http://informahealthcare.com/ptp ISSN: 0959-3985 (print), 1532-5040 (electronic) Physiother Theory Pract, 2015; 31(2): 146–152 ! 2015 Informa Healthcare USA, Inc. DOI: 10.3109/09593985.2014.960539

CLINICAL TECHNICAL NOTE

Reliability of measurements of hip abduction strength obtained with a hand-held dynamometer Akira Ieiri, PhD, RPT1, Eiki Tushima, PhD, RPT2, Kazuhiro Ishida, PhD, RPT1, Masahiro Inoue, PhD, MD3, Taiki Kanno, PhD, MD3, and Takeshi Masuda, PhD, MD3

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1

Department of Rehabilitation, Eniwa Hospital, Eniwa City, Hokkaido, Japan, 2Graduate School of Health Sciences, Hirosaki University, Hirosaki, Aomori, Japan, and 3Department of Orthopedic Surgery, Eniwa Hospital, Eniwa City, Hokkaido, Japan

Abstract

Keywords

This study aimed to evaluate intrarater and interrater reliability when measuring hip abductor strength in the supine position using a hand-held dynamometer (HHD) (Study 1), and to elucidate the relationships between measured values and examiners’ physical characteristics (Study 2). Three healthy examiners (1 female, 24 y.o. and 2 males 23 and 27 y.o) and 12 subjects (6 females, 24.5 ± 2.8 years and 6 males, 27.7 ± 3.5 years) participated in Study 1, and 20 healthy examiners (7 females, 22.3 ± 1.3 years and 13 males, 29.4 ± 8.2 years) and 2 subjects (1 female, 24 y.o. and 1 male 27 y.o) participated in Study 2. All healthy examiners were hospital employees. Hip abductor strength was measured by HHD with hand fixation and with belt fixation, and examiner age, sex, height, weight, BMI, and dominant hand grip strength were evaluated. The intraclass correlation coefficient (ICC) (1,1), a measure of intrarater reliability, was 0.89–0.95 with hand fixation and 0.96–0.97 with belt fixation. ICC (2,1), a measure of interrater reliability, was 0.76–0.79 and 0.90–0.93, respectively. In subjects with high muscle strength (the examiner’s hand was moved), the examiner’s dominant hand grip strength affected muscle strength values with hand fixation (standardized partial regression coefficient ¼ 0.78, determination coefficient R2 ¼ 0.61, p50.01). In subjects with low muscle strength (the examiner’s hand was not moved), no variables had effect. When the muscle strength of the subject is weak, both methods can be used. When the muscle strength of the subject is strong, it is necessary to adjust the value obtained by the examiner’s dominant hand grip strength in the hand fixation method.

Belt fixation, hand fixation, handheld dynamometer, hip abductor muscle strength, supine position

Introduction Methods used to measure hip abductor muscle strength include manual muscle testing (MMT) (Sasaji, Horaguchi, Yamada, and Iwai, 2012); isokinetic devices (Asayama et al, 2005; Cahalan, Johnson, Liu, and Chao, 1989; Downing et al, 2001; Jacobs et al, 2005; Kendall, Schmidt, and Ferber, 2010; Unlu et al, 2007); and handheld dynamometers (HHDs) (Arnold, Warkentin, Chilibeck, and Magnus, 2010; Bohannon, 1986; Bouffard et al, 2011; Click Fenter, Bellew, Pitts, and Kay, 2003; Ireland, Willson, Ballantyne, and Davis, 2003; Kelln, McKeon, Gontkof, and Hertel, 2008; Kiyama, Naito, Shinoda, and Maeyama, 2010; Krause et al, 2007; Rutherford and Hubley-Kozey, 2009; Singh and Lewallen, 2013; Thorborg et al, 2013; Vanpee et al, 2011; Widler et al, 2009; Youdas et al, 2008). Of these measurement methods, MMT is the most convenient and practical, but because it is a subjective assessment, its reliability is low with a high MMT score (Frese, Brown, and Norton, 1987; Sapega, 1990). Since isokinetic devices require time for measurement, and they are not portable, they are not practical for use in clinical settings where rapid assessment is necessary. Moreover, isokinetic devices Address correspondence to Akira Ieiri, Department of Rehabilitation, Eniwa Hospital, 1-1 Kogane-chuo-2-chome, Eniwa City, Hokkaido 0611449, Japan. E-mail: [email protected]

