ABSTRACT
Physical therapists frequently interact with patients, including children and older adults, who are deconditioned due to decreased physical activity associated with sedentary lifestyle, injury, disease, or disability. Objective quantification of aerobic capacity provides a baseline of patient performance, informs the evaluation and intervention process, and establishes the efficacy of interventions. The purpose of this article is to review field tests of aerobic capacity, including walk tests, step tests, and shuttle tests, for use in the pediatric and geriatric populations. Aerobic capacity of healthy children can be evaluated using walk tests, shuttle run tests, and step tests. To determine aerobic capacity in children with cystic fibrosis or who are severely ill, time-based walk tests, step tests, and shuttle walk tests are appropriate. Field tests of aerobic capacity for healthy older adults include walk tests, step tests, and shuttle walk tests, whereas for older adults with cardiorespiratory, neurologic, or orthopedic impairments time-based walk tests and shuttle walk tests are used. Field tests are safe, easily administered, and require little equipment. Using standardized administration, these field tests provide valid and reliable estimates of aerobic capacity for pediatric and geriatric patients that can be used to inform exercise prescription and quantify the efficacy of therapeutic interventions.
INTRODUCTION
Many of the patients that physical therapists interact with are deconditioned due to decreased physical activity associated with injury, disease, or disability.1,2 Increasingly, however, low activity levels are becoming the norm even within the 'healthy' population. Decline in physical activity has been observed in every segment of the population, including pediatric and geriatric populations. A recent study of healthy children ages 4 to 1 8 years found that 60% to 80% had fitness levels below the 25th percentile.3 Similarly, more than 50% of persons 65 years and older are reported to have a sedentary lifestyle.4
The importance of physical activity in maintaining and improving cardiopulmonary fitness and reducing the risk of type II diabetes mellitus and cardiac events, such as myocardial infarction, stroke, and sudden death, can not be overstated. Indeed, recent studies have demonstrated that individuals with average cardiopulmonary fitness have 50% reduced incidence of mortality and morbidity from cardiac events as compared to those with low fitness levels.1 As health care professionals with education and experience in the evaluation of a patient's functional capacity, physical therapists are ideally situated to identify individuals with low cardiorespiratory fitness and provide positive management interventions.
To optimize a patient's functional recovery and prevent the sequelae of low cardiorespiratory fitness, objective quantification of aerobic capacity is essential. Field tests of aerobic capacity provide baseline information that permits the identification of improvements in cardiorespiratory fitness resulting from therapeutic interventions. Determination of aerobic capacity is ideally performed in an exercise testing laboratory utilizing specialized equipment and maximal exercise protocols on either a treadmill or a cycle ergometer to measure maximal oxygen consumption (VO^sub 2^max), the 'gold standard' measurement of cardiorespiratory fitness. However, the availability of these specialized testing environments is often limited to specific patient populations, such as individuals with cardiac disease or athletes. Additionally, many deconditioned patients may not tolerate the metabolic demands of maximal exercise testing. Alternatively, cardiorespiratory fitness determined by submaximal testing using either treadmill or cycle ergometer protocols has been found to be highly correlated with measurements obtained using maximal protocols. Thus, reliable and valid submaximal treadmill and cycle testing protocols have been developed and used in numerous clinical settings and with various patient populations.5 Unfortunately, many physical therapists do not have access to treadmills or cycles in their clinical settings.
In this regard, exercise tests requiring minimal equipment are available for the determination of cardiopulmonary fitness. These field tests provide reliable and valid correlates of aerobic capacity and thus provide a standardized measurement that can be used in most clinical settings with many patient populations.6,7 Utilization of standardized measurements of aerobic capacity allow for appropriate exercise prescription and provide an objective measure of the efficacy of a physical therapists' intervention. The purpose of this article is to review field tests for the determination of aerobic capacity with the goal of providing physical therapists with easily implemented measurement tools with which to quantify the aerobic capacity of pediatric and geriatric patients. The field tests of aerobic capacity reviewed in this article include walk tests, step tests, and shuttle tests.
WALK TESTS
Introduction
Walk tests are simple, inexpensive, safe, and reliable tests for the measurement of functional exercise capacity and the monitoring of treatment effectiveness. Most commonly used walk tests are the time-based walk tests that measure the distance covered in the specific time period. These include the 12-min walk test (12MWT),8 6-min walk test (6MWT),8-10 and the 2-min walk test (2MWT).8 Alternatively, distance-based walk tests, such as the 400-m walk test,11,12 and the 1-mile walk test,13 measure the time taken to complete the specified distance.
