ASSESSING FIREFIGHTER AEROBIC CAPACITY: THE ROCKPORT FIELD TEST
BY JOHN LECUYER
In August 1997, the 14th International Association of Fire Fighter (IAFF) Redmond Symposium was held in Toronto, Canada. The Symposium introduced the end-product of the Fire Service Joint Labor/Management Wellness Fitness Initiative, a physical fitness and wellness program package. The package included a program manual covering medical evaluations, fitness, rehabilitation, and behavioral health and data collection. The physical fitness chapter identifies the components of fitness and includes fitness evaluation methods with several options for the cardiorespiratory component. The test protocols for each method are referenced in an appendix. This article presents an alternative mode of testing for the aerobic dimension not included in the manual–the Rockport one-mile walking test.
AEROBIC CAPACITY
Aerobic capacity refers to the body`s ability to take in, transport, and use oxygen. The maximal value is expressed as VO2max and reported in liters per minute (L/min-aerobic capacity) or, relative to body weight, in milliliters per kilogram of body weight per minute (ml/kg/min-aerobic power). The direct measure of VO2max involves the use of a treadmill or cycle ergometer and sophisticated equipment to measure respiratory gases. The process is time-consuming, expensive, and impractical for routine fitness program usage, particularly when a large number of people are to be tested. Therefore, alternatives have been developed that can estimate aerobic capacity from submaximal field test protocols. The field tests are validated back to the max test through statistical correlation.
The IAFF manual provided four field test methods: treadmill, stair machine, stationary cycle, and step test. Each type of test has advantages and disadvantages with regard to ease of administration, economy (cost of equipment), and the ability to accurately predict VO2. The limitation of the first three methods is that only one person can be tested at a time. The last method, the step test, is the only alternative that can accommodate multiple subjects. The choice of test is a matter of personal preference; all will serve the intended purpose and yield a VO2 score. I am convinced, however, that the Rockport one-mile walking test provides the most accurate, inexpensive alternative for field testing multiple subjects.
THE ROCKPORT WALKING TEST
The Rockport one-mile walking test was developed at the University of Massachusetts Medical School and funded by the Rockport Walking Institute in Marlboro, Massachusetts. The Institute commissioned the medical school to develop an alternative field test to estimate maximal oxygen consumption (VO2max) using a one-mile walk. Over a period of 18 months, 343 healthy adults (165 males, 178 females) in an age range between 30 and 69 years were evaluated. The investigation generated six equations for estimating the VO2max from the one-mile walk. The accuracy of the equations was similar, and the correlation between the direct measurement of VO2max using a treadmill protocol and the one-mile walk test was r = .93 (aerobic capacity expressed as L/pm), indicating an accurate test for an individual`s aerobic capacity.1
FIREFIGHTER STUDY
In an effort to evaluate the effectiveness of using the one-mile walk to assess the aerobic capacity of firefighters, I proposed and conducted the study with the assistance of Dr. Art Dickinson, Chief Bill Work of the Westminster (CO) Fire Department, and Chief Dick Spencer of the West Metro (CO) Fire Protection District, and in cooperation with the University of Colorado at Boulder. This study deviates from the original conducted by Kline in the following ways:
The firefighters in one group (A) were instructed to walk as fast as possible, per Kline. The second group (B) was instructed to walk briskly but not necessarily as fast as they could. Emphasis was placed on performing four even laps.
Purpose: To test the theory deduced from the case study that variable paces can estimate the VO2max accurately, two groups were used. One was instructed to walk “as fast as possible,” the other to walk briskly–not necessarily fast.
The best equation (aerobic capacity) reported by Kline and presented in the article abstract was not used in this study. An optional equation (aerobic power) provided by Dr. Ann Ward, one of the original investigators, with a lower correlation (r = .88) than the “best equation” (r = .93) was selected.
Purpose: To evaluate one alternative formula with a career firefighter population.
The firefighters performed only one trial vs. the two or more performed in the original study.
Purpose: In actual field use, only one attempt would be allowed for practical purposes.
A case study was added using one volunteer performing eight walk tests at varying paces over a period of one week.
