Perceptualand Motor Skills, 1990, 71, 123-128. O Perceptual and Motor Skills 1990
PERCEPTION OF UNILATERAL WEIGHTBEARING DURING UNILATERAL AND BILATERAL UPRIGHT STANCE ' LORI SCHAEFER AND RICHARD W. BOHANNON University of Connecticut
Summary.-To compare the effect of stance (unilateral vs bilateral) and of weightbearing target (25%, SO%, 75%) on error in weightbearing perception, two groups, unilateral and bilateral, of 30 comparable subjects were tested. Weightbearing was measured while subjects stood on digital scales; bilateral stance was accomplished using two scales, and unilateral stance was accomplished using a walker and a single scale. The subject's error in perceiving weightbearing at each target level was assessed by taking the absolute value of the target percent weightbearing minus the mean actual percent weightbearing. The mean errors at the 25, 50 and 75% targets were 6.5, 3.2, 17.6% for the unilateral group and 3.1, 1.4, 3.8% for the bilateral group. A two-way analysis of variance indicated the magnitude of error differed between groups and target levels, with a greater over-all error displayed by the unilateral weightbearing group. Our results suggest that adults are less accurate in judging weightbearing while standing on one, rather than on two, lower extremities. Clinicians should not expect patients to follow accurately instructions to weightbear at a specific percentage of full weight, particularly when using an assistive device to adjust weightbearing.
Although the symmetry of weightbearing has been examined previously with patients as well as with healthy subjects, the perception of weightbearing by healthy subjects was not addressed until Bohannon, et al.'s (1989) recent study of weightbearing perception during bilateral stance. I n that study, subjects were required to adjust their weightbearing to what they perceived to be 25, 50, and 75% of their weight through a randomly designated lower extremity. Measurements were taken with each foot on a digital scale. The study showed that the 50% weightbearing target was the most accurately approximated. That result may have an explanation. With both feet on the ground 50% weightbearing on one side results from symmetrical weightbearing, which may be easier to judge than various degrees of asymmetrical weightbearing. Another study, not focused on perception per se but relevant to perception of weightbearing, was performed by Warren and Lehmann (1975). Their study showed that during weightbearing training with biofeedback and after training, subjects often exceeded target loads by 50% or more. As neither of the aforementioned studies examined perception of unilateral weightbearing during unilateral stance, further research is necessary before physicians or therapists can make informed judgments about the abil-
'Address correspondence to R. W. Bohannon, PT., Ed.D., School of Allied Health, U-101, University of Connecticut, Storrs, CT 06269-2101.
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L. SCHAEFER & R. W. BOHANNON
ity of patients to cornply with weightbearing restrictions. The purpose of this study was to compare the effect of stance condition and weightbearing target on error in perception of weightbearing.
The subjects were volunteers who provided informed consent. The criterion for selection was that subjects had no known orthopedic or neurological problems. The unilateral and bilateral weightbearing groups each consisted of 30 subjects; 18 men and 12 women in the unilateral group, and 16 men and 14 women in the bilateral group. See Table 1 for the mean, range and standard deviations of age, height and weight for each group. TABLE 1 WNS, STANDARD DEVIATIONS, AND RANGES FORAGE,HEIGHT, AND WEIGHT OF HEALTHY SUBJECTS WHOSEUNILATERAL W E I G H T E WAS I~G TESTEDDURING EITHER UNILATERAL OR BILATERN STANCE (ns = 30) Group
M Unilateral Bilateral
28.5 33.0
Age (yr.) SD Range 7.7 7.9
20-46 22-46
M 172.3 170.8
Height (cml SD Range 9.6 10.0
150-188 150-188
Weight (kg)
M
SD
Range
70.0 73.1
12.1 15.1
50- 96 47-105
