The incremental shuttle walk test (ISWT) is a field-based assessment of cardiorespiratory fitness and physical function (1–4).
PURPOSE OF THE ASSESSMENT
The ISWT was originally designed to determine cardiorespiratory fitness and functional capacity and to predict mortality and morbidity in specific populations with chronic medical conditions (1,3–16) and more recently in apparently healthy, relatively inactive populations (17–22). It is a safe, fairly simple test to learn and administer and should be considered a viable alternative to treadmill or bicycle ergometer testing for apparently healthy, nonathletic clients.
The ISWT, originally designed by Singh et al. (1) for persons with chronic obstructive pulmonary disease (COPD), is a performance-based assessment of exercise and functional capacity that measures walking distance in meters (1,4). It is a relatively brief and easy test to perform. The ISWT simulates a maximal cardiopulmonary test in a field setting and requires minimal equipment (2,3,22,23). Performance (distance walked and therefore the maximal walking velocity) on the ISWT correlates strongly with direct measures of peak oxygen consumption (V̇O2peak) during treadmill and bicycle cardiopulmonary exercise testing (CEPT/CPXT), allowing the prediction of peak oxygen consumption (V̇O2) (1,2,4,6). Longer walking distances signify better performance (1,4). The ISWT has been validated for people being assessed for heart transplant (24), congestive heart failure (25), and intermittent claudication (leg cramping) from peripheral vascular disease (26) and for elderly people with and without airflow limitations (27). Results from the ISWT can direct exercise/rehabilitation program development and assess progress and efficacy (1,3,4,23). The ISWT can be used to determine functional walking capacity in people with stroke who require no additional assistance (especially in people with gait speeds of ≥0.8 m/second) (7). Although the 6-minute walk test is the clinical outcome measure of choice for endurance in people with COPD, the ISWT has been shown to be more accurate for assessing maximal exercise capacity and ventilatory (breathing) impairments (5). Woolf-May et al. (28) found that the approximate oxygen cost in metabolic equivalents (METs) for walking on flat or level ground correlated with those attained during the ISWT in apparently healthy, asymptomatic elderly men but was underestimated in age-matched males participating in phase IV cardiac rehabilitation after sustaining a myocardial infarction. They concluded that the ISWT is a valid field test for determining functional capacity in symptomatic individuals but stated that caution should be used when attempting to quantify MET levels from the walking speeds achieved during the ISWT in this population (28). The 6-minute walk test is a self-paced assessment, whereas the ISWT is externally paced (4,5,12). More recently, Probst et al. (29) and Jurgensen et al. (11) established reference equations for predicting reference values (how far a population should be able to walk) in the ISWT in healthy subjects 18 to 83 years old and in older adults ≥40 years old, respectively. Dourado et al. (17) determined that the ISWT is a valid instrument for assessing physical fitness in healthy adults ≥40 years of age and, thus, for designing individualized walking programs in that population. Both investigations were conducted in Brazil. Additionally, Agarwal et al. (18) and Itaki et al. (19) developed reference standards and prediction equations for the number of meters subjects should be able to walk during the ISWT in healthy Indian and Japanese adults. More recently, the ISWT has been shown to be a maximal test showing similar results with a maximal CEPT/CPXT in young healthy sedentary adolescent boys, healthy sedentary young and middle-aged men, and young healthy women. Validated prediction equations for assessing peak oxygen consumption (V̇O2peak) have been developed for each of these populations (20–22) (Figure 1).
Equipment necessary for administering the ISWT includes the following: a well-lit, level, nonslip walking surface (at least 15 m in length); a measuring wheel or metal measuring tape; two marking cones; bright colored masking/duct tape; and a sound system and recording of the beeps for each of the 12 test levels. A complete testing kit including an audio CD and test norms and instructions can be purchased from Prof. Sally Singh, Department of Respiratory Medicine, Glenfield Hospital NHS Trust, Groby Road, Leicester LE3 9QP, UK, or visit: http://www.leicestershospitals.nhs.uk/aboutus/departments-services/pulmonary-rehabilitation/for-health-professionals/incremental-shuttle-walk/ for further information on how to access.
The ISWT is a simple, multilevel, externally paced test requiring clients to walk progressively faster each minute. Although each of the 12 levels lasts 1 minute, the required number of 10-m trips (shuttles) between two opposite cones, the walking speed, and the corresponding oxygen cost increase incrementally. The point when clients fail to keep up with the beeps represents their maximal walking velocity and theoretically their peak oxygen consumption (V̇O2peak) (2,6).
