Walking Speed: Reference Values and Correlates for Older Adults

Transcription

1 Walking Speed: Reference Values and Correlates for Older Adults Richard W. Bohannon, EdD, MS, BS' A. Williams Andrews, MS, BS Michael W. Thomas, BS he walking speed of older adults is important both because of its implications for community ambulation (23,29) and because of its relationship with consequential variables, such as discharge disposition (1 2), independent living (5), and fall history (19). This importance, combined with speed's objectivity and correlation with other measures of gait performance ( 14,18), justifies the use of speed as a descrip tor of gait among patients with orthe paedic disorders (3,20,27,31,34,38). The extent to which gait speed is reduced in orthopaedic patients can only be quantified, however, when reference values from apparently healthy individuals are available for comparison. Although numerous researchers have documented the gait speed of healthy subjects (Table 1) (2,6,7,11,13,17,22,24,30), the researchers' methods or their descrip tions of their methods limit the value of the speeds they report. In some studies, the measured subjects' characteristics and their intended speed (eg., in observational studies of pedestrians) are not known (1 l,30). Some research involves distances that are unspecified (21) or that surpass the capacity of many institutionalized patients (2). Much of the research employs laboratory equipment not available to most clinicians (1 7,22, 24). In studies where gait is described Speed is established as an important aspect of gait. This research was performed to establish reference values for comfortable and maximal gait speed and to describe the relationship of selected variables with speed. Apparently healthy men (N = 77) and women (N = 79), age years, participated. Their gait speeds were determined using a stopwatch. The static strength of five lower extremity muscle actions was measured with a hand-held dynamometer. As gait speed was found to correlate significantly with gender, separate reference values are presented for men and women. Muscle strength correlated more highly with maximal gait speed than with comfortable gait speed. Correlations of maximal speed with strength (except ankle dorsiflexion) were all significant at p <.001. Multiple regression analysis selected gender, body weight, and hip flexion strength as the best set of predictors of both speeds. The speed data presented here may be useful for patient comparisons. The correlations provide limited support for measuring and treating muscle strength deficits among the elderly with walking speed limitations. Key Words: gait, measurement, age ' Professor, School of Allied Health Professions, University of Connecticut, U- 101, Storrs, CT Senior Therapist, Department of Physical Therapy, University of North Carolina Hospitals, Chapel Hill, NC merely as timed, the specific method of timing is not clear (2,6,13). Clinicians seeking to make judgements about the normalcy of their patients' gait speeds would benefit from reference values obtained using methods which they too can employ. Researchers describing the gait speed of healthy individuals sometimes have examined the relationship of speed with assorted independent variables, including muscle strength (2,6,8,9,13, 16,17). Such examinations, however, have not typically included strength measurements from multiple muscle groups or addressed the relative importance of muscle strength as a determinant of gait speed. For the clinician interested in a patient's gait speed, a knowledge of factors associated with that speed are important. The purposes of this study of a p parently healthy 5@ to 74yearalds are: I) to present reference values for comfortable and maximal walking speeds obtained using a clinically applicable method and 2) to describe the relationship of the speeds, with a selection of subject characteristics and lower extremity muscle strength variables. METHOD This study was approved by the institutional review boards of the University of Connecticut, Storrs, CT, University of North Carolina at Chapel Hill, Chapel Hill, NC, and Hartford Hospital, Hartford, CT. The study was cross-sectional, including both descriptive and correlational components. Volume 24 Number 2 August 1W6 JOSPT

