The 1-Mile Walk Test is a Valid Predictor of VO 2max. and is a Reliable Alternative Fitness Test to the 1.5-Mile Run in U.S.

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1 MILITARY MEDICINE, 176, 6:669, 2011 The 1-Mile Walk Test is a Valid Predictor of and is a Reliable Alternative Fitness Test to the 1.5-Mile Run in U.S. Air Force Males Laura Weiglein, MSEd * ; Jeffery Herrick, PhD * ; Stacie Kirk, PhD ; Erik P. Kirk, PhD * ABSTRACT The purpose of this study was to assess the validity of the 1-mile walk (Rockport Walk Test) as a predictor of and determine whether the 1-mile walk is a reliable alternative to the 1.5-mile run in moderately fit to highly fit U.S. Air Force males. Twenty-four (33.0 ± 1.5 years) males completed a maximal treadmill (50.3 ± 1.4 ml/ kg/min), 1-mile walk, and 1.5-mile run. For the 1-mile walk, there were no significant differences between measured and predicted ( p = 0.177, r = 0.817). There were no significant differences ( p = 0.573) between points scored in the Air Force Fitness Test for the 1-mile walk and 1.5-mile run tests. In conclusion, the 1-mile walk test is a valid predictor of and can be used as an alternative fitness test to the 1.5-mile run in assessing cardiovascular fitness in Air Force males. INTRODUCTION The United States Air Force has recognized the importance of physical fitness for mission readiness, health, and disease prevention since its inception in The Air Force Fitness Program is used to determine mission readiness and has greatly evolved over the past 6 decades with the most recent update effective July 2010 under Air Force Instruction (AFI) The Air Force Fitness Program includes a biannual fitness assessment consisting of the following components: 1.5-mile run (2.4 km), 1-minute push-ups, 1-minute sit-ups, and abdominal circumference measurement. As one change to the Air Force Fitness Program, the 1-mile (1609 m) walk test, also known as the Rockport Walk Test, was implemented as an alternative cardiovascular fitness test for injured Airmen who are medically exempt from running. 2,3 Despite the implementation of the 1-mile walk, it has yet to be validated in an Air Force population. The 1-mile walk test was developed by Kline et al. 3 to predict using a sample population of adults between 40 and 69 years. However, the validity of the Kline et al. 3 equation for predicting has not been validated in males under the age of 40 years, which represents the majority of Air Force personnel.4 In fact, Dolenger et al. 5 and George et al. 6 suggested that the 1-mile walk equation may overestimate in civilians under the age of 40 years by as much as 23%. The purpose of the Air Force Fitness Program is to ensure mission readiness; therefore, accurate fitness assessments are essential to meet this objective. The primary purpose of this study was to assess the validity of the 1-mile walk test as a predictor of aerobic capacity ( ) in active duty Air Force males. The secondary purpose of this study was to examine whether the 1-mile walk is a reliable alternative test for the 1.5-mile run. * Department of Kinesiology & Health Education, Southern Illinois University Edwardsville, Edwardsville, IL th Medical Group, 310 W. Losey Street, Scott AFB, IL Department of Special Education and Communication Disorders, Southern Illinois University Edwardsville, Edwardsville, IL METHODS Active duty Air Force males aged 18 to 44 years were recruited from Scott Air Force Base, IL, using nonprobability stratified sampling. Before data collection, subjects completed the Air Force Fitness Screening Questionnaire, obtained physician clearance, and signed informed consent documents approved by Southern Illinois University Edwardsville and Wright Patterson Air Force Base Medical Group Institutional Review Boards. Exclusion criteria included medical exemption from cardiovascular fitness testing, musculoskeletal injury, metabolic disorders, 2 or more risk factors for cardiovascular disease, tobacco usage, and use of medications that attenuate heart rate. Subjects completed 3 fitness assessments: 1-mile (1,609 m) walk, 1.5-mile (2.4 km) run, and treadmill. Tests were completed in a random counterbalanced order within 30 days with a minimum of 48 hours between tests. Subjects