Journal of Exercise Physiologyonline

February 2017Volume 20 Number 1

Editor-in-ChiefTommy Boone, PhD, MBAReview BoardTodd Astorino, PhDJulien Baker, PhDSteve Brock, PhDLance Dalleck, PhDEric Goulet, PhDRobert Gotshall, PhDAlexander Hutchison, PhDM. Knight-Maloney, PhDLen Kravitz, PhDJames Laskin, PhDYit Aun Lim, PhDLonnie Lowery, PhDDerek Marks, PhDCristine Mermier, PhDRobert Robergs, PhDChantal Vella, PhDDale Wagner, PhDFrank Wyatt, PhDBen Zhou, PhD

Official Research Journal of the American Society of

Exercise Physiologists

ISSN 1097-9751

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

1Faculty 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 non-communicable 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

SubjectsThirty 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 MeasurementsWaist 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 CompositionBody 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 PressureTo 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 SEM-1, Japan).

Aerobic CapacityThe 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 (hp-cosmo 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 ProgramThe 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 self-paced 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 ChemistryAfter 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 HDL-Cholesterol 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 self-paced group (P<0.05).

Table 1. Baseline Characteristics of Study Groups.

VariableTotal

(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

Hip (cm) 104.9 ± 7.2 104.4 ± 9.5 105.3 ± 4.1

WHR .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

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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

LDL-C (mg·dL-1) 145.7 ± 40.6 147.5 ± 36.1 143.8 ± 45.8

HDL-C (mg·dL-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

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

Pre-training Post-Training t P-Value

VO2 peak (mL·kg-1·min-1)Speed walking 21.8 ± 2.9 25.2 ± 3.4** -6.730 .000

Self-Paced 22.9 ± 2.9 23.7 ± 3.2 -1.922 .075Weight (kg)

Speed walking 68.1 ± 10.9 67.9 ± 11.2 .703 .494Self-Paced 62.1 ± 4.3 61.4 ± 4.1 1.543 .145

BMI (kg·m-2)Speed walking 28.0 ± 3.6 27.9 ± 3.9 .940 .363

Self-Paced 25.6 ± 1.1 25.3 ± 1.3 1.546 .144Waist (cm)

Speed walking 89.4 ± 8.4 87.1 ± 6.2 2.088 .056

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Self-Paced 87.1 ± 3.5 86.4 ± 4.3 1.022 .324

Hip (cm)Speed walking 104.4 ± 9.5 102.9 ± 8.2 2.238 .052

Self-Paced 105.3 ± 4.0 104.5 ± 4.2 1.309 .212WHR

Speed walking .86 ± .06 .85 ± .05 1.182 .257Self-Paced .83 ± .04 .83 ± .04 .186 .855

%Body FatSpeed walking 35.9 ± 4.3 35.4 ± 3.5 .897 .385

Self-Paced 34.7 ± 2.8 34.0 ± 4.1 1.138 .274Resting HR (beats·min-1)

Speed walking 87.5 ± 8.7 80.8 ± 8.7** 3.790 .002Self-Paced 82.8 ± 6.5 76.4 ± 5.7** 4.326 .001

Resting SBP (mmHg)Speed walking 128.7 ± 14.1 121.5 ± 13.7 1.935 .073

Self-Paced 133.6 ± 10.8 127.3 ± 8.3** 3.201 .006Resting DBP (mmHg)

Speed walking 76.8 ± 6.9 77.0 ± 6.8 -.097 .924Self-Paced 76.7 ± 9.2 73.5 ± 7.5* 2.567 .022

FBG (mg·dL-1)Speed walking 99.8 ± 9.2 96.7 ± 14.7 1.225 .241

Self-Paced 102.6 ± 18.4 102.5 ± 18.3 .127 .900TC (mg·dL-1)

Speed walking 237.1 ± 49.2 211.4 ± 33.7* 2.143 .050Self-Paced 225.1 ± 58.0 224.6 ± 62.4 .161 .874

TG (mg·dL-1)Speed walking 141.7 ± 52.9 115.1 ± 33.3* 2.474 .027

Self-Paced 116.1 ± 39.2 121.6 ± 36.2 -1.742 .103LDL-C (mg·dL-1)

Speed walking 147.5 ± 36.1 128.5 ± 30.4 1.592 .134Self-Paced 143.8 ± 45.8 144.1 ± 47.3 -.098 .923

HDL-C (mg·dL-1)Speed walking 58.8 ± 13.5 58.5 ± 13.9 .142 .889

Self-Paced 61.1 ± 8.0 60.9 ± 8.1 .356 .727TC/HDL-C

Speed walking 4.2 ± 1.2 3.8 ± 1.1 1.487 .159Self-Paced 3.8 ± 1.3 3.8 ± 1.5 -.225 .825

hs-CRP (mg·dL-1)Speed walking 2.8 ± 3.0 2.4 ± 1.9 .984 .342

Self-Paced 1.71 ± 1.4 1.5 ± 1.1 1.196 .252Values 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

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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 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.

VariablesSpeed

Walking Self-Paced t P-Value

VO2 peak (mL·kg-1·min-1) 3.4 ± 1.9** .80 ± 1.6 3.972 .000

Weight (kg) -.15 ± .85 -.68 ± 1.7 1.071 .297

BMI (kg·m-2) -.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

%Body Fat -.53 ± 2.3 -.71 ± 2.4 .208 .836

Resting HR (beats·min-1) -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

FBG (mg·dL-1) -3.1 ± 9.9 -.13 ± 4.1 -1.086 .287

TC (mg·dL-1) -25.7 ± 46.5* -.47 ± 11.2 -2.045 .050

TG (mg·dL-1) -26.6 ± 41.6** 5.5 ± 12.1 -2.863 .011

LDL-C (mg·dL-1) -19.0 ± 46.2 .33 ± 13.2 -1.558 .138

HDL-C (mg·dL-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

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 CapacityCardiorespiratory 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

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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 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 post-training (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 VO 2 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 VO 2 peak in the present study.

Walking on Resting Heart Rate and Blood PressureAfter 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

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(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 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 FactorsAfter 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.

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ACKNOWLEDGMENTSThe 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: tkritpet@yahoo.com

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