Comparison of Energy Expenditure to Walk or Run a Mile in... : The Journal of Strength & Conditioning Research (original) (raw)
Introduction
A recent Trust for America's Health/Robert Wood Johnson 2009 report noted obesity rates increased in 23 states over the past year with no states reporting any decline (21).
Mississippi continues with the highest percentage of obese adults (32.5%) in the United States. Moreover, Ogden et al. (18) in a Center for Disease Control report noted that obesity continues as a major health problem as body mass index has significantly increased over the last 30 years. Health-related morbidities of obesity include hypertension, insulin resistance, coronary heart disease, dyslipidemia, type 2 diabetes, gallbladder disease, and some forms of cancer (17,20). As a goal, The Healthy People 2010 objective includes an obesity prevalence <15% in men and women (18).
An abundance of research over the past 30 years has found that as physical activity increases, all-cause mortality decreases (11,14,19). Walking or running is an excellent activity to increase energy expenditure, thus positively influencing health. Haskell et al. (8) in an American College of Sports Medicine position paper, recommended walking briskly twice per week and jogging twice per week as an example of meeting the physical activity weekly guidelines. Also, Manson et al. (14) found walking as effective as vigorous exercise in cardiovascular risk reduction in a large group (>73,000) of women aged 50 to 79 years.
Researchers have investigated the energy cost of walking and running a given distance in normal weight adults (7,9,16). In general, the energy cost is higher when running a given distance such as a mile compared with walking the same distance (7,9,16). However, Kram and Taylor (10) found the cost of running a fast or slow mile similar in quadrupeds that ranged in size from 32 g to 141 kg. Moreover, limited research has compared the energetic cost of overweight with normal weight adults during walking (3,4). In our literature review, we were unable to locate any studies that included overweight men and women as a group when examining the energy expenditure to walk or run a mile. Consequently, comparing overweight men and women with normal weight adults is a unique aspect of this study. The purpose of this investigation was to compare energy expenditure (caloric cost) in walking and running in normal weight and overweight adult men and women. The data sets for this study were derived from other studies from our laboratory (12,22).
Methods
Experimental Approach to the Problem
Indirect calorimetry was used to examine energy expenditure during treadmill walking or running with the caloric values corrected to a mile distance. Energy expenditure was compared in absolute units (kilocalories) and kilocalories relative to mass or fat-free body mass. Finally, a regression equation was developed to predict the energy expenditure to walk or run a mile.
Subjects
A total of 50 subjects participated. Thirty participants were recruited from the University of Mississippi and Oxford, Mississippi community with 20 subjects (marathon runners [MR]) from Baton Rouge and New Orleans, LA. Twenty-three of the participants were men and 27 women. The normal weight walkers (NWW) consisted of 11 men and 8 women, overweight walkers (OW) 2 men and 9 women, and the MR 10 men and 10 women. The study was approved by the committee for the use of human subjects at the University of Mississippi (NW and OW) and the University of New Orleans (MR), and each participant signed an informed consent. Some of the data from the MR group have been previously published (12,13).
Procedures
All subjects completed body composition testing via dual-energy x-ray absorptiometry. Normal weight walkers and OW were tested on a Hologic Delphi, QDR series (Bedford, MA, USA) apparatus, whereas the MR completed testing on a Lunar/GE DPX-NT (Madison, WI, USA) apparatus. The NWW and OW walked on the treadmill at 3 different walking speeds (preferred, 25% below, and 25% above preferred). After a brief warm-up, the subjects walked for 5 minutes at the 3 speeds. Preferred walking speed was determined from 6 timed 50-feet trials. Only the preferred walking speed is reported in this article. The MR group completed a 1-hour treadmill run at their most recent marathon pace. Metabolic data (oxygen uptake, carbon dioxide production, and pulmonary ventilation) were measured in all NWW and OW subjects with a ParvoMedics TrueOne 2400 (Sandy, UT, USA) metabolic measurement system. In the MR group, some of the subjects were tested via a Sensormedics (Model 2900c, Anaheim, CA, USA) system (n = 15) or with the ParvoMedics TrueOne 2400 employed to test the remaining subjects. Before all metabolic testing, the apparatus was calibrated against standard gases (O2 = 16%, CO2 = 4.00%).