wore the Air Force physical training uniform consisting of shorts, T-shirt, and running shoes. Before each assessment, subjects avoided high intensity exercise for 48 hours and caffeine and dietary supplement consumption for 24 hours. Food consumption was avoided within 3 hours of testing. Height, weight, and body composition were measured on the date of the test. Body composition was assessed using dual energy X-ray absorptiometry ([DXA] Lunar DPX-IQ; Lunar Corporation, Madison, WI). Weight was measured using a digital scale accurate to ±0.1 kg (Model #PS6600; Befour Inc., Saukville, WI), and height was measured using a stadiometer (Model 226, Hite-Rite Precision Mechanical Stadiometer; SECA, United Kingdom) mile Run & 1-mile Walk The 1-mile walk and 1.5-mile run were completed at the Scott AFB outdoor quarter-mile ( m) track. The objective of the 1.5-mile run was to run the distance as fast as possible. During the 1-mile walk, participants wore Polar FS2C heart rate monitors (Polar Inc., Westbury, NY ) and walked as quickly as possible while keeping 1 foot in contact with MILITARY MEDICINE, Vol. 176, June

2 the ground. Final heart rate, walk time, body weight, age, and sex were entered into the equation of Kline et al. 3 to predict. Predicted and 1.5-mile run time were compared against Air Force standards by age and gender to determine points scored on the Air Force Fitness Test. 2 Treadmill Test assessments were completed using a motor driven treadmill with expired gases measured by standard indirect calorimetry (TrueOne 2400; ParvoMedics, Sandy, UT). Subjects ran at a constant self-selected speed ( mph) with an increase in grade by 2.5% every 2 minutes until maximal exertion. Heart rate, blood pressure, and rate of perceived exertion were measured at the end of each stage. was determined as the highest measured value at the completion of the assessment. Maximum oxygen consumption was reached when at least 2 of the following criteria were met: (1) Oxygen consumption plateau despite increase in workload; (2) Maximum heart rate within 15 beats per minute of the age-predicted heart rate maximum (220 age); (3) rate of perceived exertion greater than 17; and (4) respiratory exchange ratio greater than ,5 8 One participant failed to achieve maximum exertion and was excluded from data analysis. Additionally, researchers adhered to the relative and absolute indications of the American College of Sports Medicine (ACSM) to terminate exercise testing. 9 Statistical Analysis In accordance with the Air Force Fitness Test, predicted from the 1-mile walk was calculated using the Kline et al. 3 regression equation: = ( WT ) ( AGE ) + (6.315 SEX ) ( TIME ) ( HR ), where WT = Weight (lb); SEX = Males, 1and Females, 0; TIME = walk time (minute); and HR = final heart rate (bpm). Statistical analyses were completed using PASW Statistics 18 (SPSS Inc., Chicago, IL). A paired samples t -test and Pearson product-moment correlation were performed to compare measured and 1-mile walk predicted (α = 0.05). The percentage of participants with predicted within ±4.5 ml/kg/min of the measured was computed to allow comparison between other similar studies. 5,6,10,11 A Pearson product moment correlation was also calculated to compare 1.5-mile run time to measured. A paired samples t -test and regression analysis was performed to compare differences between means of points scored from the 1.5- mile run time and 1-mile walk predicted as defined by the Air Force Fitness Program. 2 Air Force Fitness Test scores from the 1.5-mile run and 1-mile walk were compared against the ACSM percentile rankings for cardiovascular fitness. 9 RESULTS Twenty-four subjects ( N = 24, 8 officers and 16 enlisted) completed the entire protocol and met the criterion for. This distribution between officers and enlisted participants is similar to the male active duty Air Force population and thus allows for generalization to the population. 