2 RESEARCH STUDY Gender Age Subjects Speed - ( ~m/se~) Reference (yean) (M X SD and male TABLE 1. Comfortable gait speed measurements reported in seven studies of healthy adult subjects. Subjects A convenience sample of 156 subjects participated following the provision of written informed consent. The subjects consisted of 77 men and 79 women, age years. All were able to walk at least 30 m and were without known neurologic, orthopaedic, or cardiopulmonary problems that would compromise their performance or well-being. Table 2 summarizes the subjects' characteristics by gender. Instrumentation Gait speed was calculated from measures of walking time obtained with a digital stopwatch. The watch measures time to the nearest.ol second. Lower extremity muscle strength was measured with a Chatil- Ion CSD 400C hand-held dynamometer (John Chatillon and Sons, Inc., Greensboro, NC). The dynamometer, which measures force in pounds to the nearest.1 Ib (.44 N), has a ceiling of 115 Ibs ( N). The spe- cific dynamometers used in this study were calibrated before the start of the study and checked for accuracy midway through the study period. Moreover, the accuracy of the dynamometers was verified by the manufacturer at the completion of the study. Procedure Following the documentation of subject characteristics, comfortable and maximum walking speed were both measured twice while subjects walked over a 7.62-m (25 feet) expanse of smooth uncarpeted floor. Several meters were provided for acceleration and deceleration at each end of the test distance, which was marked by lines on the floor or adjacent wall. The stopwatch was started as subjects crossed the starting line and stopped when they passed the finish line. Speed was calculated by dividing the test distance by the time required to traverse it. During the comfortable walking speed trials, sub jects were instructed to walk at their normal comfortable speed. During the maximum speed trials, they were asked to walk as fast as they could safely without running. The method of measuring muscle strength with the hand-held dynamometer has been described extensively elsewhere (1). Briefly, five lower extremity muscle actions (hip flexion and abduction, knee flexion and extension, and ankle dorsiflexion) were measured twice on both the nondominant and dominant sides using isometric (make) tests. Dominance was determined by asking the subjects their preferred lower extremity for kicking a ball (4). Each action was measured by one of three experienced testers whose interrater reliability has been established (1). The limb segments to which the dynamometer was applied were in gravityeliminated or lessened positions. Thus, the knee actions were tested with the subjects sitting. The hip and ankle actions were tested with the JOSPT Volume 24 Number 2 August 1996

3 RESEARCH STUDY N = Newtons; D = side; ND = side. TABLE 2. Descriptive statistics for subject characteristics, strength, and gait variables. subjects supine. Test duration was of about 6-7 seconds, a second or two to come to maximal effort and 4-6 seconds of maximal effort. The peak force of each effort was recorded. Subjects were manually stabilized during all test$. Statistical Analysis The Systat statistical program (Systat Inc., Evanston, IL) was used Variable Comfortable speed Maximum speed Gender -.254* -.390t Weight Height.226*.293t Age * Significant at p <.0J. t Significant at p <.001. TABLE 3. Pearson correlations between-subject characteristics and walking speed. for all descriptive and inferential analyses (35). Intraclass correlation coefficients (equation 3.1) were first calculated to verify the reliability of the gait speed measures (comfortable =.882, maximum =.907) (32). Thereafter, the mean of the two trials at each speed was used in all analyses. The mean of the two peak force measurements was used to describe the strength of each muscle action. Both this value (actual force) and the actual force divided by body weight (normalized force) were used in inferential analysis. Inferential analysis of the relationships between independent variables and gait speed involved Pearson product moment correlations and multiple regression. As numerous inferential procedures were performed, a probability level of p 5.O1 was selected as critical. RESULTS Table 2 indicates the gait speed and lower extremity muscle strength data by gender. Table 3 presents the Pearson correlations between-subject characteristics and gait speed. Gender and height were correlated significantly with gait speed but weight and age were not. The variance in either comfortable or maximum gait speed explained by any one of the subject characteristics was small (< 16.0%). Table 4 lists the correlations between the strength of each of the five lower extremity muscle actions and the gait speeds. The correlations, which were all higher with maximum than with comfortable speed, ranged from.073 to 372. Strength normalized to body weight typically correlated more highly with gait speed than strength not so normalized. Only the correlations between ankle dorsiflexion strength and gait speed were consistently insignificant. Regression analysis (Table 5). into which the four subject characteristics and five (nonnormalized) strength measures were entered, showed gender, body weight, and nondominant hip flexion strength to be the best set of independent predictors of both comfortable and maximum gait speed. Although highly significant, the multiple correlations associated with the regression equations explained a very limited percentage of the variance in gait speed (1 3.1 % comfortable, 21.1 % maximum). DISCUSSION This study presents reference values for gait speed that should be useful to clinicians making judgements about the gait performance of patient. measured with a stopwatch over short distances indoors. The comfortable gait speeds reported in this study are faster than most of the gait speeds described in the studies summarized in Table 1. The mean values for comfortable speed listed in Table 1, however, are generally with- Volume 24 Number 2 * August 1996 *JOSPT