History Received 31 October 2013 Revised 25 June 2014 Accepted 29 June 2014 Published online 25 September 2014

are expensive to set up (Hartmann, Knols, Murer, and de Bruin, 2009). On the other hand, measurement with a HHD is just as convenient as MMT, and objective assessment is also possible. In addition, a HHD is less expensive than an isokinetic device and convenient for use as a portable instrument (Maffiuletti, 2010). Reports of measurements of hip abductor muscle strength with a HHD recommend that patients be in a side-lying position (Widler et al, 2009), and differences in measured values due to differences in upper extremity muscle strength of examiners have been described (Thorborg et al, 2013). However, because patients in the early postoperative period cannot assume a side-lying position, measurements are often not performed in this position. Moreover, individual differences in upper extremity muscle strength exist among examiners, who must stabilize (fixate) the HHD during measurement. Furthermore, side-lying is affected by gravity (Andrews, Thomas, and Bohannon, 1996). Measurement of hip abductor muscle strength starting early after surgery may be an important factor in assessing functional prognosis. However, this has not been implemented because there have been only brief reports (Andrews, Thomas, and Bohannon, 1996; Traina et al, 2010), and evaluation of measurement methods in the supine position has seldom been reported. Therefore, if reliability of measurement methods in the supine position can be established, and if measured values can be adjusted based on the upper extremity muscle strength of

Hip abductor strength in HHD

DOI: 10.3109/09593985.2014.960539

Table 1. Characteristics of Study 1 participants.

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Sex Examiner (n ¼ 3) A Male B Male C Female Mean – SD – Subjects (n ¼ 12) a Male b Male c Male d Male e Male f Male g Female h Female i Female j Female k Female l Female Mean – SD –

Age

Height (m)

Weight (kg)

147

Table 2. Characteristics of Study 2 participants. BMI (kg/m2)

27 23 24 24.7 2.1

1.77 1.60 1.60 1.66 0.10

74 51 52 59 13

23.6 19.9 20.3 21.3 2.0

26 30 26 29 33 22 26 27 28 20 23 23 26.1 3.7

1.72 1.68 1.67 1.63 1.67 1.73 1.54 1.55 1.53 1.53 1.50 1.63 1.62 0.08

76 56 50 58 58 69 42 46 43 41 40 52 52.6 11.4

25.7 19.8 17.9 22.0 20.8 23.1 17.7 19.1 18.4 17.5 17.8 19.6 19.9 2.5

SD, standard deviation.

examiners, then the process of muscle strength recovery starting early after surgery can be assessed quantitatively. This can provide useful data in the postoperative rehabilitation process. In the present study, the aim was to evaluate reliability when measuring hip abductor muscle strength in the supine position using a HHD. The relationship between the measured values and the physical characteristics of the examiners, such as their upper extremity muscle strength, was also evaluated. This study consisted of two parts. In Study 1, a HHD was used to measure hip abductor muscle strength in the supine position. Measurements were made under two conditions: (1) hand fixation of the HHD and (2) belt fixation of the HHD. Then, intrarater and interrater reliabilities were evaluated. In Study 2, it was determined whether upper extremity muscle strength and other physical characteristics of the examiners affected the hip abductor muscle strength values measured with hand fixation and HHD.

Methods This study was conducted in accordance with the Declaration of Helsinki, and subjects’ consent was obtained on admission after they were given a full explanation of the purpose and objectives of the study, the voluntary nature of their participation in the study, their freedom to withdraw at any time, and the measures taken to ensure the protection of their privacy (Hirosaki University Graduate School of Medicine Ethics Committee, approval no. 2012-150). Participants Study 1 included 3 healthy examiners who were employees (physical therapists) at our hospital and 12 subjects (Table 1). Study 2 included 20 healthy examiners who were employees at our hospital and 2 subjects (Table 2). The Declaration of Helsinki was duly considered in dealing with participants. Clinical outcomes Outcome measures included hip abductor muscle strength and examiner age, sex, height, weight, BMI, and dominant hand grip strength. Hip abductor muscle strength was measured using hand fixation of the HHD and belt fixation of the HHD. In Study 2, the