Purpose: To assess the accuracy of the formula based on the theory that varying walk paces would produce heart rate adjustments that would preserve the accuracy of the equation.
SUBJECTS
Eighteen Colorado career firefighters from the Westminster (12) and West Metro (6) fire departments volunteered to participate in the study. Prior to participating, each firefighter`s age, weight, and vitals were recorded, in addition to a health risk appraisal and activity index.
TEST PROCEDURES
Treadmill test. Each firefighter performed a treadmill test at the University of Colorado Human Performance Laboratory to determine VO2max. The following protocol was used:
–A warm-up period (HR: 98 to 120 bpm) was conducted for a minimum of four minutes at a 0 percent grade with treadmill speed judged by activity history and heart-rate response to walking speed.
–If the firefighter appeared average or above in work capacity based on warm-up heart rate and what a firefighter should be able to perform for a minimum of six minutes and a maximum of 12 to 14 minutes, the grade was started at 5 percent. If the firefighter appeared below average in work capacity, the test was started at 0 percent grade. The treadmill grade was raised 2.5 percent every two minutes until the firefighter reached volitional maximum.
–The firefighter was encouraged to “go all out” and challenge the test. If a firefighter reached a 15 percent grade and completed the stage, the treadmill grade was lowered to 10 percent, and the firefighter was allowed to run at a comfortable speed of six to eight miles per hour.
–Metabolic measurements were taken every 20 seconds, the heart rate every 60 seconds, and a blood pressure reading every two minutes.
Walk test. The walk test was performed on two separate days (one for each department) on a standard quarter-mile track. Each firefighter performed only one test trial. The original study required each subject to perform a minimum of two trials to account for possible learning effects. The results revealed that one trial was sufficient to produce an accurate estimation of VO2max. Since repeated trials would reduce the utility of the test, a single trial was performed in this study.
Protocol
The test protocol was as follows and is as it appears in “The Rockport Guide to Fitness Walking.”2
Walk one-mile as fast as you can. Stretch for five to 10 minutes before and after. Wear good walking shoes and loose-fitting clothes. Maintain a steady pace.
Record your time to the nearest second. Most people walk between three and six miles per hour, so it should take 10 to 20 minutes to walk the mile.
Record your heart rate immediately at the end of the mile (it begins to slow almost immediately after you stop). Count your pulse for 15 seconds and multiply by four, then record this number. This gives you your heart rate per minute after your walk test.
Group A was instructed to walk “as fast as possible”; Group B was told to walk “briskly, but not necessarily as fast as possible.” Emphasis was placed on maintaining even laps. Each firefighter was equipped with a Polar heart rate monitor, and the heart rate was recorded immediately on completion of the fourth lap. The total walk time was also recorded on completion. The firefighter`s age, body weight, walk ending-heart rate, and walk time were logged and entered into the formula for calculation of VO2max. The formula selected was as follows:
(.0769 2 BWT) ` (.3877 2 AGE) ` (3.2649 2 TIME) ` (.1565 2 HR) 2 132.853 (` 6.315 male only) = VO2max ml/kg/min
BWT= body weight in pounds
HR = beats per minute
TIME = one-mile walk time (convert the seconds to decimals); a 12:15 time would be expressed as 12.25, a 12:30 time as 12.50, and so on.
AGE = age in years.
RESULTS
The correlation between actual VO2 (treadmill) and estimated VO2 (walk) for group A was r = .88, which is identical to the correlation found using this formula in the original study. The correlation for group B was r = .62, considerably lower than for group A. The poorer correlation for this group can be attributed to the fact that it was a smaller group (n = 6) and test times were slower, which for two members represented only 20 and 30 percent of their VO2max, an intensity well below the minimum threshold for an accurate estimation (see case study below).
CASE STUDY
A case study was conducted to evaluate the potential of identifying a submaximal pace that could determine aerobic capacity with accuracy. One 50-year-old career firefighter of average aerobic capacity volunteered to perform a series of one-mile walk tests over a period of seven days. During the test trials, heart rate and time were recorded for each lap–four pairs for each one-mile walk test. Of the eight test trials, two were thrown out as a result of duplicate or near duplicate times with other trials. This case study poses two questions:
1. Can varying paces in lieu of a maximal effort produce an accurate score?
2. If so, is there an accurate submaximal effort that falls within the American College of Sports Medicine (ACSM) guidelines of 40 to 60 percent of VO2max, thereby providing the option of testing higher-risk individuals without physician clearance?