4 RESEARCH STUDY Musde Adion Side Measurement* Comfortable Swed Maximum Swed Hip flexion A.277$.343* Hip abduction Knee flexion Knee extension Ankle dorsiflexion * A = Actual force; N = Normalized force (actual forcelbody weight). t Correlations significant at p <.01. * Correlations significant at p <.001. TABLE 4. Pearson correlations between lower extremity muscle action strengths and walking speed* in two standard deviations of those in this study. The comfortable speed of most of the subjects in this study falls into what Smidt categorized as "moderate" or "moderate-fast" forward walking velocity (33). In addition to comfortable speed values, this study reports maximum gait speed values. Although some researchers have recognized the importance of maximum gait speed (33). the available literature does not provide many values to which the norms of this study can be compared. The maximum speed of most subjects in this study fits into the "fast" or "very fast" categories described by Smidt (33). The values reported here can be useful, nevertheless, as a standard to which the gait of elderly individuals can be compared. Granting that maximum speed is prob ably not emphasized in many clinical settings, such speed may be required of some elderly individuals if they are to safely cross streets in the time allotted to them (10,15,29). The results of the correlation and regression analysis of this study provide some information useful to the formulation of reference values for clinical use. First, the analysis confirms the findings of other studies that show a relationship between gender and gait speed (13,24). Though the relationship is not strong, it is of sufficient magnitude to justify using different gait speed reference values for men and women. Second, in the restricted age range of subjects in this study, the often demonstrated Equation R R2 P Comfortable speed = G -.04W +.21S.362.I31.OOO Maximum speed = G -.08W +.21S G = Gender ( = 0, = I). W = Weight (in Newtons). S = Strength of hip flexion (in Newtons), nondominant side for comfortable speed and dominant side for maximum speed. TABLE 5. Results of regression analysis selecting the best independent predictors of gait speed from subject characteristics and lower extremity strength measures obtained from 156 adults. JOSF'T * Volume 24 * Number 2 * August 1996 relationship between age and gait speed (6.24) was not confirmed. Consequently, different reference values do not appear necessary for individuals in their sixth, seventh, or eighth decades. Third, although height was found in this study to predict gait speed (1 3), as in previous studies, the effect of height was not independent of the effect of gender. Once gender was entered into the regression equation of this study, height was not found to offer any additional significant prediction. This being the case, heightnormalized reference values for gait speed are not provided in this study. The results of this study, like those of other studies involving elderly individuals (2,6,8,9,13,16,17), demonstrate a relationship between lower extremity muscle strength and gait speed. Of course, correlations do not prove cause and effect. For the subjects of this study, the correlations between elbow flexion strength (data unreported) and comfortable (.280 and.297) and maximum (.414 and.415) gait speed were higher than those involving any of the lower extremity strength measures. Clearly, elbow flexion strength cannot cause gait speed. These facts notwithstanding, the correlations of this and other studies should not be disregarded. When individuals increase their gait speed, higher levels of muscle activity (21) and larger joint moments (36, 37) are observed. Thus, muscle force generation is essential to ambulation. Although the intensity of muscle activation required for gait is clearly sub maximal (28), individuals may adjust their gait speed based on their strength so that they are able to maintain some degree of reserve or to forestall fatigue (which is intensity related). Recent studies of individuals in their eighties and nineties have shown that they can improve their gait speed following muscle strength training (9,16). If such training is undertaken, with the goal of increasing gait speed, it might be best to direct it at actions with the highest correlations with gait speed. Hip flex-

5 RESEARCH STUDY ion may be one such action, given the results of this study and research on stroke patients (25,26). Ankle plantar flexion, not measured in this study because of the upper limits of the dynamometer and the testers' strengths, is another (25,26). The &cacy of intensive programs directed at those actions is a topic worthy of Mer research. CONCLUSION This study presents reference values for both comfortable and maximum gait speed for men and women, age years. As the values were obtained using methods that can be applied practically in a variety of settings, they should be useful to clinicians. The values differ for men and women. Also influencing the measurements are an individual's size and lower extremity muscle strength. JOSPT ACKNOWLEDGMENTS This work was supported in part by John Chatillon and Sons, Inc., Greensboro, NC. REFERENCES 1. Andrews A W, Thomas M W, Bohannon RW: Normative values for muscle strength obtained by hand-held dynamometry. 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