8
–6
–10
0
0.056
Predicted V̇O2 max (ml/kg/min)
LW
17
IW
10
SW
12
C
10
Blood lactate (mmol/l)
LW
IW
SW
C
6
5
8
10
(14.4)
(10.7)
(14.0)
(20.5)
(15.0)
(14.3)
(11.7)
(15.6)
27.8
25.7
27.0
30.4
(6.4)
(7.3)
(6.8)
(9.3)
31.6
29.3
30.6
29.2
(6.6)
(10.0)
(6.7)
(9.2)
3.8
4.2
3.6
–1.2
0.299
2.2
2.4
2.6
2.5
(0.3)
(0.5)
(1.2)
(1.1)
1.2
1.6
1.4
2.3
(0.5)
(0.4)
(0.9)
(0.7)
–1.0a
–0.8
–1.2a
–0.2
0.003
aStatistically
significantly different (P⫽0.003) amount of change from the controls for the LW and SW as determined by oneway ANOVA and post hoc Scheffe test.
or for any of the other measured variables. There
were no statistically significant differences between
any of the groups in total estimated energy expenditure from walking over the 18 weeks (LW versus
IW versus SW P ⬎ 0.6), estimated mean weekly
energy expenditure from walking (LW versus IW
versus SW P ⬎ 0.7) or estimated mean weekly
energy expenditure from walking over the last 10
weeks of the programme (LW versus IW versus
SW P ⬎ 0.1).
Aerobic fitness, GTWT (Table III)
All subjects bar one completed the required four
stages of the GTWT. Pre-intervention there were
no significant (P ⬎ 0.4) differences in any of the
measured variables, indicating all groups were
similar in these factors.
Post-intervention, when compared to the control
group C, blood lactate concentration was reduced
in all walking groups in the final stage of the
test (P ⬍ 0.005). Differences in pre- and postintervention heart rate during the final stage of the
test bordered upon statistical significance (P ⫽
0.056), being reduced in all walking groups but
no change in the C group.
Blood lipid, lipoprotein and apo data
(Tables IV and V)
Due to the possibility that there could be male/
female differences in ‘blood profile’, an analysis
was undertaken to determine if there were any
gender differences.
Males and females did not differ statistically in
baseline values for, TC TAG, LDL-C, apo A-I,
apo A-II or apo B or for ratios of A-I/B and A-I/
A-II (Table IV). Therefore, analysis of these factors
were not separated into gender sub-groups. However, for those factors that did differ between the
genders (HDL-C, P ⬍ 0.0001, and ratios TC/
HDL-C, P ⬍ 0.02 and LDL-C/HDL-C, P ⬍ 0.02)
separate analysis between the subjects groups was
carried out (LWmale versus IWmale versus SWmale
versus Cmale and LWfemale versus IWfemale versus
SWfemale versus Cfemale) (Table V). The male subgroups showed no significant difference between
baseline pre-intervention values (LWmale versus
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K. Woolf-May et al.