The advantages of walk tests include the ease of administration, minimal equipment requirements, and a high degree of validity and reliability. Patients from 5 years14 and older10 are able to perform the 6MWT. These tests employ a functional activity that patients are familiar with. Patients who use assistive devices are also able to perform these tests. Corridor walking is generally more acceptable to older participants than is treadmill walking15 as they may experience physical difficulty and anxiety when walking on a treadmill.11,15,16 This can result in an underestimation of functional capacity as compared to walking in a hall or corridor.17
Standardization of the testing procedure is essential for obtaining accurate results.9 The use of standardized instructions is recommended as verbal encouragement has been shown to influence the results of the 6MWT.18 A practice may be considered, but is not thought to be essential as the resulting increase in walk distance ranges from 0% to 1 7%.9 If a practice test is performed, it is recommended to wait one hour prior to performing another test.9 Disadvantages of the time-based walk tests include the reliance on patient motivation to achieve a valid test.19 The 400-m walk test is thought to be intrinsically more motivating owing to the patient focusing on finishing the distance and not walking for a set time.11 Indeed, comparison of the 6MWT with the 400-m walk test demonstrated that individuals aged 70 to 79 years achieved a 20% greater walking speed (m/sec) during the 400-m walk test than with the 6MWT.11
The 6MWT is the most commonly used of the walk tests. Following the introduction of the 12MWT,8 the test was subsequently shortened to 6 minutes without a loss of validity or reliability.8 The 6MWT has been used with many patient populations, including pediatric20-22 and geriatric patients,10,15,23-27 and has been the subject of several recent reviews.7,9,28 Recently, the 2MWT has been gaining popularity for use with patients who are unable to sustain exercise for 6 minutes. The 2MWT has been used in severely ill children,14 the frail elderly,26 and individuals with respiratory symptoms,8,29 cardiac surgery,30 neurological disorders,31 and lower limb amputation.32 With respect to the distance-based walk tests, the 400-m walk test appears to obtain superior performance in older individuals as compared with the 2MWT and the 6MWT11,12 and is able to discriminate walking ability and fitness.11 The 1 mile walk test is not used very often in the pediatric or geriatric populations because many of these patients are unable to walk 1 mile.
Administration
Time-based tests (12MWT, 6MWT, 2MWT)
Distance is the primary outcome measure obtained with these tests. Using standardized instructions,8,9 the patient is instructed to walk as far as possible in the specified time. The patient is permitted to slow down, stop, and rest as necessary. The American Thoracic Society (ATS) recommends an indoor course of 30 m with marks every 3 meters, but corridors of longer and shorter distances and the use of indoor tracks have been cited in the literature.9,27
Distance-based tests (400-m walk, 1-mile walk)
Time is the primary outcome measure obtained with these tests. These tests use standardized instructions11-13 to direct the patient in performing the required distance as quickly as possible at a pace that they can maintain. The course for the 400-m walk test is 20 m (with marks every meter) and the patient performs a 2-min 'warm up walk,' by walking at a pace that they can maintain for the 2 minutes. After a 60-second rest period, the patient begins the 400-m walk test by performing 10 laps of the course.
Determination of Aerobic Capacity (VO^sub 2^)
The energy expenditure during the walk test can be determined from the walking speed that is calculated from the distance walked during the specified time period. Since the patients are instructed to perform a maximal effort during the test, the energy expenditure correlates well with measures of maximal aerobic capacity measured on the cycle or treadmill.23,29 The walking speed obtained from any of the walk tests (both time-based and distance-based) is used to calculate aerobic capacity as shown in Table 1.
Normative Values
There are several published reports of normative values for distance walked for the 6MWT for community dwelling elderly individuals and those residing in retirement homes (Table 2).
STEP TESTS
Introduction
Step test are field tests of aerobic capacity that require the participant to step up and down from a platform. Aerobic capacity determined by step tests has been shown to correlate well with aerobic capacity determined by treadmill33-35 and cycle ergometer exercise36-37 protocols. Step tests use the post-exertional heart rate response to predict oxygen consumption. Step tests are submaximal tests, though they often impose higher metabolic costs than self-paced walk tests and thus result in higher heart rates.38 Step tests can be single-stage or multistage; externally paced or self paced; have continuous or discontinuous work loads; and have predetermined, arbitrary end points. Externally paced step tests require the participant to maintain a set stepping rate for a specified time period and thus this test is relatively free of the variability associated with patient motivation as occurs in a self-paced step test or walk test such as the 6MWT.39 Other advantages of the step test include safe, simple, quick administration and portability.
