164
Journal of Exercise Physiologyonline
February 2017
Volume 20 Number 1
Editor-in-Chief
Official Research Journal of
the American
Society
of
Tommy
Boone, PhD,
MBA
Review
Board
Exercise
Physiologists
Todd Astorino, PhD
ISSN 1097-9751
Julien Baker,
PhD
Steve Brock, PhD
Lance Dalleck, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Yit Aun Lim, PhD
Lonnie Lowery, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Robert Robergs, PhD
Chantal Vella, PhD
Dale Wagner, PhD
Frank Wyatt, PhD
Ben Zhou, PhD
Official Research Journal
of the American Society of
Exercise Physiologists
ISSN 1097-9751
JEPonline
Speed of Walking on Aerobic Capacity and Coronary
Heart Disease (CHD) Risk Profiles in Obese Females
Sitha Phongphibool1, Thanomwong Kritpet1, Ornchuma Hutagovit2
1
Faculty of Sports Science, Chulalongkorn University, Bangkok,
Thailand, 2Department of Physical Therapy and Rehabilitation,
Chaleonkrungprachaluk Hospital, Bangkok, Thailand
ABSTRACT
Phongphibool, S, Kritpet, T, Hutagovit, O. Speed of Walking on
Aerobic Capacity and Coronary Heart Disease (CHD) Risk Factors in
Obese Females. JEPonline 2017;20(1):164-176. The purpose of
this study was to determine the effects of speed of walking on
aerobic capacity (VO2 peak) and coronary heart disease (CHD) risk
profiles in 30 sedentary obese females aged 50.2 ± 4.6 yrs old with
at least 2 CHD risk factors. The subjects were randomly divided into
two groups: (a) speed walking group; and (b) self-paced walking
group. Measurements of aerobic capacity and CHD risk profiles were
performed at baseline and post-training. Incremental Treadmill Walk
Test (ITWT) was only performed in the speed walking group to
assess maximal walking speed. All subjects underwent a 10-wk
walking intervention. After 10 wks of walking, the results showed that
the speed walking group improved in VO2 peak (P<0.01), resting
heart rate (P<0.01), total cholesterol (P<0.05), and triglycerides
(P<0.05) at post-training. The self-paced walking group exhibited
significant improvements in resting heart rate (P<0.05), resting
systolic blood pressure (P<0.01), and resting diastolic blood
pressure (P<0.05) at post-training. Furthermore, the speed walking
group exhibited significant absolute improvements in VO2 peak
(P<0.01), total cholesterol (P<0.05), and triglycerides (P<0.05) when
compared to the self-paced walking group. Speed of walking
significantly improves aerobic capacity and certain CHD risk profiles
in sedentary obese females.
Key Words: Aerobic Capacity, CHD Risks, Obesity, Walking Speed
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INTRODUCTION
Coronary heart disease (CHD) is the most common cause of death globally. The number of
individuals affected by CHD is increasing in both industrialized and developing countries. The
condition is caused by the buildup of plaque in the coronary arteries, and is believed to be
linked to the inflammation process called atherosclerosis. The cause of CHD is multifactorial
and many believe that risk factors such as physical inactivity, high blood pressure,
cholesterol, triglycerides, LDL-cholesterol, HDL-cholesterol, and CRP (inflammatory marker)
contribute to the occurrence of this condition (1,2,6,9). Targeting the risk factors that
contribute to the development of CAD can alter the clinical course of the disease (3,14).
Regular participation in physical activity is associated with reduced risk of many noncommunicable diseases including CHD and can also modify the risk factors that contribute to
the onset of CHD. Walking is a form of physical activity, when perform routinely, can result in
physiological benefits such as improve cardiorespiratory fitness, improve physical endurance,
and reduce abdominal fat (4,6,12,21). In particular, Tully et al. (27) reported favorable effects
of brisk walking on cardiovascular risks.
Brisk walking is a relative term, and it can be slow for some and hard for others (4,5,20,21).