Question 1
The walk test protocol instructs the subject to walk as fast as possible. The firefighter in this case study was instructed to walk slowly on the first walk test and to increase his pace for each subsequent test until his maximal speed was attained. The reason for the varying pace was to identify the range of paces and intensity of effort that are possible without affecting the accuracy of the equation. Typically, a few firefighters will not put forth their best effort. If lower intensity levels can produce an accurate estimation, retesting the less motivated may not be necessary.
Question 2
If lower intensities can produce an accurate estimation, then higher-risk individuals who would normally require a medical exam prior to testing could be safely evaluated without a pretest exam. “It is unnecessary for asymptomatic apparently healthy men and women, irrespective of their age or CAD [coronary artery disease] risk factor status, to have a medical evaluation by a physician before embarking on a program of moderate (i.e., exercise intensity 40 to 60 percent VO2max) exercise training,” according to the ACSM Guidelines for Exercise Testing and Prescription.3 In this case study, the 50-year-old firefighter`s corresponding heart rates for a 40 to 60 percent VO2max are listed in the box above.
For this subject, a submaximal test that produces a heart rate of 134 or less is safe to perform based on ACSM guidelines. Firefighters considered high risk could wear a heart rate monitor to ensure that the heart rate limit is not exceeded.
CASE STUDY CONCLUSION
The results presented in the box on page 54 support the conclusion that varying paces can be performed with good results. The first trial at 30 percent of VO2max, a “walk to the mailbox pace,” is too slow to be effective. The second trial, though an improvement, is still 3 ml below the most accurate score. The third trial, at 40 percent, appears to represent the minimum level for a good estimation. For this individual, therefore, efforts ranging from 40 to 80 percent represent acceptable intensity levels that will produce good results. Trial 5 produced the same score as the maximal effort in Trial 6 at a lower intensity, without undue stress or muscular discomfort for the subject, supporting the theory that a maximal effort is not essential. The last trial (6) was the subject`s maximal effort representing 80 percent VO2max and approximately 90 percent maximum predicted heart rate, the upper limit recommended by the ACSM. Based on the ACSM guideline, this subject could be safely evaluated without prior medical clearance and with reasonable accuracy (within 1 ml of his max effort) in the 40 to 60 percent range.
TEST ADVANTAGES
Having used this test for eight years, I have had the opportunity to assess the advantages and limitations of this method. I conclude that the advantages far outweigh the few negatives found and that few field tests can compete with the Rockport Walking Test. Some of the advantages include the following:
Ease of administration. The test requires minimal equipment, a stop watch, and access to a measured track. A large number of people can be tested at the same time, expediting the test process and minimizing “out-of-service” time. The test can also be performed on a treadmill if desired.
The test was validated using a broad age range (30 to 69) of men and women who were heterogeneous in VO2max. This enables generalization to a broad population, including firefighters, which cannot be done with many tests.
The correlation of the walk test to the max V02 test is quite high, r = 0.88 (excellent) with a standard error of estimate (SEE = .4.98) and cross-validation reporting r = 0.92. Most tests do not conduct cross-validation or provide a measure of the SEE that describes the accuracy of prediction.
The test does not require a maximal effort, as demonstrated in the case study, with accurate assessments reported with intensity efforts from 40 to 80 percent of max VO2. Variations in walk time are accompanied by adjustments in heart rate that preserve the accuracy of the VO2max estimate when entered into the formula.
Unlike running tests where pacing significantly affects the outcome, walking is fairly easy to pace. The lap time splits (case study) varied from three to nine seconds, indicating that pace is easy to maintain even for the inexperienced. The even pace was also reflected in the lap-time splits for heart rate, which ranged from two to eight bpm. Unlike running tests, the time factor alone does not determine the VO2 score. This eliminates the “competitive” environment, since the results are completely individual and unrelated to coworker efforts. For this reason, the fastest time in a group does not necessarily result in the highest score, removing the need to compete.