The Harvard Step Test40 was one of the earliest reported step tests. This maximal effort test used a single stage work level that required participants to step up and down a 20-inch bench at a rate of 30 steps per minute for 5 minutes. The recovery heart rate was used to determine aerobic capacity.40 Due to the high exertion level and the demands on the leg muscles resulting from the high step height, the Harvard Step Test has subsequently been modified. Currently employed externally paced step tests use step heights between 6 and 20 inches, stepping rates between 18 and 36 steps per minute, and time periods between 2 and 6 minutes.34,37,39,41 These tests have been validated in healthy individuals between 7 and 18 years36,42 and over the age of 65 years38,43 as well as in children with cystic fibrosis39,41,44 or who are blind36 and older adults with chronic obstructive pulmonary disease.45
Studies have examined the relevance of step height in the accurate prediction of oxygen consumption.35,46 The findings demonstrated that varying the step height to accommodate the individual's stature may35,47 or may not46 result in more accurate prediction of aerobic capacity. To account for this inconsistency, predictive equations often incorporate step height into the calculations.48
In healthy children ages 7 to 17 years, predicted VO^sub 2^max using the Canadian Step Test49 and the Canadian Home Fitness Test50 has been shown to have good correlation with VO^sub 2^max as determined by treadmill testing.36,51 More recently, a 3 minute single stage externally paced step test was developed to assess aerobic capacity in children with cystic fibrosis.41 In one study of children with cystic fibrosis (age 7-18 years; FEV^sub 1^ = 17-67% predicted), this 3 minute step test produced a greater rise in HR and a greater fall in SaO^sub 2^ than the 6MWT, especially in children with more severe lung disease.39 Therefore, the step test was suggested to be rigorous enough to be a valuable assessment tool when assessing a child's suitability for lung transplantation.39
For adults older than 65 years, the single stage43,45 and multistage50,52 step tests have been shown to be valid. Recently, a self-paced step test for individuals over 65 years was introduced and was found to be highly correlated with aerobic capacity measured on a treadmill.38 This test was able to identify individuals of differing functional capacities and was found to be sensitive to the changes in fitness levels.
Administration
Single stage externally paced step tests
The most commonly used step test for children and older adults is a single stage externally paced step test using a 3-minute time period, cadence of 26 steps/min (adults) or 22 steps/min (children), and a step height that is appropriate for the individual's stature. The equipment required for the step test includes a step and a timer. Participants step up and down a single step such that the feet both go up and then both return to the initial level (ie,"up-up-down-down"). The stepping rate is indicated by a metronome set at 4 times the cadence so that each foot movement is associated with a sound. The stepping procedure is demonstrated to the patient prior to the test so that they understand the stepping sequence. Standardized encouragement may be given.44 The test is completed when the patient chooses to stop, the SaO^sub 2^ drops below accepted standardized levels, or the 3-minute stepping period is completed. The HR is measured for 15 seconds within 5 seconds of the completion of the test.42
Single stage self paced step test
This relatively new step test consists of stepping up and down 2 small steps [each 20 cm (8 inches) in height)] 20 times at a self selected pace.38 The step pattern is up-up-up-down-down-down using alternate legs. The arms are freely hanging at the patient's side and no railings are used. The test begins with a familiarization period in which the participant steps up and down the steps 10 times at a 'slow' pace to ensure that they are able to perform the stepping rhythm. Following a rest period of 5 minutes or until the HR has returned to within 5 beats per minute of the resting rate, the participants perform 20 step cycles at a 'normal' pace. Immediately following the 20th cycle, the time (in seconds) to complete 20 step cycles and HR (counted for 15 seconds) are determined.
Normative Values
Single stage externally paced step tests
Due to the nature of this test being a predictor of maximal aerobic capacity, there are no normative values beyond those for VO^sub 2^ for the specific age group or patient population.
Single stage self paced step test
In a recent study of 108 females and 92 males ≥ 65 years (average 72 �4 years),38 time to complete 20 step cycles at a 'normal' speed was 122 � 4 sec for females and 126 � 4 sec for males.