4 Descriptive data are shown in Table I. There were no significant differences between measured and predicted using the 1-mile walk equation ( p = 0.177) of Kline et al. 3. Mean residuals between predicted and measured were 1.14 ml/kg/min, and Pearson s product moment correlations were high (r = 0.817; Fig. 1 ). Interestingly, 79% of participants had predicted within ±4.5 ml/kg/ min of measured ; statistical analysis comparing this study to similar studies assessing the validity of the 1-mile walk can be found in Table II. Additionally, 1.5-mile run time and measured produced a high negative correlation (r = 0.890; Fig. 2 ). As defined by the Air Force Fitness Program, a point value on a scale of 0 to 60 is assigned to the outcomes of the 1-mile walk (predicted ) and 1.5-mile run (time) based on age and sex. 2 Table III shows a sample of the scoring for the 2 cardiovascular fitness tests for 1 age group. 2 Results indicate there were no significant differences between points scored on the 1-mile walk and 1.5-mile run, and high correlation between the tests were also found ( p = 0.573, r = 0.827, Fig. 3 ). To further compare the relationship between points scored on the Air Force Fitness Test for the 2 tests, we analyzed results from the 1.5-mile run and 1-mile walk against ACSM percentile rankings. A high correlation ( r = 0.975) was found TABLE I. Descriptive Data Mean ± SEM Min Max Age (years) 33.0 ± Body Mass Index (kg/m 2 ) 25.8 ± Body Fat (%) 23.9 ± Fat Mass (kg) 19.6 ± Fat Free Mass (kg) 60.8 ± Measured (ml/kg/min) 50.3 ± Predicted (ml/kg/minute) 49.2 ± mile Run Time 10:45 ± 0:18 7:54 13:33 Values are means ± standard error of mean. FIGURE 1. Scatter plot of measured vs. predicted (ml/kg/ min) using the 1-mile walk test by Kline et al. (1987). 670 MILITARY MEDICINE, Vol. 176, June 2011

3 TABLE II. Analysis of Validity of 1-mile Walk in Males Observed Predicted Residual r R2 % Current Study % 79.0 Kline et al. (1987) % NA Dolenger et al. (1994) % 28.0 George et al. (1998) % 63.9, maximal oxygen consumption expressed in ml/kg/min; %, percentage of participants with measured and predicted that fall ± 4.5 ml/kg/min. FIGURE 2. Scatter plot of (ml/kg/min) vs. 1.5-mile run time (min). FIGURE 3. Scatter plot of points scored on the Air Force fitness test from the 1-mile walk and 1.5-mile run on scale of 0 to 60 points. TABLE III. Air Force Fitness Test Scoring for 1.5-mile Run and One-mile Walk in Males 30 to 39 years of age Run Time (minute:second) Points 1-Mmile Walk( ) 9: :35 9: :59 10: :11 10: :24 10: :38 10: :52 11: :07 11: :23 11: :39 11: :57 12: :15 12: :34 12: :54 13: :15 13: :37 14: FIGURE 4. Scatter plot of points scored on the Air Force 1.5-mile run (0 60 points) vs. ACSM percentile ranking for 1.5-mile run based on age and sex. Score chart reproduced from AFI Score chart. Each 10-year age group for both genders can be found in AFI between points scored on the 1.5-mile run and ACSM percentile rankings ( Fig. 4 ). Only a moderate correlation ( r = 0.674) was found between points scored on the 1-mile walk compared to ACSM rankings ( Fig. 5 ). DISCUSSION Results of this study indicate that the 1-mile walk using the equation of Kline et al. 3 is a valid predictor of in active duty Air Force males. To our knowledge, the 1-mile walk has not previously been validated in a military population, and FIGURE 5. Scatter plot of points scored on the Air Force 1-mile walk (0 60 points) vs. ACSM percentile ranking for 1.5-mile run based on age and sex. previous studies were inconclusive as to whether this assessment was valid in other young adult populations. Dolenger et al. 5 and George et al. 6 reported significant overestimation of in college populations. In contrast, MILITARY MEDICINE, Vol. 176, June

4 McSwegin et al. 10 and Greenhalgh et al. 11 concluded that the 1-mile walk is a valid predictor of in high school and college students. Greenhalgh et al. 11 suggested the overprediction of by Dolenger et al. 4 and George et al. 5 was likely due to using sample populations with lower fitness levels. Although the mean age of subjects in this study is greater than that in previous studies, the current sample population has an overall higher fitness level with a mean of ± 6.96 ml/kg/min. When developing the prediction equation, Kline et al. 3 used a fit sample relative to age. In that study, the mean age of males was 46.6 ± 10.7 years with a mean of 42.2 ± 9.8 ml/kg/ min. Use of a fit population relative to age may explain the validation of the 1-mile walk in physically fit populations of different ages. Based