Thus, to prescribe brisk may not be a sufficient stimulus for some individuals and might be
over exerted for others (15). Consequently, walking at a fixed relative speed to an individual’s
maximal walking speed might be a preferred choice in order to elicit changes in aerobic
capacity and the CHD risk profile. Therefore, the purpose of this study was to assess the
impact of walking speed on aerobic capacity (VO2 peak) and CHD risk factors in middle-aged
obese women.
METHODS
Subjects
Thirty sedentary obese female hospital employees with the mean age of 50.2 ± 4.6 yrs old
(range, 41 to 58 yrs old) with at least 2 risk factors for CHD (i.e., elevated blood pressure,
fasting blood glucose, dyslipidemia, high waist circumference, and overweight or obese) were
recruited to participate in this study. The obesity classification was in accordance with WHO
Asian guidelines: ≥23 kg·m-2 is overweight; >25 kg·m-2 is obese (31). The subjects were
contacted by the primary investigator by telephone to provide the details of the study and the
time involvement. The subjects were invited to the orientation session where they filled out a
health questionnaire, underwent a physical examination, and blood chemistry phlebotomy.
To be included in the study, the subjects had to be free of hypertension, diabetes mellitus
(DM), orthopedic, and neuromuscular problems. Prior to signing the inform consent, all
subjects were informed verbally and in writing as to the length of the study, experimental
protocol, and the risk of involvement. Then, the subjects were scheduled to return to the
laboratory within 48 to 72 hrs to undergo the aerobic capacity assessment and the
Incremental Treadmill Walk Test (ITWT). The study protocols and procedures were approved
by the Research Ethics Review Committee for Research Involving Research Participants,
Health Science Group, Chulalongkorn University, Thailand.
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Procedures
All subjects were assessed for anthropometric measurements that included height, weight,
and body composition. Blood chemical profile of fasting blood glucose, total cholesterol,
triglycerides, LDL-cholesterol, HDL-cholesterol, and hs-CRP were measured via laboratory
analysis. The subjects were randomly assigned to two walking groups for the duration of the
10-wk study: (a) the speed walking group that required the subjects to walk on a treadmill at
the hospital fitness center 7 d·wk-1 for 30 min·session-1 at 80% of the speed achieved during
the ITWT; and (b) the self-paced walking group that walked on level ground 7 d·wk-1 for 30
min·session-1 at home or their place of choice at their convenience. Both groups were
instructed to walk at the same frequency and duration per week, and they were advised to
maintain a normal dietary pattern during the study. All subjects performed aerobic capacity
assessment at baseline and post-training, but only the speed walking group underwent the
Incremental Treadmill Walking Test (ITWT) to assess maximal walking speed at baseline.
Anthropometric Measurements
Waist and hip circumference was measured in centimeters with an anthropometric tape.
Waist circumference was assessed at the horizontal plane of the iliac crest. The hip
circumference was taken at the largest posterior extension of the buttocks. The waist to hip
ratio was calculated from these measurements.
Body Composition
Body composition was assessed by instructing the subjects to empty their pockets and to
take off their shoes and socks. They were then instructed to step on the scale and remain on
a digital body composition analyzer (Tanita BC-533, Japan) that measured and analyzed
body weight (kg), fat-free mass (kg), fat mass (kg), and body fat (percentage). Body Mass
Index (BMI) was calculated by dividing body weight in kilogram (kg) by height in meter square
(m2).
Resting Heart Rate and Resting Blood Pressure
To assessing resting heart rate, the subjects’ chests were fitted with a wireless heart rate
monitor (Polar H7, Finland). The subjects were asked to sit down quietly and undisturbed for
5 min. Heart rate was taken after it was stabilized at a lowest rate. For resting blood pressure
measurement, the subjects were instructed to sit in a chair with the left arm resting on the
table with the elbow slightly flexed. The blood pressure cuff was placed the left biceps and
the resting blood pressure was taken with an automatic blood pressure monitor (Omron SEM1, Japan).