Walking is virtually injury free with the landing force of foot plant about one to one and one-half one`s body weight, compared with running forces of three to four times the body weight. This is particularly important for firefighters who weigh 180 pounds or more.
Since the test can be performed at varying paces and intensities with good results, it is a safe and effective alternative for overweight or high-risk individuals. The results of the test can then be used to prescribe walking programs, which is an excellent mode of training for such individuals. Using this test helps promote walking activities both on and off the job. Both “fun” walks and competitive walking events are popular community activities a firefighter can pursue off-duty with the added benefit of involving the whole family.
Firefighters can “self-test” themselves periodically, providing an accurate estimate of their aerobic condition, thereby allowing an individual to adjust his exercise routine to maintain the desirable level of conditioning.
The training concept of “specificity” also applies to test protocols, which means the test should be specific to the training mode. A runner, for example, is best evaluated with a run test and a cyclist with a cycle ergometer test. Since all modes of training cannot be accommodated logistically with an exercise-specific test, the walk test is the best alternative for an accurate assessment. Everyone is familiar with walking.
TEST LIMITATIONS
The limitations I found are as follows:
Faster paces require the development of a technique.
The anterior tibialis (shin) muscle becomes irritated in fast walking.
Lack of participant cooperation is a problem.
Since an accurate assessment can be achieved at a comfortable pace, the first two problems are easily rectified. The anterior tibialis is typically a weak muscle, and fast walking will help strengthen it. Once strengthened, the problem will disappear. Improvement in walking technique is unnecessary for test purposes but would prove useful if you desire to become involved in competitive race walking or exercise at higher intensities. The third problem is present with all types of tests. To minimize adverse responses, I suggest emphasizing the purpose of the test–which is to get an accurate score–and explaining the types of behavior that can interfere with this goal.
RECOMMENDATIONS
In conducting the test, the administrator should emphasize the objective: to determine an accurate estimation of aerobic capacity. This requires an honest effort. An even pace should be maintained for all four laps. Participants should be instructed to perform “as fast as possible,” since a pace less than maximal effort may be too slow for an accurate score, as was reported with Group B. If a lower intensity is desired for specific high-risk members, a heart rate monitor should be worn to maintain the desired heart rates.
The competitive aspect should be discouraged because it often produces poor results. Individuals attempting to race each other will almost always lead to uneven laps and an inaccurate estimation, thereby removing the benefit of the assessment. Others may “play” with the formula by walking fast for three laps and then slowing down toward the end to lower their heart rate and hopefully receive a better score (the formula adjusts). The goal is an accurate score! Emphasize this, since the test is designed for the benefit of the end-users by providing valuable information on their health status.
* * *
The results of the firefighter study support the use of the one-mile walk test for the assessment of aerobic capacity in firefighters. The coefficient of correlation r =.88 is consistent with the results of the original study, supporting the proposition that the one-mile walk test is one of the most accurate, if not the most accurate, submaximal field tests available today. The case study demonstrates the accuracy of the test within a range of intensities (40 to 60 percent VO2max), which provides a safe and accurate alternative for sedentary and older firefighters. The walk test is an excellent field test option for firefighters and is highly recommended for inclusion in the department`s fitness test battery. n
Endnotes
1. Kline, G. M., J. P. Porcari, et al., “Estimation of VO2max from a one-mile track walk, gender, age, and body weight,” Medicine and Science in Sports and Exercise, 1987, 19; 253-259.
2. “The Rockport Guide to Fitness Walking” is available through the Rockport Walking Institute, P.O. Box 480, Marlboro, Massachusetts 01752.
3. The ACSM Guidelines for Exercise Testing and Prescription, 4th ed. (Philadelphia: Lea & Feibiger, 1991).
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JOHN LECUYER is a 19-year veteran of the Aurora (CO) Fire Department and currently serves as the health and safety officer. He has degrees in several fields, including a master?s in kinesiology. He is a member of the NFPA 1500 Occupational Safety and Health Committee.