The scales used in the study were digital Borg Electronic Scales that registered weight in pounds to the nearest .I pound. The scales were c&brated prior to each testing session. One scale and a standard walker, adjusted for each subject; were used during the unilateral weightbearing condition. For the bilateral weightbearing condition, subjects would step on two scales, with the left and right foot each placed in the middle of one scale. Prior to participating, information was recorded on the subjects' age, height, weight, sex, and dominant lower extremity (leg used to kick a ball). Moreover, the tested lower extremity was randomly selected by a coin toss. For the unilateral weightbearing group the dominant lower extremities of 12 subjects were tested. For the bilateral weightbearing group the dominant lower extremities of 18 subjects were tested. For both groups, the testing was done with shoes removed and subjects looking straight ahead. The subjects were told that after stepping onto the scale(s), they would be asked to adjust their weight, through the selected lower extremity, to each of three randomly ordered target levels-25, 50 and 75% of their total body weight. I t was explained that they would be allowed three attempts at each target level but would not be given feedback. To provide subjects with an idea of weightbearing targets, the bilateral stance group was told that, if they were to stand symmetrically on two legs, each leg would be bearing 50% of their total body weight. It was also explained that, were they to bear 25% of the weight through a designated
PERCEPTION OF KIEIGHTBEARING
125
lower extremity, 75% of their weight would be borne through the opposite leg. The subjects of the unilateral stance group were told that, if 50% of the body weight was on the designated lower extremity, then 50% would be supported by the upper extremities and the walker. Additionally, if 25% of their weight was borne through a single lower extremity, 75% of the body weight would be supported by the hands on the walker.
FIG. 1. An individual demonstrating how weightbearing was measured for the unilateral stance condition
For each target level (25, 50, 75%) subjects were told to step onto the scale placing the foot of the leg to be tested in the center of the scale. Subjects in the bilateral group placed the opposite foot on the center of a second scale whereas the subjects in the unilateral group held the opposite lower extremity off of the ground (Fig. 1). Subjects were asked to adjust their weight as quickly and accurately as possible to the specified target level. Once this adjustment had been made, the subject notified the investigator who then counted to four (at a rate of one count per second) and took
126
L. SCHAEFER & R. W. B O H A N N O N
the reading present on the scale. Subjects remained on the scale during a 10-sec. rest between the three trials at each target level. During the rest period, the unilateral group was permitted to stand on both legs and the bilateral group was allowed to stand comfortably. Between a set of trials at each target level, the subjects stepped off of the scale (s) for several seconds. Each weightbearing measurement was divided by total body weight to yield the actual percentage of weightbearing for each trial at the three target levels. A one-way analysis of variance for repeated measures was applied to the t h e trial measures at each target level and an intraclass correlation coefficient calculated to judge whether the weightbearing measurements were reliable enough to justify using the mean of each subject's three trials at each target-weightbearing level. The intraclass correlation coefficients for the unilateral weightbearing group were for the 25% target = .737, the 50% target = .844, and the 75% target = .834. The intraclass correlation coeff~clentsfor the bilateral weightbearing group were for the 25% target = .901, the 50% target = ,933, and the 75% target = .877. As the intraclass correlation coefficients were of sufficient magnitude (greater than .700), we used the mean actual percent weightbearing for each weightbearing target level (calculated for each subject from the three trials). Etrors in perception of weightbearing were calculated for each subject by taking the absolute value of the difference between the mean percent of actual weightbearing and the associated percent of target-level weightbearing. For example, if a subject's mean percent actual weightbearing at the 25% target was 29.0%, then the error was 4.0% The effects of groups (unilateral, bilateral) and target level (25, 50, 75%) on error in perception of weightbearing, were examined by using a two-way mixed model analysis of variance.