on results of this study, age does not appear to affect the validity of the 1-mile walk in highly fit populations. Therefore, our findings support the Greenhalgh et al. 11 conclusion that the 1-mile walk is valid in highly fit populations. The secondary purpose of this study was to examine whether the 1-mile walk is a reliable alternative test for the 1.5-mile run. The Air Force Fitness Test allocates a point value on a 0 to 60 scale for results of the 1.5-mile run and 1-mile walk based on age and sex. 2 The high correlation and lack of significant differences between point values indicate that participants earned equivalent points on the 2 tests; therefore, our results suggest the 1-mile walk is reliable alternative to the 1.5-mile run in moderate to highly fit Air Force males. Although the only Airmen assigned to the 1-mile walk are those medically exempt from running, determining that there are no significant differences between points scored in moderate to highly fit Airmen ensures the Air Force consistently assesses cardiovascular fitness, regardless of injury status. Furthermore, because military members do not have an option for which test to complete, there is no unfair advantage for Airmen being assigned to one test over another. Therefore, based on results of this study, the 1-mile walk and 1.5-mile run can be used interchangeably resulting in similar outcomes. Despite our findings that equivalent scores were found between the 2 tests, Figure 3 suggests that subjects with lower fitness scores were more likely to score higher on the 1-mile walk than on the 1.5-mile run. A comparison of Figures 4 and 5 further emphasizes this theory. Figure 4 shows a linear relationship between Air Force Fitness Test scores from the 1.5-mile run compared to ACSM percentile rankings. In contrast, the large variance between 1-mile walk scores and ACSM rankings is skewed to the right in Figure 5, indicating that individuals with lower fitness levels were awarded high scorer on the Air Force Fitness Test for the 1-mile walk. Taken together, it appears that Airmen with lower levels of fitness may score higher on the 1-mile walk than the 1.5-mile run, leading to an overestimation of cardiovascular fitness. Our sample did not include subjects in the lowest 40% based on ACSM normative values to statistically assess this observation that those of lower fitness levels may score higher on the 1-mile walk than the 1.5-mile run. However, this study was aimed toward assessing the 1-mile walk in a sample population that would generalize to a majority of the Air Force male population. With a mean of ± 6.96 ml/ kg/min, the cardiovascular fitness level of our sample population was consistent with other military fitness studies. In one study of Air Force males, runners had a mean of 62.2 ± 4.9 ml/kg/min. 12 Willford et al. 8 reported a mean of 47.9 ± 10.3 ml/kg/min in male Air Force officers. Similarly, Mello et al. found a mean of 50.4 ± 7.7 ml/ kg/min in male Army soldiers. 13 Therefore, we can conclude that the results from this study can generalize into the majority of the Air Force males; however, further investigation is necessary to ensure those of low levels of fitness are accurately being assessed for mission readiness. Previous studies have identified that low levels of fitness are highly correlated to incidence of overuse injuries in military personnel. 14,15 Therefore, Airmen with low fitness levels are more likely to sustain injury that would lead to medical exemption from running and assignment to the 1-mile walk. This emphasizes the need to further investigate the 1-mile walk in low fit Airmen because a large percentage of those assigned to the 1-mile walk are likely to have lower fitness levels. Because the purpose of the Air Force Fitness Program is to assess mission readiness, a potentially skewed allocation of points in Airmen of lower fitness would not allow the Air Force to accurately assess mission readiness. Therefore, further research is warranted for assessing the 1-mile walk as a reliable alternative test to the 1.5-mile run in Airmen below the 40% by ACSM criteria. One limitation is that this study only included males; however, this population was selected since males aged 18 to 44 years make up approximately 75% of the Air Force population. 