Aerobic Capacity
The subjects were asked to report to the Sports Science and Health laboratory at the Faculty
of Sports Science, Chulalongkorn University for testing. Upon arrival, the subjects were
instructed to sit quietly and physiological baseline was measured. The subjects’ chests were
fitted with a wireless heart rate monitor (Polar H7, Finland) to assess the resting heart rate.
Blood pressure was taken with an automatic blood pressure monitor (Omron SEM-1, Japan).
The subjects were informed of the exercising testing procedures and the test precautions. All
questions that the subjects had pertaining to the exercise test were answered and clarified.
Prior to the testing, the open circuit spirometry metabolic system (Cortex Metamax 3BR2,
Germany) was calibrated according to the manufacture specifications and recommendations.
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Each subject was attached with a facemask, hooked up to the metabolic system, and was
instructed to stand still for baseline physiological measurements on a motorized treadmill (hpcosmo 4.0, Germany). Using the ramped Bruce protocol (29) and gas analysis system, each
subject’s maximal aerobic capacity was determined. The treadmill speed and incline were
changed every 15 sec until the subject’s maximal capacity was reached. During the test,
blood pressure was assessed every 2 min with the palm aneroid sphygmomanometer (MDF
Bravata, USA). Exercise heart rate was recorded every minute (Polar H7, Finland). The
subject’s oxygen consumption (VO2), carbon dioxide production (VCO2), ventilation (VE),
respiratory exchange ratio (RER), and oxygen pulse (VO2/HR) were continually monitored.
Verbal encouragement was provided throughout the test and maximal aerobic capacity was
determined by averaging the highest 30 sec of VO2 that was obtained during the test. Testing
was terminated in accordance with standard guidelines (1).
Incremental Treadmill Walk Test (ITWT)
After a 20 min rest from the aerobic capacity assessment, each subject in the intervention
group underwent the ITWT to determine the maximal walking speed (26). Maximal walking
speed was defined as a condition in which a subject was unable to maintain an appropriate
walking pace. Thus, the subject resorted to running to keep up with the treadmill’s speed
(26). Prior to initiating the test, each subject was fitted with a wireless heart rate monitor
(Polar H7, Finland) and a facemask. Then, the subject was hooked up to the open circuit
spirometry metabolic system (Cortex Metamax 3BR2, Germany). After standing still for the
determination of resting physiological data, the subject was instructed to walk on the treadmill
starting at 2.5 mi·hr-1 with no incline. The speed was increased 0.4 mi·hr-1 every 3 min until
the subject was unable to maintain the appropriate walking technique (i.e., no race walking,
jogging, or running). Gas analysis was used to determine the subject’s VO2 and other
physiological responses at maximal walking velocity.
After completion of the ITWT, each subject rested for at least 15 min until the physiological
responses (i.e., HR and BP) returned to baseline. Then, the subject underwent an additional
walk test to determine the speed at 80% of maximal walking velocity that was obtained from
the ITWT for 15 min each to determine oxygen cost and other physiological responses of
walking at that intensity.
Walking Program
The subjects were randomly divided into two groups for the 10 wks walking study: the speed
walking group and the self-paced walking group. To standardize the walking program, each
group was given the same protocol of frequency and duration of walking per week for the
duration of the study. The subjects in the speed walking were given a specific walking speed
that was obtained previously during the ITWT. They were instructed to engage in treadmill
walking at a specified speed at the hospital fitness center. Likewise, the subjects in the selfpaced walking were advised to engage in level ground walking on a daily basis. Both groups
were instructed to walk continuously for 30 min·session-1 7 d·wk-1. All subjects were advised
to maintain their normal dietary pattern. Each subject was contacted periodically by the
primary investigator to discuss any difficulties during the 10-wk study.