Table IV. Combined male and female data for serum concentration of Apo and selected ratios and plasma concentrations of
lipids and lipoproteins (mean ⫾ SD) (ANCOVA statistical analysis of differences between pre- and post-intervention values for
the LW, IW, SW and C groups)
n
Pre-intervention
Post-intervention
Mean difference
P
Apo A-I (g/l)
LW
IW
SW
C
18
10
13
11
1.39 (0.37)
1.43 (0.42)
1.49 (0.23)
1.49 (0.15)
1.32
1.41
1.50
1.43
(0.34)
(0.12)
(0.24)
(0.14)
–0.07
–0.02
0.01
–0.06
0.226
Apo A-II (g/l)
LW
IW
SW
C
18
10
13
11
0.46
0.45
0.40
0.39
0.41
0.43
0.41
0.39
(0.08)
(0.08)
(0.09)
(0.06)
–0.05c
–0.02c
–0.01
0.00
0.012
Apo B (g/l)
LW
IW
SW
C
18
10
13
11
1.10 (0.34)
1.10 (0.16)
1.00 (0.31)
1.10 (0.24)
1.02 (0.32)
1.00 (0.17)
0.92 (0.35)
1.11 (0.29)
–0.08
–0.10
–0.08
0.01
0.263
Apo A-I/B
LW
IW
SW
C
18
10
13
11
1.34 (0.52)
1.32 (0.21)
1.64 (0.64)
1.41 (0.34)
1.39
1.44
1.94
1.39
(0.54)
(0.24)
(0.93)
(0.45)
0.05
0.12
0.30
–0.02
0.517
Apo A-I/A-II
LW
IW
SW
C
18
10
13
11
3.05
3.26
3.73
3.93
(0.75)
(0.46)
(0.67)
(0.49)
3.24
3.39
3.75
3.77
(0.91)
(0.56)
(0.86)
(0.52)
0.19b
0.13
0.02
–0.16
0.044
TC (mmol/l)
LW
IW
SW
C
18
10
12
12
5.80
5.86
5.90
5.83
(1.30)
(0.60)
(1.10)
(0.93)
5.57
5.55
5.86
5.92
(1.22)
(0.74)
(1.26)
(0.95)
–0.23
–0.31
–0.04
0.06
0.199
TAG (mmol/l) (CDC traceable standard)
LW
18
1.42 (0.71)
IW
10
1.10 (0.50)
SW
12
1.20 (0.44)
C
12
1.31 (0.65)
1.40
1.00
1.21
1.60
(0.72)
(0.38)
(0.48)
(0.84)
–0.02
–0.10
0.01
0.29
0.060
LDL-C (mmol/l)
LW
IW
SW
C
4.66
4.53
4.80
5.20
(1.52)
(0.83)
(1.44)
(1.46)
–0.29a
–0.41a
–0.13
0.22
0.024
18
10
12
12
4.95
4.94
4.93
4.98
(0.08)
(0.08)
(0.06)
(0.06)
(1.54)
(0.68)
(1.26)
(1.28)
significantly different (P ⬍ 0.03) amount of change compared to controls as determined by one-way ANOVA and
post hoc Scheffe test.
bStatistically significantly different (P ⬍ 0.05) amount of change compare to controls as determined by one-way ANOVA and
post hoc Scheffe test.
cStatistically significantly different (P ⬍ 0.02) amount of change compared to controls as determined by one-way ANOVA and
post hoc Scheffe test.
aStatistically
810
Brisk walking to improve aerobic fitness
Table V. Separate male and female data for plasma concentrations of HDL-C and serum concentrations of apo A-I, and ratios
of TC/HDL-C and LDL-C/HDL-C (mean ⫾ SD) (ANCOVA statistical analysis of differences between pre- and post-intervention
values for the LW, IW, SW and C groups; where parametric analysis was not possible the GLM results are given)
n
HDL-C (mmol/l)
males
LW
IW
SW
C
females
LW
IW
SW
C
TC/HDL-C
males
LW
IW
SW
controls
females
LW
IW
SW
controls
LDL-C/HDL-C
males
LW
IW
SW
controls
females
LW
IW
SW
C
Pre-intervention
Post-intervention
5
3
3
4
1.10
1.25
1.09
1.23
(0.52)
(0.32)
(0.07)
(0.27)
1.28
1.36
1.44
1.32
(0.37)
(0.28)
(0.26)
(0.23)
0.18
0.11
0.35
0.09
13
7
10
8
1.64
1.45
1.68
1.54
(0.45)
(0.23)
(0.36)
(0.49)
1.64
1.53
1.71
1.51
(0.40)
(0.13)
(0.41)
(0.55)
0.00
0.08
0.03
–0.03
GLM 0.731
5
3
3
4
5.46
4.76
4.60
4.42
(1.27)
(1.31)
(0.97)
(0.71)
4.71
3.83
3.42
4.28
(1.28)
(0.44)
(0.46)
(0.80)
–0.75
–0.93
–1.18
–0.14
0.113
13
7
10
8
3.84
4.03
3.85
4.13
(1.66)
(0.58)
(1.35)
(1.40)
3.57
3.77
3.77
4.34
(1.56)
(0.61)
(1.30)
(1.60)
–0.27
–0.26
–0.08
0.21
GLM 0.098
5
3
3
4
5.26
4.33
4.17
3.84
(1.54)
(1.66)
(1.23)
(0.88)
4.38
3.14
2.76
3.78
(1.54)
(0.50)
(0.56)
(1.01)
–0.88
–1.19
–1.41
–0.06
0.108
13
7
10
8
3.25
3.33
3.18
3.59
(1.92)
(0.68)
(1.05)
(1.68)
2.98 (1.78)
3.08 (0.73)
3.11 (1.43)
3.93 (2.02)
–0.27
–0.25
–0.07
0.34
0.098
IWmale versus SWmale versus Cmale) for LDL-C,
TC/HDL-C or LDL-C/HDL-C (P ⬎ 0.2). However,
the female sub-groups (LWfemale versus IWfemale
versus SWfemale versus Cfemale) showed heterogeneity of variance. Therefore the Kruskal–Wallace
non-parametric test was employed, and revealed
no significant difference between baseline levels
for HDL-C, TC/HDL-C and LDL-C/HDL-C
(P ⬎ 0.4).