It is important that clients understand all of the test directions and procedures before they start. To enhance safety, the examiner should provide a clear but brief explanation and then demonstrate one stage of the ISWT with the sound recording of the beeps audible (23,30). It is prudent for the examiner to ask the client to explain in their own words the directions they just received and to ask them if they have any questions. The client should perform at least one level of the ISWT as a practice trial to get used to walking with the audio beeps and have at least 3 minutes of recovery time before actual testing. Clients demonstrating difficulty, discomfort, or signs of unsteadiness during the practice trial should not perform the ISWT and should consult their health care provider (HCP) before being tested or initiating an exercise training program. Because of clients’ near or maximal level of exertion and effort during this test, examiners should follow the American College of Sports Medicine’s preactivity screening guidelines before administering this test (31). Clients with known cardiovascular, metabolic, or renal diseases and/or with symptoms suggestive of them should receive medical clearance before being tested (31). Clients should be free of musculoskeletal injuries, which would make performing this test uncomfortable and/or unsafe. The ISWT should not be performed by clients who have demonstrated unsteadiness when standing, difficulty getting up from a chair, difficulty following simple directions, impulsiveness, or confusion. Pre- and posttest measures of heart rate, blood pressure, and oxygen saturation should be assessed on all clients. The test should be administered on a well-lit slip-resistant surface that is free of glare and provides an extra safety zone of approximately 2 m to 3 m behind each cone so clients can turn and change directions safely. Figure 2 depicts the ISWT walking course. Spotting is not typically provided during this test, but a health and fitness professional or clinical exercise physiologist may walk behind and outside the client’s visual feed as long as they do not impair their walking progress or influence their pace. Table 1 shows contraindications to performing the ISWT.
TABLE 1 -
Contraindications to the ISWT
|Incremental Shuttle Walk Testing should not be administered if an older adult (>65 years) exhibits one or more of the following:
|1. Physician clearance found necessary or positive findings determined in the prescreening
|2. Presence of any absolute or relative contraindication associated with cardiovascular disease
|3. Signs or symptoms of cardiovascular, metabolic, or renal disease exhibited before test
|4. Presence of musculoskeletal or neurologic conditions that can impair static and/or dynamic balance; signs of confusion, dementia
|5. The client cannot ambulate free of assistive devices (i.e., walker, cane, etc.)
|6. Inflammation of joints and/or joint pain associated with orthopedic conditions/injury; limping
|7. Presence of cognitive deficit (determined but not limited to a Mini-Mental State Exam score <17); signs of confusion, dementia
|8. Testing environment poses safety hazard (slippery conditions, poorly lit area)
|9. The client requests to not perform or to stop the assessment.
The test is comprised of 12 levels or stages. Each stage lasts 1 minute (60 seconds). Participants are required to complete progressively more “shuttles” (one-way trips) between the two cones during each successive level/stage. The shuttle distance from the back of one cone to the back of the other cone is 10 m. A horizontal tapeline should be placed on the floor exactly 0.5 m in front of each cone. This serves as a “warning zone.” Each stage begins after the sound of three successive beeps (“Beep, Beep, Beep”), and clients should begin walking promptly at a brisk pace after the third beep. Clients must walk to and be behind the opposite cone before the sound of one single beep. They should wait behind the cone until they hear the beep if they arrive early. It is this time between single beeps which gets progressively shorter during each level or stage that makes the test progressively more difficult (23,30). Clients are more likely to arrive early to each cone during the first few levels or stages and then find it exceedingly more challenging to arrive behind the cones on time in later stages as they approach their maximal walking velocity. Clients should always be behind the opposite cone before the sound of a single beep and always begin walking briskly toward the opposite cone as soon as they hear a single beep. Therefore, you should instruct the client in the following manner, “You should strive to always arrive behind a cone before each single beep and start walking to the opposite cone on each single beep.” Clients are given a one-time warning to speed up and to keep up with the beeps if they are no more than 0.5 m away from the cone or inside the “warning zone” created by the tapeline. The test is terminated when clients are either more than 0.5 m away from the opposite cone on a single beep, demonstrate excessive fatigue, have other signs or symptoms of exercise intolerance, or say that they want to stop. The ISWT begins at a walking velocity of 0.5 m/second and increases by 0.17 m/second each stage. Three shuttles must be completed in 1 minute during stage one and are separated by three single beats occurring every 20 seconds. Eight shuttles must be completed in 1 minute during stage six and are separated by eight single beeps occurring every 7.5 seconds. Fourteen shuttles must be completed in 1 minute during the 12th and final stage and are separated by 14 beeps occurring every 4.29 seconds.
The point when a client fails to keep up with the beeps represents their maximal walking velocity and theoretically their peak oxygen consumption (V̇O2peak) (2,6). Typically, the ISWT is performed twice. According to Probst et al. (29), approximately two-thirds of subjects perform better on the second test trial than the first, and the distance between two trials can vary between 20 m and 40 m. The greatest distance of the two trials should be counted as the maximal walking distance. Table 2 depicts the measurable variables during each level/stage of the ISWT (walking velocities, number of shuttles, distance walked, time to complete each shuttle, and approximate oxygen cost in METs).