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Blood Chemistry
After the 10-hr fast, the subjects’ blood samples were collected from the antecubital vein
while in the sitting position to obtain plasma glucose, total cholesterol (TC), triglycerides (TG),
LDL-Cholesterol (LDL-C), HDL-Cholesterol (HDL-C), and high sensitivity C-Reactive Protein
(hs-CRP). The plasma glucose, total cholesterol, triglycerides, LDL-Cholesterol, and HDLCholesterol were analyzed using the enzymatic color test (Beckman Coulter UA 480, USA).
The high sensitivity C-Reactive Protein variable was analyzed using the particle enhanced
immunoturbidimetric assay (Roche Cobas C501, USA). All blood draws and analyses were
performed at the Faculty of Allied Health Sciences Laboratory at Chulalongkorn University.
Statistical Analyses
Descriptive statistics were used to analyze the subjects’ baseline characteristics. The
variables are presented as the mean ± SD. Differences within a group (intra-group) were
assessed by comparing variables at baseline with the 10-wk data of walking. The extent of
the change in variables was calculated by subtracting the baseline results from the 10-wk
results. The differences in variables between the two groups were compared using the
independent t-test. Statistical significance was set at P<0.05. All statistical analyses were
performed using SPSS statistical software version 23 (IBM SPSS Inc., Chicago, USA).
RESULTS
Descriptive characteristics of the subjects in the speed walking and self-paced groups are
presented Table 1. The subjects in the two groups were similar in most variables at baseline.
However, the speed walking group exhibited significantly higher BMI at baseline than the selfpaced group (P<0.05).
Table 1. Baseline Characteristics of Study Groups.
Total
(N = 30)
Speed Walking
(n = 15)
Self-Paced
(n = 15)
VO2 peak (mL·kg-1·min-1)
22.4 ± 2.9
21.8 ± 2.9
22.9 ± 2.9
Age (yr)
50.1 ± 4.7
50.0 ± 5.6
50.2 ± 3.9
Height (cm)
155.7 ± 4.6
155.7 ± 5.5
155.6 ± 3.7
Weight (kg)
65.1 ± 8.7
68.1 ± 10.9
62.1 ± 4.3
BMI (kg·m-2)
26.8 ± 2.9
28.0 ± 3.6*
25.6 ± 1.1
Waist (cm)
88.3 ± 6.4
89.4 ± 8.4
87.1 ± 3.5
104.9 ± 7.2
104.4 ± 9.5
105.3 ± 4.1
.84 ± .05
.86 ± .06
.83 ± .04
%Body Fat
35.3 ± 3.6
35.9 ± 4.3
34.7 ± 2.8
Resting HR (beats·min-1)
85.2 ± 7.9
87.5 ± 8.7
82.8 ± 6.5
Variable
Hip (cm)
WHR
169
Max HR (beats·min-1)
163.8 ± 10.3
161.6 ± 12.9
166.1 ± 6.5
Resting SBP (mmHg)
131.2 ± 12.3
128.7 ± 14.1
133.6 ± 10.8
Resting DBP (mmHg)
76.3 ± 8.0
76.8 ± 6.9
76.7 ± 9.2
FBG (mg·dL-1)
101.2 ± 14.3
99.8 ± 9.2
102.6 ± 18.4
TC (mg·dL-1)
231.1 ± 53.2
237.1 ± 49.2
225.1 ± 58.0
TG (mg·dL-1)
128.9 ± 47.6
141.7 ± 52.9
116.1 ± 39.2
-1
145.7 ± 40.6
147.5 ± 36.1
143.8 ± 45.8
-1
59.9 ± 10.9
58.8 ± 13.5
61.1 ± 8.0
TC/HDL-C
4.0 ± 1.2
4.2 ± 1.2
3.8 ± 1.3
hs-CRP (mg·dL-1)
2.2 ± 2.4
2.8 ± 3.0
1.7 ± 1.4
LDL-C (mg·dL )
HDL-C (mg·dL )
Values are mean ± SD; BMI = Body Mass Index; WHR = Waist to Hip Ratio; Resting HR = Resting Heart
Rate; Max HR = Maximal Heart Rate; Resting SBP= Resting Systolic Blood Pressure; Resting DBP =
Resting Diastolic Blood Pressure; VO2 peak = Peak Oxygen Consumption; FBG = Fasting Blood Glucose;
TC = Total Cholesterol; TG = Triglycerides; LDL-C = Low Density Lipoprotein Cholesterol; HDL-C = High
Density Lipoprotein Cholesterol; TC/HDL = Total Cholesterol to High Density Lipoprotein Cholesterol Ratio;
hs-CRP = High Sensitivity C-Reactive Protein; *P<0.05
After 10 wks of the walking intervention, the speed walking group showed significant
improvements in VO2 peak (P<0.01), resting heart rate (P<0.01), total cholesterol (P<0.05),
and triglycerides (P<0.05) at post-training. Conversely, the self-paced walking group
exhibited significant improvements in resting heart rate (P<0.05), resting systolic blood
pressure (P<0.01), and resting diastolic blood pressure (P<0.05) at post-training as
presented in Table 2.