RESULTS Fig. 2 summarizes the actual percent weightbearing by the subjects in the unilateral and bilateral groups during three trials at each weightbearing target (25%, 50%, 75%). The means, standard deviations, and ranges of the mean percent actual weightbearing a t the 25, 50, and 75% target levels, respectively, were for the unilateral group 31.5f 9.5 (14.0-57.7), and 46.8k9.6 (30.9-74.9), 57.4+ 11.4 (34.8-85.9) and for the bilateral group-28.1 f 8.5 (11.9-45.1), 51.4 5.4 (43.9-70.1), and 71.2 & 8.7 (56.9-88.0). The means, standard deviations, and ranges of the absolute errors (in percent) in perception of weightbearing at the 25, 50 and 75% target levels, respectively, were 9.2 & 6.6 (.33-32.70), 8.0 + 6.0 (.lo-24.87), 18.5k9.7 (1.3-40.2) for the unilateral group and 7.3k5.2 (.I-20.7), 3.6k4.2 (.0-20.1), 8.1 f 5 . 1 (.4-18.1) for the bilateral group. Table 2 presents the results of the two-way analysis of variance cornpar-
PERCEPTION O F WEIGHTBEARING
50
25
75
TARGET WEIGHTBEARING (70)
FIG2. Means and standard deviations for actual weightbearin durin three trials at each of three targets. Values are from a group of subjects measured whfe weig!tbearing unilaterally and a group of subjects measured while weightbearing bilaterally. ing the magnitude of errors between groups and targets. The analysis yielded a significant difference ( p < .001) in the error of perceived weightbearing between groups. The analysis also gave a significant difference ( p = .02) in the error of perceived weightbearing between targets. TABLE 2 TWO-WAY ANALYSIS OF VARIANCE COMPARING ERRORS INUNILATERALWEIGHTBEARING PERCEPTION BETWEENWEIGHTBEARING GROUPS (UNLLATERAL vs BILATERAL) AND WEIGHTBEARING TARGETS (25, 50, AND 75%) Source
SS
df
MS
F
Groups Error Targets Error
1398.5 2452.8 350.5 4740.5
1 58 2 116
1398.5 42.3 175.2 40.9
33.1
P < .001
4.3
< .02
DISCUSSION Over-all, subjects in each group had trouble judging weightbearing for each of the three targets. Following the trials performed by each subject, many individuals reported that they had great difficulty estimating the required amounts and were unsure of the accuracy of their estimation. At each of the selected target-weightbearing levels, the actual percent weightbearing for the bilateral stance group was more accurate (closer to
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L. SCHAEFER & R. W. BOHANNON
the target) than for the unilateral stance group. The scores on trials closest to the target percent were given by the bilateral stance group at the 50% weightbearing target. This may be because individuals in the bilateral group were able to use the contralateral lower extremity ( u d k e the unilateral stance group) to assist in making their judgements about weightbearing. The target of 50% weightbearing required individuals to distribute their weight equally through both lower extremities. Equality may be more easily estimated than inequality. Consistent with this idea above, the intraclass correlation (reliability)- coefficients indicated that subjects in the unilateral stance group were less consistent than the subjects in the bilateral stance group in their repeated attempts at the three target levels. These findings are important to clinicians, whether dealing with the orthopedic patient (e.g., fractures) or neurologic patient (e.g., stroke) for whom decreasing or increasing weightbearing through one of the lower extremities is a goal. The clinician cannot assume, based on these findings with healthy subjects, that patients can accurately judge weightbearing at the three target levels tested. Whether compensating for the weight on one designated lower extremity by using both hands on a walker or by using the contralateral lower extremity, the subjects' accuracy was too poor to justify use of instructions for specific percentages of weightbearing in the clinic. Perception of weightbearing percent may be more difficult during a dynamic activity, such as gait, than in this study. Here adequate time was given for subjects to adjust their weight to each specific target of static weightbearing. I n gait, this adjustment would have to be made spontaneously and repeatedly commencing with heel strike. Instructions for specific percentages of weightbearing may be particularly problematic for patients who are walking. The results of Warren and Lehmann (1975) suggest this to be the case. The accuracy of perception of weightbearing during gait merits further investigation. Also worthy of study are the effects of feedback on judgement of weightbearing. With feedback, the ability of individuals to judge weightbearing may improve. REFERENCES BOHANNON, R. W., WATERS,G., & COOPER, J. (1989) Perception of unilateral lower extremity weightbearing during bilateral upright stance. Perceptual and Motor Skillr, 69, 875-880. & LEHMANN, J. (1975) Training procedures and biofeedback methods to achieve controlled partial weightbearing: an assessment. Archives of Physical Medicine and Rehabilitution, 56, 449-455.