Oxygen uptake and respiratory exchange ratio values were used to calculate energy expenditure (kilocalories). To compare energy expenditure under walking and running conditions, kilocalories was expressed per mile. Physical activity was estimated after Sallis et al. (23). Normal weight walkers and OW completed the recall questionnaire with MR values extrapolated from a 3-month running recall. Because only very hard activities (>7.0 METS) were recorded for MR, only these activities were compared across groups.
Statistical Analyses
Analysis of variance (ANOVA) was used for overall significance with Scheffe post hoc analysis employed to examine group comparisons. Specifically, a 1-way ANOVA was used to compare energy expenditure across groups, and a 2-way ANOVA was employed to compare energy expenditure of groups by gender. Also, multiple regression (forward selection) analysis was used to predict caloric expenditure. Statistical significance was set at the 0.05 level.
Results
In Table 1, physical characteristics are presented. As expected, significant differences in body composition were noted with OW exhibiting higher body mass and relative fat. The runners were significantly older than the walkers. Physical activity (hours per week > 7.0 Mets) was significantly higher in MR (3.1 ± 3.6) when compared with NWW (2.2 ± 4.2) or OW (0.6 ± 1.2) with no differences noted between NWW and OW.
Physical characteristics.*†
Table 2 includes energy expenditure across groups for walking or running a mile at preferred speed (walkers) and recent marathon run pace (runners). As noted, gross caloric expenditure was similar across groups. However, MR expended more kilocalories per mile than NWW and OW when kilocalories was expressed relative to mass. Also, NWW expended more kilocalories per kilogram mass than OW. When kilocalories per kilogram fat-free weight (FFW) was compared, no differences occurred across groups.
Energy expenditure walking or running a mile in NWW, OW, and MR and physical activity recall.†
Gender differences in NWW and MR can be found in Table 3. Overweight walkers were not included in this analysis as only 2 men were included in this group. An overall main effect gender difference was found when NWW and MR were compared; however, the interaction of group by gender was not significant. When energy expenditure was expressed per kilogram of mass or fat-free body mass, no gender differences were noted.
Energy expenditure walking or running a mile by gender in the NWW and MR.†
The Figure shows a scatterplot of mass and energy expenditure to run or walk a mile irrespective of groups. The correlation was r = 0.769 (_r_2 = 0.591) and was improved significantly (p < 0.05) with the addition of gender in a multiple regression model (R = 0.795, _R_2 = 0.632). Predicting energy expenditure (kilocalories) to walk or run a mile yielded the following equation:
Scatterplot of mass (kilograms) and energy expenditure (kilocalories) to walk or run 1 mile (r = 0.769).
Discussion
A unique aspect of this study was to include an overweight adult group as previous work has focused on apparently healthy normal weight adults (2,7,9,16). Obesity is an important topic to study because about a third of the U.S. population is overweight. The relative body fat (37.5%) of the overweight men and women in this study would place the group in about the third percentile (1st to 10th percentile range) based on age and gender according to data published in the American College of Sports Medicine's recent guidelines for exercise testing and prescription text (1). In comparison, NWW averaged about the 31st and MR the 63rd percentile.
To compare walking and running energy expenditure, it was necessary to report the data per a common distance such as a mile or kilometer. Our results revealed that total energy expenditure for the mile yielded similar absolute caloric values during walking or running at preferred pace. Hall et al. (7) recently reported that running yielded higher values than walking a distance of 1,600 m. In their study, all participants completed both running and walking trials. Miller and Stamford (16) observed that absolute energy expenditure while walking at 2.0 or 4.0 mph with added hand and ankle weights (9.0 kg added weight) yielded higher values than running at 5.0 to 7.0 mph without added weight. Mayhew et al. (15) found untrained men to expend more kilocalories than trained men or women (trained and untrained) when the energy expenditure was expressed per kilometer. The untrained men weighed 10.6 kg more than the trained men. Cureton and Sparling (5) examined the effect of added weight on distance run performance. Extrapolation of data provided from Cureton and Sparling's Table 3 reveals that running a mile at 188 meters per minute (7.0 mph) with an added 7.5% weight increased the energy expenditure from 111.3 to 118.6 kcal in the participants (men). The added weight averaged 5.3 kg across the 10 subjects. Consequently, added body weight yield (actual or artificially added) leads to increased energy expenditure for running (or walking) performance.