Table 2. Change in Fitness, Body Weight, Body Composition, and Blood Chemistry
between Baseline and Post-Training in Speed Walking and Self-Paced Groups.
Variables
VO2 peak (mL·kg-1·min-1)
Speed walking
Self-Paced
Weight (kg)
Speed walking
Self-Paced
BMI (kg·m-2)
Speed walking
Self-Paced
Waist (cm)
Speed walking
Self-Paced
Pre-training
Post-Training
t
P-Value
21.8 ± 2.9
22.9 ± 2.9
25.2 ± 3.4**
23.7 ± 3.2
-6.730
-1.922
.000
.075
68.1 ± 10.9
62.1 ± 4.3
67.9 ± 11.2
61.4 ± 4.1
.703
1.543
.494
.145
28.0 ± 3.6
25.6 ± 1.1
27.9 ± 3.9
25.3 ± 1.3
.940
1.546
.363
.144
89.4 ± 8.4
87.1 ± 3.5
87.1 ± 6.2
86.4 ± 4.3
2.088
1.022
.056
.324
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Hip (cm)
Speed walking
Self-Paced
WHR
Speed walking
Self-Paced
%Body Fat
Speed walking
Self-Paced
Resting HR (beats·min-1)
Speed walking
Self-Paced
Resting SBP (mmHg)
Speed walking
Self-Paced
Resting DBP (mmHg)
Speed walking
Self-Paced
FBG (mg·dL-1)
Speed walking
Self-Paced
TC (mg·dL-1)
Speed walking
Self-Paced
TG (mg·dL-1)
Speed walking
Self-Paced
LDL-C (mg·dL-1)
Speed walking
Self-Paced
HDL-C (mg·dL-1)
Speed walking
Self-Paced
TC/HDL-C
Speed walking
Self-Paced
hs-CRP (mg·dL-1)
Speed walking
Self-Paced
104.4 ± 9.5
105.3 ± 4.0
102.9 ± 8.2
104.5 ± 4.2
2.238
1.309
.052
.212
.86 ± .06
.83 ± .04
.85 ± .05
.83 ± .04
1.182
.186
.257
.855
35.9 ± 4.3
34.7 ± 2.8
35.4 ± 3.5
34.0 ± 4.1
.897
1.138
.385
.274
87.5 ± 8.7
82.8 ± 6.5
80.8 ± 8.7**
76.4 ± 5.7**
3.790
4.326
.002
.001
128.7 ± 14.1
133.6 ± 10.8
121.5 ± 13.7
127.3 ± 8.3**
1.935
3.201
.073
.006
76.8 ± 6.9
76.7 ± 9.2
77.0 ± 6.8
73.5 ± 7.5*
-.097
2.567
.924
.022
99.8 ± 9.2
102.6 ± 18.4
96.7 ± 14.7
102.5 ± 18.3
1.225
.127
.241
.900
237.1 ± 49.2
225.1 ± 58.0
211.4 ± 33.7*
224.6 ± 62.4
2.143
.161
.050
.874
141.7 ± 52.9
116.1 ± 39.2
115.1 ± 33.3*
121.6 ± 36.2
2.474
-1.742
.027
.103
147.5 ± 36.1
143.8 ± 45.8
128.5 ± 30.4
144.1 ± 47.3
1.592
-.098
.134
.923
58.8 ± 13.5
61.1 ± 8.0
58.5 ± 13.9
60.9 ± 8.1
.142
.356
.889
.727
4.2 ± 1.2
3.8 ± 1.3
3.8 ± 1.1
3.8 ± 1.5
1.487
-.225
.159
.825
2.8 ± 3.0
1.71 ± 1.4
2.4 ± 1.9
1.5 ± 1.1
.984
1.196
.342
.252
Values are mean ± SD; BMI = Body Mass Index; WHR = Waist to Hip Ratio; Resting HR = Resting Heart Rate;
Resting SBP= Resting Systolic blood pressure; Resting DBP = Resting Diastolic Blood Pressure; VO2peak =
Peak Oxygen Consumption; FBG = Fasting Blood Glucose; TC = Total Cholesterol; TG = Triglycerides; LDL-C
= Low Density Lipoprotein Cholesterol; HDL-C = High Density Lipoprotein Cholesterol; TC/HDL = Total
Cholesterol to High Density Lipoprotein Cholesterol Ratio; hs-CRP = High Sensitivity C-Reactive Protein;
*P<0.05; **P<0.01
The absolute change in fitness, body composition, and blood chemistry are presented in
Table 3. After 10 wks of walking intervention, the speed walking group exhibited significant