Post-intervention ANCOVA analysis revealed
significant decreases in the amount of LDL-C (P ⬍
0.03), apo A-II (P ⬍ 0.02) and increase in the
Mean difference
P
0.178
ratio of apo A-I/A-II (P ⬍ 0.05). A one-way
ANOVA and post hoc Scheffe test identified that
the LW and IW groups had significantly reduced
concentrations of LDL-C and apo A-II compared
to C. This analysis also showed that the significant
increase in the ratio of apo A-I/A-II was only
apparent in the LW group, although the IW and
SW did show mean increases. There were no other
significant differences (P ⬎ 0.05) in the other
factors which were not analysed separately for
males and females.
For those factors for which pre-intervention
811
K. Woolf-May et al.
gender differences had been demonstrated
(HDL-C, TC/HDL-C and LDL-C/HDL-C) the
homogeneity of variance of the amount of change
was again calculated. For the females (LWfemale
versus IWfemale versus SWfemale versus Cfemale)
homogeneity of variance was only achieved for
LDL-C/HDL-C which subsequently revealed no
significant difference (P ⬎ 0.1) between the groups.
The male data showed homogeneity in all factors;
however, analysis found no significant difference
(P ⬎ 0.5) between the groups within these factors.
There were indications of a possible trend (P ⫽
0.098–0.113) in the amount of change in TC/
HDL-C and LDL-C/HDL-C with mean reductions
in all walking groups (TC/HDL-C, males: LW
13.7%, IW 19.5% and SW 25.6%; females: LW
7.0%, IW 6.5% and SW 2.1%; LDL-C/HDL-C,
males: LW 16.7%, IW 27.5% and SW 33.8%;
females: LW 8.3%, IW 7.5% and SW 2.2%) with
the C group showing very little change (males
showing a decrease of 3.2 and 1.6%, and females
showing an increase of 4.8 and 8.7%, respectively).
However, given that these data did not reach
statistical significance, no conclusions may be
reached and further investigation is required. There
were no indications of potential changes in HDL-C.
Discussion
The heart rate responses during all the walking
programmes complied with the ACSM (ACSM,
1995) guidelines and supported the findings of
Porcari et al. (Porcari et al., 1987) who ascertained
that brisk walking was sufficient to attain the
required exercise heart rate in older, low-active
individuals. The volume of exercise performed was
relatively moderate and of a type which could
be accommodated into many individuals’ weekly
routine, a factor which is likely to have the added
benefit of greater compliance (Jette et al., 1988;
McPhillips et al., 1989; Hillsdon et al., 1995;
Aarts, et al., 1997). From the analysis it was
apparent that the walking programmes were similar
in terms of the total volume of walking (minutes
per week) and the intensity of the exercise (heart
rate whilst walking), but differed in the length of
812
each walking bout and the frequency with which
subjects walked on a daily basis.