When the energy expenditure data were compared relative to mass (kcal·mile−1·kg BW−1), a different pattern emerged as all groups were significantly different from one another. MR expended the most kilocalories per kilogram of mass per mile with the overweight men and women walkers the least (Table 2). Expressing the data per kilogram of mass revealed a blunting effect of the additional mass in the overweight men and women as this group expended 10% less kilocalories per kilogram of mass per mile than the NWW and 14% less than the MR. The overweight men and women had an additional 15.0-18.7 greater fat mass values than the NWW or MR. Because fat-free mass was similar across groups (Table 1), the excess mass was primarily adipose tissue. These results demonstrate the metabolic effect of transporting excess mass during a weight bearing activity such as walking, that is, it lowers the energy expenditure per mile per kilogram of mass. Expressing energy expenditure per kilogram of fat-free mass (kcal·mile−1·kg FFW−1) yielded similar values across groups. Hall et al. (7) observed that running yielded a significantly higher value than walking in participants who completed both running and walking trials.
As noted in Table 3, the male participants expended more kilocalories for completing the mile run or walk than the females. When the data were expressed relative to mass or fat-free mass, no differences were noted. A comparison of gender differences in the gross caloric expenditure for a given distance has yielded mixed results with some studies showing no differences (2) and others showing higher values in men (6) or women (9). Loftin et al. (12) found male MR to expend more kilocalories than females during a 1-hour run at marathon pace and corrected to the most recent marathon time. However, gender effect disappeared when the caloric value was expressed per kilogram of mass per kilometer and when expressed kcal·kg FFW−1·km−1. Hall et al. (7) also observed no gender difference when the data were expressed kcal·kg FFW−1·km−1 for running or walking a distance of 1,600 m.
In the regression equation predicting the energy expenditure to run or walk a mile, mass accounted for 59.1% of the variance with gender adding another 4.1%. From a practical perspective, this equation can be used to predict walking or running a mile, although we caution that the equation has not been cross validated. As noted in Table 2, walking for an hour at preferred pace would result in NWW and OW completing about 3 miles with MR completing about 6.8 miles. A woman with a mass of 80 kg would expend about 294 kilocalories per hour, whereas a woman running (mass of 70 kg) would expend about 617 kilocalories per hour. Running for an hour at marathon pace (Table 2) yields a little over twice the energy expenditure than walking at about 3 mph. However, according to the most recent American College of Sports Medicine/American Heart Association guidelines for physical activity and public health (8), walking at 3.0 mph for an hour would be sufficient for one day of physical activity.
Before beginning an exercise program, overweight individuals with additional cardiovascular disease risk factors should seek physician approval to screen for underlying cardiovascular and musculoskeletal disorders (17,20). For example, overweight adults are at a higher risk for developing osteoarthritis, and Syed and Davis (24) noted that women may be at higher risk than men because of lower lean mass that may increase quadriceps fatigue.
In conclusion, our data indicate that the overweight adults of this study expended similar absolute gross kilocalories per mile or kilocalories relative to fat-free body mass as NWW or MR at preferred walking or running pace. A different pattern emerged when the energy expenditure was expressed relative to mass with the MR expend the most and OW the least kilocalories. In a regression model, mass accounted for the greatest proportion of energy expenditure variance with gender also as a significant contributor. Finally, including an equation to predict energy expenditure (kilocalories) per mile is useful for exercise prescription as most equations only predict energy expenditure per minute.
Practical Applications
Energy expenditure expressed as kilocalories increases as mass increases for physical activities such as walking or running where the body is supported wholly by the musculoskeletal system. Our results yielded similar gross energy expenditure for walking or running a mile. We provide a regression equation (kcal = mass (kg) × 0.789 − gender (men = 1, women = 2) × 7.634 + 51.109) that the practitioner can readily apply in a field-based setting. Walking may be an excellent physical activity in regard to caloric expenditure for overweight individuals that can physically tolerate this activity. Walking will typically require a longer time frame to complete a given distance when compared with running. We encourage walking as a planned physical activity in addition to including walking as part of normal daily life.
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Keywords:
energy expenditure; running; walking
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