WARREN,G.,
Accepted June 20, 1990.
PERCEPTION OF UNILATERAL WEIGHTBEARING DURING UNILATERAL AND BILATERAL UPRIGHT STANCE ' LORI SCHAEFER AND RICHARD W. BOHANNON University of Connecticut
Summary.-To compare the effect of stance (unilateral vs bilateral) and of weightbearing target (25%, SO%, 75%) on error in weightbearing perception, two groups, unilateral and bilateral, of 30 comparable subjects were tested. Weightbearing was measured while subjects stood on digital scales; bilateral stance was accomplished using two scales, and unilateral stance was accomplished using a walker and a single scale. The subject's error in perceiving weightbearing at each target level was assessed by taking the absolute value of the target percent weightbearing minus the mean actual percent weightbearing. The mean errors at the 25, 50 and 75% targets were 6.5, 3.2, 17.6% for the unilateral group and 3.1, 1.4, 3.8% for the bilateral group. A two-way analysis of variance indicated the magnitude of error differed between groups and target levels, with a greater over-all error displayed by the unilateral weightbearing group. Our results suggest that adults are less accurate in judging weightbearing while standing on one, rather than on two, lower extremities. Clinicians should not expect patients to follow accurately instructions to weightbear at a specific percentage of full weight, particularly when using an assistive device to adjust weightbearing.
Although the symmetry of weightbearing has been examined previously with patients as well as with healthy subjects, the perception of weightbearing by healthy subjects was not addressed until Bohannon, et al.'s (1989) recent study of weightbearing perception during bilateral stance. I n that study, subjects were required to adjust their weightbearing to what they perceived to be 25, 50, and 75% of their weight through a randomly designated lower extremity. Measurements were taken with each foot on a digital scale. The study showed that the 50% weightbearing target was the most accurately approximated. That result may have an explanation. With both feet on the ground 50% weightbearing on one side results from symmetrical weightbearing, which may be easier to judge than various degrees of asymmetrical weightbearing. Another study, not focused on perception per se but relevant to perception of weightbearing, was performed by Warren and Lehmann (1975). Their study showed that during weightbearing training with biofeedback and after training, subjects often exceeded target loads by 50% or more. As neither of the aforementioned studies examined perception of unilateral weightbearing during unilateral stance, further research is necessary before physicians or therapists can make informed judgments about the abil-
'Address correspondence to R. W. Bohannon, PT., Ed.D., School of Allied Health, U-101, University of Connecticut, Storrs, CT 06269-2101.
124
L. SCHAEFER & R. W. BOHANNON
ity of patients to cornply with weightbearing restrictions. The purpose of this study was to compare the effect of stance condition and weightbearing target on error in perception of weightbearing.
The subjects were volunteers who provided informed consent. The criterion for selection was that subjects had no known orthopedic or neurological problems. The unilateral and bilateral weightbearing groups each consisted of 30 subjects; 18 men and 12 women in the unilateral group, and 16 men and 14 women in the bilateral group. See Table 1 for the mean, range and standard deviations of age, height and weight for each group. TABLE 1 WNS, STANDARD DEVIATIONS, AND RANGES FORAGE,HEIGHT, AND WEIGHT OF HEALTHY SUBJECTS WHOSEUNILATERAL W E I G H T E WAS I~G TESTEDDURING EITHER UNILATERAL OR BILATERN STANCE (ns = 30) Group
M Unilateral Bilateral
28.5 33.0
Age (yr.) SD Range 7.7 7.9
20-46 22-46
M 172.3 170.8
Height (cml SD Range 9.6 10.0
150-188 150-188
Weight (kg)
M
SD
Range
70.0 73.1
12.1 15.1
50- 96 47-105