The similar changes in aerobic fitness produced
by all walking groups suggest that fitness benefits
may be gained from walking 149–157 min/week,
but that the length of each individual walking bout
(group averages of 10, 15 and 39 min during the
final 10 weeks) contributing to this volume did not
seem to affect the results. Consequently, all the
walking interventions utilized in this study
appeared to be effective at improving aerobic
fitness which has been shown to be a significant
factor in reducing the risk of all cause mortality
(Blair et al., 1995). The implications of this are to
support the potential for short accumulated bouts
of walking to be prescribed as a means of improving
aerobic fitness in a way that may be more easily
incorporated into an individual’s lifestyle (Hillsdon
et al., 1995).
The analysis of HDL-C, apo A-I, TC/HDL-C
and LDL-C/HDL-C revealed more favourable preintervention values in the females when compared
to the male subjects, which supported the previous
findings of Kannel (Kannel, 1987) who reported
gender differences in some of these factors.
The post-intervention analysis revealed statistically significant reductions in LDL-C for the LW and
IW groups, 5.8 and 8.3%, respectively; compared to
a mean increase of 4.2% in the C group and a
non-statistically significant reduction of 2.6% in
the SW group. These findings were similar to those
observed in a study carried out by Palank and
Hargreaves (Palank and Hargreaves, 1990). The
statistically significant decrease in apo A-II for the
LW group (also seen in the IW group) would
appear to be the main contributor in the significant
increase in the ratio of A-I/A-II for the LW group
and although this implies that apo A-I did not
increase per se it would indicate a change in
the protein component of the HDL particle. This
according to some studies would suggest a greater
cardio-protective effect for the walkers in terms of
an enhanced efflux of cholesterol from the artery
walls (Mahlberg, et al., 1991; Rothblat et al., 1992).
The failure of the study to find any changes in
HDL-C is contrary to the findings of other studies
Brisk walking to improve aerobic fitness
which used walking regimens of similar intensity
and ‘traditional’ design to that of the LW
group [60% predicted HR max (Hardman et al.,
1989), 63–67% predicted HR max (Carlota, 1990),
6.4 km/h (Duncan et al., 1991), 70–80% predicted
HR max (Whitehurst and Menendez, 1991),
6.4 km/h (Hardman and Hudson, 1994)]. This may
be related to the relatively good pre-intervention
values of the subjects (Woolf-May et al., 1998).
Reducing the risk of cardiovascular disease by
reducing LDL-C concentration and other factors
is important in terms of public health (American
Heart Association, 1990) and the beneficial change
in LDL-C, as seen from this and other studies
(Palank and Hargreaves, 1990), might be more
important for the sedentary/low-active members of
our society. Consequently, being over-concerned
with increases in HDL-C may not be necessary in
this context, especially if increases in the ratio of
apo A-I/A-II can be achieved. Therefore, it would
appear that similar beneficial changes in LDL-C
may be achieved from walking in bouts of 15 min
compared to the traditional 20–40 min exercise
bout. However, walking in bouts of about 10
min or less would appear to have little effect in
provoking changes in blood lipid profiles.
The findings of this study have demonstrated
that benefits to aerobic fitness may be achieved
from all the walking regimens. However, whilst
these changes may be similar for aerobic fitness
they are not for blood lipid profile. It would appear
that the greatest health benefit may be gained from
the LW regimen followed by that of the IW,
with the SW being least effective. Although for
sedentary/low-active members of the population
any improvement in these factors may be considered as desirable. Furthermore, these findings
have demonstrated that these changes may be
achieved from walking briskly in bouts of 15 min
or more over a relatively short time span (18
weeks) for about 150–175 min/week (approximately 16 km/week). This is a volume and mode of
exercise which could be accommodated into many
individual’s weekly routine (Hillsdon et al., 1995).
Consequently, these findings suggest that fitness
and health benefits may be gained from moderate
intensity exercise accumulated in 15 min bouts
during a day and could provide an effective exercise
prescription for those who find it difficult to achieve
the traditionally prescribed 20–30 min prolonged
bout of physical activity. However, it is acknowledged that not all CHD risk factors or components
of fitness were assessed in this study and therefore
additional research is needed to elucidate the
breadth of benefits which may be gained from
accumulated exercise bouts.
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815