171
improvements in absolute change in VO2 peak (P<0.01), total cholesterol (P<0.05), and
triglycerides (P<0.05) when compared to the self-paced walking group.
Table 3. Absolute Change in Fitness, Body Weight, Body Composition, and Blood
Chemistry between Baseline and Post-Training in Speed Walking and Self-Paced
Groups.
Variables
VO2 peak (mL·kg-1·min-1)
Speed
Walking
3.4 ± 1.9**
Self-Paced
t
P-Value
.80 ± 1.6
3.972
.000
Weight (kg)
-.15 ± .85
-.68 ± 1.7
1.071
.297
-2
BMI (kg·m )
-.12 ± .49
-.28 ± .70
.733
.470
Waist (cm)
-2.4 ± 4.4
-.67 ± 2.5
-1.300
.204
Hip (cm)
-1.6 ± 2.7
-.80 ± 2.3
-.825
.416
WHR
-.01 ± .03
.00 ± .01
-1.101
.285
-.53 ± 2.3
-.71 ± 2.4
.208
.836
Resting HR (beats·min )
-6.7 ± 6.8
-6.4 ± 5.7
-.144
.886
Resting SBP (mmHg)
-7.2 ± 14.4
-6.3 ± 7.6
-.222
.826
Resting DBP (mmHg)
.20 ± 7.9
-3.2 ± 4.8
1.416
.168
-3.1 ± 9.9
-.13 ± 4.1
-1.086
.287
-25.7 ± 46.5*
-.47 ± 11.2
-2.045
.050
%Body Fat
-1
FBG (mg·dL-1)
TC (mg·dL-1)
TG (mg·dL-1)
-26.6 ± 41.6**
5.5 ± 12.1
-2.863
.011
-1
-19.0 ± 46.2
.33 ± 13.2
-1.558
.138
-1
- .27 ± 7.3
-.20 ± 2.2
-.034
.973
TC/HDL-C
-.41 ± 1.1
.01 ± .34
-1.426
.165
hs-CRP (mg·dL-1)
-.41 ± 1.6
-.25 ± .82
-.343
.734
LDL-C (mg·dL )
HDL-C (mg·dL )
Values are mean ± SD; BMI = Body Mass Index; WHR = Waist to Hip Ratio; Resting HR = Resting Heart Rate;
Resting SBP= Resting Systolic Blood Pressure; Resting DBP = Resting Diastolic Blood Pressure; VO2 peak =
Peak Oxygen Consumption; FBG = Fasting Blood Glucose; TC = Total Cholesterol; TG = Triglycerides; LDL-C
= Low Density Lipoprotein Cholesterol; HDL-C = High Density Lipoprotein Cholesterol; TC/HDL = Total
Cholesterol to High Density Lipoprotein Cholesterol Ratio; hs-CRP = High Sensitivity C-Reactive Protein;
*P<0.05; **P<0.01
DISCUSSION
Walking on Aerobic Capacity
Cardiorespiratory fitness (CRF), quantified by VO2 peak, is associated with a reduced
mortality risk (2,3,9,10,11,18,23). Meta-analysis shows that for each MET increase in CRF is
associated with a 15% reduction in risk of all-cause mortality and 13% reduction in risk of
CVD and CHD events (3,10). Fit individuals have lower all-cause and CVD mortality risk than
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unfit counterparts, regardless of adiposity classification (2,9,10). Furthermore, improvement
in cardiorespiratory fitness translates to a better survival and better prognosis in those with
medical conditions (18,23,30). According to Myers (22), VO2 peak is a superior predictor of
mortality compared with tobacco use, hypertension, dyslipidemia, and diabetes in subjects
with or without a confirmed diagnosis of cardiovascular disease (22). Exercise training at
sufficient intensity, frequency, and duration is a cornerstone for improving CRF and health,
and it has been shown to provide cardio-protective effects against CHD (9,10).