The scales used in the study were digital Borg Electronic Scales that registered weight in pounds to the nearest .I pound. The scales were c&brated prior to each testing session. One scale and a standard walker, adjusted for each subject; were used during the unilateral weightbearing condition. For the bilateral weightbearing condition, subjects would step on two scales, with the left and right foot each placed in the middle of one scale. Prior to participating, information was recorded on the subjects' age, height, weight, sex, and dominant lower extremity (leg used to kick a ball). Moreover, the tested lower extremity was randomly selected by a coin toss. For the unilateral weightbearing group the dominant lower extremities of 12 subjects were tested. For the bilateral weightbearing group the dominant lower extremities of 18 subjects were tested. For both groups, the testing was done with shoes removed and subjects looking straight ahead. The subjects were told that after stepping onto the scale(s), they would be asked to adjust their weight, through the selected lower extremity, to each of three randomly ordered target levels-25, 50 and 75% of their total body weight. I t was explained that they would be allowed three attempts at each target level but would not be given feedback. To provide subjects with an idea of weightbearing targets, the bilateral stance group was told that, if they were to stand symmetrically on two legs, each leg would be bearing 50% of their total body weight. It was also explained that, were they to bear 25% of the weight through a designated
PERCEPTION OF KIEIGHTBEARING
125
lower extremity, 75% of their weight would be borne through the opposite leg. The subjects of the unilateral stance group were told that, if 50% of the body weight was on the designated lower extremity, then 50% would be supported by the upper extremities and the walker. Additionally, if 25% of their weight was borne through a single lower extremity, 75% of the body weight would be supported by the hands on the walker.
FIG. 1. An individual demonstrating how weightbearing was measured for the unilateral stance condition
For each target level (25, 50, 75%) subjects were told to step onto the scale placing the foot of the leg to be tested in the center of the scale. Subjects in the bilateral group placed the opposite foot on the center of a second scale whereas the subjects in the unilateral group held the opposite lower extremity off of the ground (Fig. 1). Subjects were asked to adjust their weight as quickly and accurately as possible to the specified target level. Once this adjustment had been made, the subject notified the investigator who then counted to four (at a rate of one count per second) and took
126
L. SCHAEFER & R. W. B O H A N N O N
the reading present on the scale. Subjects remained on the scale during a 10-sec. rest between the three trials at each target level. During the rest period, the unilateral group was permitted to stand on both legs and the bilateral group was allowed to stand comfortably. Between a set of trials at each target level, the subjects stepped off of the scale (s) for several seconds. Each weightbearing measurement was divided by total body weight to yield the actual percentage of weightbearing for each trial at the three target levels. A one-way analysis of variance for repeated measures was applied to the t h e trial measures at each target level and an intraclass correlation coefficient calculated to judge whether the weightbearing measurements were reliable enough to justify using the mean of each subject's three trials at each target-weightbearing level. The intraclass correlation coefficients for the unilateral weightbearing group were for the 25% target = .737, the 50% target = .844, and the 75% target = .834. The intraclass correlation coeff~clentsfor the bilateral weightbearing group were for the 25% target = .901, the 50% target = ,933, and the 75% target = .877. As the intraclass correlation coefficients were of sufficient magnitude (greater than .700), we used the mean actual percent weightbearing for each weightbearing target level (calculated for each subject from the three trials). Etrors in perception of weightbearing were calculated for each subject by taking the absolute value of the difference between the mean percent of actual weightbearing and the associated percent of target-level weightbearing. For example, if a subject's mean percent actual weightbearing at the 25% target was 29.0%, then the error was 4.0% The effects of groups (unilateral, bilateral) and target level (25, 50, 75%) on error in perception of weightbearing, were examined by using a two-way mixed model analysis of variance.