SHUTTLE TESTS
Introduction
The Shuttle Walk Test (SWT) is a standardized, incremental walking test that measures functional capacity by exercising an individual to a symptom limited maximal performance.53-55 The SWT was originally developed by Singh and colleagues53 and was based on the 20-m Shuttle Run Test.56 These incremental exercise tests require patients to walk (10-m test) or run (20-m test) at increasing speeds back and forth a 10-m or 20-m course. The speed of walking is increased every minute and is controlled by audio signals played from a tape.53-55 The external pacing of this test overcomes the motivation limitations that have made other self-paced step tests and walking tests, including time-based tests such as the 2-, 6-, and 12-minute walk tests,8 less attractive as objective measures of functional capacity.53,54,56
The SWT was designed to assess functional capacity in patients with chronic obstructive pulmonary disease (COPD)" and has been validated in the elderly (≥ 70 years)55 and in older patient populations with cardiac pacemakers,57 heart failure,58-61 patients awaiting heart transplant,62 idiopathic pulmonary fibrosis,63 and younger adult populations with cystic fibrosis.64 (See Cardiopulm Phys Ther J. 2005;16(2):21-23). The SWT has also been used to evaluate children under the age of 7 years.65,66 The Shuttle Run Test has been validated for healthy children66-70 and children with cystic fibrosis65 and asthma.71
Administration
Standardized instructions" for the test are provided on an audiocassette tape (available from the developers at sally.singh@glenfield-tr.trent.nhs.uk). The test uses a quiet corridor or treatment area at least 12 meters (10-m test) or 22 meters (20-m test) in length. Patients are required to walk (10-m test) or run (20-m test) back and forth, turning around 2 cones that are placed 9 meters (10-m test) or 19 meters (20-m test) apart, providing a shuttle distance of 10 or 20 meters, respectively, while keeping pace with a prerecorded auditory signal.
The patients aim to set a pace to complete a shuttle as each bleep sounds. Every subsequent minute, the audio signal sounds at increasingly shorter intervals. Each shuttle is indicated by a single bleep on the tape, whereas speed increases every minute are indicated by a triple bleep. The velocity of the 10-m shuttle test is set at 0.5 m/s for the first level and increases by 0.17 m/s every level thereafter. The 20-m shuttle test begins with a velocity of 4 km/hr at level 1 and increases by 0.5 km/hr every subsequent level. There are 12 levels with each level requiring the patient to perform successively more walks (shuttles) within the 10-m or 20-m course.
Distance walked in the SWT is recorded in meters (calculated as the number of shuttles x 10 m/shuttle). No encouragement may be provided to the patient. The test is terminated when the participant chooses to stop or when on 2 consecutive paced signals the patient is more than 1 m away from the closest marker.53 The SWT and Shuttle Run Test can be carried out in any clinical setting without the need for special facilities and can be completed in 15 minutes.
SUMMARY
Physical therapists are encountering more patients who are deconditioned due to the increased prevalence of a sedentary lifestyle. The associated decrease in aerobic capacity is occurring across the lifespan, including the pediatric population. Physical therapists are uniquely suited to identify deconditioning and to prescribe interventions to promote the attainment of increased fitness and health. Field tests of aerobic capacity, including walk tests, step tests, and shuttle tests, provide the physical therapist with valid, reliable outcome measures to quantify the aerobic capacity of their patients in most environments. These tests are safe, require little equipment, and employ functional activities. Aerobic capacity of healthy children can be evaluated using walk tests, shuttle run tests, and step tests. To determine aerobic capacity in children with cystic fibrosis or who are severely ill, time-based walk tests, step tests, and shuttle walk tests are appropriate. Field tests of aerobic capacity for healthy older adults include walk tests, step tests, and shuttle walk tests, whereas for older adults with cardiorespiratory, neurologic, or orthopedic impairments time-based walk tests and shuttle walk tests are used. Using standardized administration, these field tests provide valid and reliable estimates of aerobic capacity for pediatric and geriatric patients that can be used to inform exercise prescription and quantify the efficacy of therapeutic interventions.
ACKNOWLEDGEMENTS
PJO is supported by grants from the American Lung Association and the Interdisciplinary Research and Creative Activities Fund at the University at Buffalo.
[Reference]
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[Author Affiliation]
Patricia J. Ohtake, PT, PhD
Associate Professor, Program in Physical Therapy, Department of Rehabilitation Science, University at Buffalo, Buffalo, NY
[Author Affiliation]
Address correspondence to: Patricia J Ohtake, PT, PhD, Department of Rehabilitation Science, 515 Kimball Tower, University at Buffalo, Buffalo, NY 14214 Ph: 716-829-3141 ext 142, FAX: 716-829-3217 (ohtake@buffalo.edu).