The 10-wk walking study showed that the obese female subjects in the speed walking group,
who walked at 80% of their maximal walking speed, significantly improved VO2 peak at posttraining (P<0.01). Conversely, the obese female subjects in the self-paced walking group did
not improve in VO2 peak at post-training. The improvement in VO2 peak at post-training in the
speed walking group was due to the intensity of walking that was sufficient to cause the
physiological changes that affect cardiorespiratory fitness. The changes include improvement
in stroke volume, cardiac output, increase in muscles capillary density and mitochondria, and
better oxygen extraction (28). The change in VO2 peak occurs in a dose response manner,
meaning that faster walking results in better improvement in fitness when compared to a
slower walking speed (20,27). Our findings are in agreement with Duncan et al. (4) that
looked at the fitness response in the three walking groups: strollers, brisk walking, and
aerobic walking. Their results showed that aerobic walking resulted in the greatest change in
VO2 max when compared to other walking groups and no significant change in VO2 max was
detected in the control group at the end of the study.
Our study also revealed that the absolute change in VO2 peak in the speed walking group
was significantly higher than the self-paced walking groups after the 10 wks of intervention
(P<0.01). The speed walking group exhibited an absolute change in VO2 peak that was
approximate to a 1 MET improvement from baseline. This level of change supports clinical
importance in terms of all-cause of mortality risk reduction (2,9,10). Evidence shows that the
progressive decrease in mortality risk in transition from lower to higher fitness categories.
Overall, there was a 13% decrease in mortality risk per MET increase in aerobic capacity
(9,23). Thus, the improvement is likely to decrease the risk of future cardiovascular events in
this group of obese females if they are able to maintain this level of fitness. For those
interested in obtaining meaningful change in cardiorespiratory fitness, walking at a faster
pace will result in an improvement in fitness as seen in the improvement in VO2 peak in the
present study.
Walking on Resting Heart Rate and Blood Pressure
After 10 wks of walking, both walking groups exhibited a significant reduction in resting heart
rate at post-training (P<0.01). This decrease in resting heart was is due to the change in
parasympathetic activity (vagal tone) and the improvement in the heart preload, which results
in an increase in stroke volume as the body adapts to regular walking (28). This physiological
change occurs in those who engage in regular exercise program regardless of age, gender,
or race (11,28).