4 Previous literature using mixed-gender samples validated use of the 1-mile walk in highly fit men and women; therefore, this indicates our result can likely generalize into Air Force females. Another limitation is that we were not able to break out results by 10-year age groups defined in the Air Force Fitness Program because of the small sample size. 2 Despite limitations, this study provides preliminary research into the validity of the 1-mile walk in an Air Force population. In conclusion, this study indicates the 1-mile walk using the equation of Kline et al. 3 is a valid predictor of in active duty Air Force males. Additionally, the 1-mile walk was found to be a reliable alternative cardiovascular fitness test to the 1.5-mile run in moderate to high fit Airmen; therefore, a majority of Airmen can expect to earn equivalent scores, regardless which cardiovascular fitness test the military member is assigned. However, further research is warranted to compare point values on the 1-mile walk and 1.5-mile run in Airmen under the 40% by ACSM rankings to ensure consistent assessment of mission readiness of all Airmen. ACKNOWLEDGMENTS We thank the participants who volunteered their time and effort for this study. Additionally, we thank Austin Rabbitt and the staff of the Exercise Physiology 672 MILITARY MEDICINE, Vol. 176, June 2011

5 Labfor their time and expertise. Finally, we thank Lt Col Alice Chapman, the Scott AFB Health and Wellness Center, and the 375th Medical Group for assistance and support. This project was supported by an internal grant at Southern Illinois University Edwardsville as part of the Research Grants for Graduate Students Program. REFERENCES 1. Constable, Palmer, B : The Process of Physical Fitness Standards Development. Report No. HSIAC-SOAR Wright-Patterson Air Force Base, Human Systems Information Analysis Center, Available at Location=U2&doc=GetTRDoc.pdf ; accessed July 27, Department of the Air Force : Fitness Program (Air Force Instruction ). Secretary of the Air Force, Available at ing.af.mil. 3. Kline GM, Porcari JP, Hintermeister R, et al : Estimation of VO 2max from a one-mile track walk, gender, age, and body weight. Med Sci Sports Exerc 1987 ; 19 (3) : Air Force Personnel Center : Interactive Demographic Analysis System [Data file], Available at broker8.exe?_program=ideas.ideas_default.sas&_ service=prod2pool3&_debug=0 ; accessed July 15, Dolenger FA, Hensley LD, Marsh JJ, Fjelstul JK : Validation of the Rockport fitness walking test in college males and females. Res Q Exerc Sport 1994 ; 65 (2) : George JD, Fellingham GW, Fisher AG : A modified version of the Rockport fitness walking test for college men and women. Res Q Exerc Sport 1998 ; 69 (2) : Castero-Piñero J, Mora J, Gonzalez-Montesinos JL, Sjöström M, Ruiz JR : Criterion-related validity of the one-mile run/walk test in children aged J Sports Sci 2009 ; 27 (4) : Williford HN, Olsen MS, Sport K, Blessing D, Wang N : The prediction of fitness levels of United States Air Force officers: Validation of cycle ergometry. Mil Med 1993 ; 159 (3) : Thompson WR, Gordon NF, Pescatello LS (editors): ACSM s Guidelines for Exercise Testing and Prescription, Ed 8, pp 119. Philadelphia, Lippincott Williams, & Wilkins, McSwegin PJ, Plowman SA, Wolff GM, Guttenberg GL : The validity of a one-mile walk test for high school age individuals. Meas Phys Educ Exerc Sci 1998 ; 2 (1) : Greenhalgh HA, George JD, Hager RL : Cross-validation of a quartermile walk test using two regression models. Meas Phys Educ Exerc Sci 2001 ; 5 (3) : Hartung GH, Krock LP, Crandall CG, Bisson RU, Myhre LG : Prediction of maximal oxygen uptake from sub-maximal exercise testing in aerobically fit and nonfit men. Aviat Space Env Med 1993 ; 64: Mello RP, Murphy MM, Vogel JA : Relationship between a two mile run for time and maximal oxygen uptake. J Appl Sports Sci Res 1988 ; 2 (1) : Knapik J, Ang P, Reynolds K, Jones B : Physical fitness, age, and injury incidence in infantry soldiers. J Occup Med 1993 ; 35 (6) : Rosendal L, Langberg H, Skov-Jensen A, Kjaer M : Incidence of injury and physical performance adaptations during military training. Clin J Sport Med 2003 ; 13 (3) : MILITARY MEDICINE, Vol. 176, June