TABLE 2 -
The Measurable Variables during Each Level/Stage of the ISWT
||Time between Each Single Beep during Each Stage
||Number of Shuttles
|Level Stage (Levels Begin with 3 Consecutive Beeps)
||Time/Shuttle between Single Beeps (seconds)
, volume of oxygen consumed (1,28
It is important at the end of the ISWT that the examiner asks each client to explain in their own words what stopped them from either continuing or keeping up with the audio beeps. Their responses should be recorded and along with their results, compared later during serial retesting. A general, 5- to 10- minute warm-up before testing is prudent. Please refer to digital video content file 1 for a description of how to orient a patient or client before administering the ISWT (Supplemental Digital Content 1, https://links.lww.com/FIT/A176). Please refer to digital video content file 2 for a demonstration of proper administration and execution of the ISWT (Supplementary Digital Content 2, https://links.lww.com/FIT/A177).
A detailed discussion of signs of movement dysfunctions during ambulation tasks is beyond the scope of this article. However, exercise professionals should recognize general signs like limping; shuffling; visual or verbal manifestation of pain and discomfort in the spine, joints, or extremities; and excessive shortness of breath and exhaustion warranting immediate test termination and communication with a physician or other qualified HCP. Table 3 describes some observable signs of potential movement dysfunctions, which can jeopardize client safety during the ISWT and subsequent exercise sessions.
TABLE 3 -
Observable Signs of Potential Movement Dysfunctions Warranting Consultation with a Health Care Provider
||Forward flexion of the spine
||Postural imbalance, weak paraspinals, tight hip flexors, osteoporosis, low back pain and potential balance decrements, and elevated fall risk; new or worsening pain warrants test termination and communication with an HCP
||Limited hip flexion of the swing leg to clear the foot from the ground
||Weak hip flexors and core muscular; if this is a new occurrence, communication with an HCP is warranted before testing
||Difficulty or inability to extend knee/hip of the stance leg and support the body during swing of the contralateral leg/foot
||Weak hip and knee extensors on stance leg may increase fall risk; if this is a new occurrence, communication with an HCP is warranted
||Inability to dorsiflex the ankle to clear the toes from the ground or presence of foot drop on the swing leg
||May indicate anterior compartment muscle weakness of lower leg and neurologic involvement from spine/hip or lower leg; may increase fall risk; if this is a new occurrence, communication with an HCP is warranted before testing
||Extra wide base of support, slow movement, hesitation, and/or freezing especially around cones
||May indicate cerebellar dysfunction, vestibular dysfunction, visual impairment, Parkinsonism, motor programming, and planning deficits, or other conditions; may place clients at an elevated fall risk; warrants communication with HCP before testing
||Decreased stance time on one limb or limping
||Potential pain and subsequent antalgia; this warrants immediate test termination and communication with an HCP
Swing leg, leg transitioning (open-chain) advancing forward; stance leg, leg that is fixed (closed-chain) on the ground.
Table 4 provides prediction equations of V̇O2peak from performance in the ISWT in select populations (20–22).
TABLE 4 -
Prediction Equations of V̇O2peak
from Performance in the ISWT in Select Populations
|Lima equation in healthy women
V̇O2peak (predicted) = 19.793 + (0.02 × distance walked) – (0.236 × age). There was no statistically significant difference between the V̇O2peak measured directly and the predicted.
|Neves equation in sedentary healthy middle-aged and elderly males
V̇O2peak (predicted) = 37.44 – (1.081 × BMI) + (10.151 × gait speed)
*Gait speed refers to the maximal speed attained in meters/second during the final level/stage performed during the ISWT.
|Gomes equation in healthy sedentary adolescent boys
V̇O2peak (predicted) = 20.94 + (0.02 × distance walked)
**Distance walked refers to the total accumulated distance at the end of the ISWT.
MINIMAL CLINICALLY IMPORTANT DIFFERENCE
Many valid performance and function tests have a reported minimal clinically important difference (MCID). The MCID is the smallest change in an exercise or rehabilitation program outcome that an individual client or patient would identify as important and which would indicate a change in the client’s or patient’s management. The MCID is helpful when designing exercise and rehabilitation program goals and measuring program outcomes. In some cases, MCIDs for a test or assessment differ for specific populations (cardiovascular disease, congestive heart failure, elderly, stroke, COPD, apparently healthy sedentary adults, etc.) Therefore, it is important to refer to the appropriate MCID when administering the ISWT or other assessments within specific populations. Originally, Singh and associates (32) found that patients whose ISWT distances improved after pulmonary rehabilitation by 47.5 m and 78.7 m reported feeling “slightly better” or “better,” respectively, and they recommended that these distances be considered the MCID in this population. More recently, Evans and Singh (8) have recommended using between 35 m and 36.1 m as a minimal important difference in ISWT distance in patients after 7 weeks of pulmonary rehabilitation. Walsh et al. (33) have found 58 m to be the MCID in a small, young patient cohort with bronchiectasis, a chronic disorder causing permanent damage, widening, and thickening of bronchial tubes accompanied by frequent infections.
The ISWT is a safe, valid, reliable, and inexpensive field assessment of cardiorespiratory fitness and function. It can be adapted to meet the needs of apparently healthy elderly clients and frailer clients with a number of chronic medical conditions. It is easy to administer, and exercise professionals can use results to better develop individualized exercise programs and to monitor program results and effectiveness.
The authors thank Dr. Jonathon Mendola, P.T., CSCS, for all videography and photography.
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