A meta-analysis of randomized control trials shows that regular walking has been shown to
improve resting systolic and diastolic blood pressure in those with elevated blood pressure
(21). However, our findings did not hold true for both walking groups. Our results revealed
that only the self-paced walking group showed a significant reduction in both resting systolic
173
blood pressure (P<0.01) and diastolic blood pressure (P<0.05) while no significant change
was detected in the speed walking group. Tully et al. (27) compared the effects of brisk
waking and regular habitual lifestyle on fitness and cardiovascular risk. They discovered that
brisk walking for 12 wks resulted in a significant improvement in resting systolic (P<0.05) and
diastolic (P<0.01) blood pressure. Despite the improvement observed in the past study, our
data on resting blood pressure at post-training in the speed walking group did not show a
similar result despite the relative fast walking speed being imposed. The fact that no change
was found in systolic and diastolic blood pressure may be due to the fact that the speed
walking group entered the study with a low baseline blood pressure. However, the self-paced
walking group significantly reduced systolic and diastolic blood pressure at post-training. The
change in blood pressure may have been the result of the increase in physical activity in this
group of obese females as these subjects were sedentary prior to joining the study. The
change in resting blood pressure was also attributed to an increase in vasoactive substances
that increase vasodilation, alteration of vascular structure that increases lumen diameter, and
reduction in peripheral resistance (12). The previous perspective study reported that the
reduction in blood pressure would result in lower stroke, ischemic heart disease, and other
vascular cause mortalities in middle-age individuals (24)
Walking on CAD Risk Factors
After 10 wks of walking, our results indicate that there was a significant decrease in TC
(P<0.05) and TG (P<0.05) in the speed walking group at post-training while the self-paced
walking group failed to exhibit any significant change in the lipid and lipoproteins profiles.
When the absolute changes in lipid and lipoproteins profiles were compared between the two
groups, the speed walking group also exhibited significant absolute change in TC and TG
(P<0.05). The change in TC and TG in the speed walking group may have been attributable
to the intensity of walking. This group was prescribed the walking speed at 80% of maximal
walking speed that corresponds to the intensity of 72% of VO2 peak, which is categorized as
hard (25). Walking at this level of intensity would yield higher energy expenditure during
exercise in this group and higher fatty acid oxidation (25,28). Previous studies have shown
that the reduction in TC and TG occurred due to sufficient energy expenditure, previous level
of physical activity, and the initial baseline values (6-8). Our obese females in the speed
walking group entered the study with higher baseline in TC and TG when compared to the
subjects in the self-paced-walking group. This may explain the change in these two variables
at post-training.
CONCLUSIONS
The findings indicate that the speed of walking improves aerobic capacity (VO2 peak) and
also affects the CHD risk profile such as resting HR, SBP, DBP, TC, and TG. The data
suggest that walking at a specific speed results in a better outcome when compared to the
self-paced walking speed. Thus, when prescribing walking as a form of regular exercise, it is
advantageous to specify optimal walking speed so that a sufficient stimulus can be achieved
and positive outcome can be realized.
174
ACKNOWLEDGMENTS
The authors would like to thank you the subjects for their tireless participation. Without their
contributions, this study would not have been possible. To Banbung Hospital, thank you for
allowing the subjects to use the hospital Fitness Center for exercise. In additions, the authors
would like to thank you the Faculty of Sports Science, Chulalongkorn University for permitting
the usage of the laboratory equipment. This study was supported by the Faculty of Sports
Science Research Fund.
Address for correspondence: Thanomwong Kritpet, PhD, Faculty of Sports Science,
Chulalongkorn University, RamaI Road, Patumwan, Bangkok 10330, THAILAND. Tel.
+6681-813-1970. Email: [email protected]
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