RESULTS Fig. 2 summarizes the actual percent weightbearing by the subjects in the unilateral and bilateral groups during three trials at each weightbearing target (25%, 50%, 75%). The means, standard deviations, and ranges of the mean percent actual weightbearing a t the 25, 50, and 75% target levels, respectively, were for the unilateral group 31.5f 9.5 (14.0-57.7), and 46.8k9.6 (30.9-74.9), 57.4+ 11.4 (34.8-85.9) and for the bilateral group-28.1 f 8.5 (11.9-45.1), 51.4 5.4 (43.9-70.1), and 71.2 & 8.7 (56.9-88.0). The means, standard deviations, and ranges of the absolute errors (in percent) in perception of weightbearing at the 25, 50 and 75% target levels, respectively, were 9.2 & 6.6 (.33-32.70), 8.0 + 6.0 (.lo-24.87), 18.5k9.7 (1.3-40.2) for the unilateral group and 7.3k5.2 (.I-20.7), 3.6k4.2 (.0-20.1), 8.1 f 5 . 1 (.4-18.1) for the bilateral group. Table 2 presents the results of the two-way analysis of variance cornpar-
PERCEPTION O F WEIGHTBEARING
50
25
75
TARGET WEIGHTBEARING (70)
FIG2. Means and standard deviations for actual weightbearin durin three trials at each of three targets. Values are from a group of subjects measured whfe weig!tbearing unilaterally and a group of subjects measured while weightbearing bilaterally. ing the magnitude of errors between groups and targets. The analysis yielded a significant difference ( p < .001) in the error of perceived weightbearing between groups. The analysis also gave a significant difference ( p = .02) in the error of perceived weightbearing between targets. TABLE 2 TWO-WAY ANALYSIS OF VARIANCE COMPARING ERRORS INUNILATERALWEIGHTBEARING PERCEPTION BETWEENWEIGHTBEARING GROUPS (UNLLATERAL vs BILATERAL) AND WEIGHTBEARING TARGETS (25, 50, AND 75%) Source
SS
df
MS
F
Groups Error Targets Error
1398.5 2452.8 350.5 4740.5
1 58 2 116
1398.5 42.3 175.2 40.9
33.1
P < .001
4.3
< .02
DISCUSSION Over-all, subjects in each group had trouble judging weightbearing for each of the three targets. Following the trials performed by each subject, many individuals reported that they had great difficulty estimating the required amounts and were unsure of the accuracy of their estimation. At each of the selected target-weightbearing levels, the actual percent weightbearing for the bilateral stance group was more accurate (closer to
128
L. SCHAEFER & R. W. BOHANNON
the target) than for the unilateral stance group. The scores on trials closest to the target percent were given by the bilateral stance group at the 50% weightbearing target. This may be because individuals in the bilateral group were able to use the contralateral lower extremity ( u d k e the unilateral stance group) to assist in making their judgements about weightbearing. The target of 50% weightbearing required individuals to distribute their weight equally through both lower extremities. Equality may be more easily estimated than inequality. Consistent with this idea above, the intraclass correlation (reliability)- coefficients indicated that subjects in the unilateral stance group were less consistent than the subjects in the bilateral stance group in their repeated attempts at the three target levels. These findings are important to clinicians, whether dealing with the orthopedic patient (e.g., fractures) or neurologic patient (e.g., stroke) for whom decreasing or increasing weightbearing through one of the lower extremities is a goal. The clinician cannot assume, based on these findings with healthy subjects, that patients can accurately judge weightbearing at the three target levels tested. Whether compensating for the weight on one designated lower extremity by using both hands on a walker or by using the contralateral lower extremity, the subjects' accuracy was too poor to justify use of instructions for specific percentages of weightbearing in the clinic. Perception of weightbearing percent may be more difficult during a dynamic activity, such as gait, than in this study. Here adequate time was given for subjects to adjust their weight to each specific target of static weightbearing. I n gait, this adjustment would have to be made spontaneously and repeatedly commencing with heel strike. Instructions for specific percentages of weightbearing may be particularly problematic for patients who are walking. The results of Warren and Lehmann (1975) suggest this to be the case. The accuracy of perception of weightbearing during gait merits further investigation. Also worthy of study are the effects of feedback on judgement of weightbearing. With feedback, the ability of individuals to judge weightbearing may improve. REFERENCES BOHANNON, R. W., WATERS,G., & COOPER, J. (1989) Perception of unilateral lower extremity weightbearing during bilateral upright stance. Perceptual and Motor Skillr, 69, 875-880. & LEHMANN, J. (1975) Training procedures and biofeedback methods to achieve controlled partial weightbearing: an assessment. Archives of Physical Medicine and Rehabilitution, 56, 449-455.
WARREN,G.,
Accepted June 20, 1990.