Sex Examiner (n ¼ 20) 1 Male 2 Male 3 Male 4 Male 5 Male 6 Male 7 Male 8 Male 9 Male 10 Male 11 Male 12 Male 13 Male 14 Female 15 Female 16 Female 17 Female 18 Female 19 Female 20 Female Mean – SD – Subjects (n ¼ 2) (1) Male (2) Female Mean – SD –

Age

Height (m)

Weight (kg)

BMI (kg/m2)

Hand gripstrength (kg)

26 29 22 27 37 37 31 23 21 22 51 23 33 24 23 23 22 20 21 23 26.9 7.7

1.67 1.63 1.73 1.72 1.80 1.72 1.76 1.75 1.72 1.70 1.70 1.60 1.67 1.60 1.50 1.63 1.63 1.51 1.62 1.54 1.66 0.08

50 58 69 78 74 73 64 65 60 95 66 51 58 52 40 52 56 41 46 50 59.9 13.5

17.9 22.0 23.1 26.4 22.8 24.7 20.7 21.2 20.3 32.9 22.8 19.9 20.8 20.3 17.8 19.6 21.1 18.0 17.5 21.1 21.5 3.5

30 51 48 45 61 60 52 55 48 55 45 48 52 37 33 34 30 27 30 32 43.7 11.0

27 20 23.5 4.9

1.77 1.53 1.65 0.17

74 41 57.5 23.3

23.6 17.5 20.6 4.3

59 22 40.5 26.2

SD, standard deviation.

hip abductor muscle strength values were used based on hand fixation of the HHD.

Measurement of hip abductor muscle strength The HHD used was a Power Track II TM Commander (Nihon Medix, Matsudo, Japan). The HHD was placed such that the lower end of the sensor was located laterally to the knee joint space. For measurement with hand fixation, subjects were in the supine position, both arms were placed with 45 shoulder abduction, the hip on the test side was placed in a neutral position, and the non-tested hip was placed in maximum abduction to eliminate any contralateral force exerted during abduction motion as much as possible (Figure 1). The heel of the leg on the test side was suspended in a sling 5 cm from the floor surface to avoid friction force. Examiners positioned themselves on their hands and knees for measurement. Then, the hand holding the HHD was pressed against the examiner’s thigh near the test leg of the subject, and the other arm was placed on the side of the pelvis to stabilize the subject’s pelvis with the examiner’s forearm. If the examiner’s arm moved during measurement, a non-slip mat was placed on the floor, and the arm was placed on this mat. Examiners were careful not to press the HHD backward in the direction of hip adduction of the subject, not to allow pelvic inclination, and not to allow compensatory flexion or rotation of the subject’s hip. For measurement with belt fixation, subjects were also in the supine position, both arms were placed with 45 shoulder abduction, the HHD was positioned similarly as with hand fixation, and both hips were stabilized in the neutral position using a fixation belt (Figure 2). If the subject complained of femoral pain during testing, a towel was placed between the HHD

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: Posion of handheld dynamometer : Force of subject Figure 1. Measurement of hip abductor muscle strength (hand fixation). Subjects are in the supine position, with both arms placed with 45 shoulder abduction, the hip on the test side placed in a neutral position, and the non-tested hip placed in maximum abduction. The heel of the leg on the test side is suspended in a sling 5 cm from the floor surface.

: Posion of handheld dynamometer : Force of subject Figure 2. Measurement of hip abductor muscle strength (belt fixation). Subjects are also in the supine position, with both arms placed with 45 shoulder abduction and both hips stabilized in the neutral position using a fixation belt.

sensor and thigh. Care was also taken to prevent any compensatory motion.

subjects). Measurements were performed three times after two practice runs.

Study 1

Study 2

In Study 1, intrarater and interrater reliabilities of measurement with hand fixation and belt fixation were evaluated. The measurement sequence was planned beforehand to minimize bias. For example, measurements by hand fixation in subject 1 were made in order by examiners A–B–C, then measurements by belt fixation were made in the same order. Measurements were then similarly performed in orders of A–C–B, B–A–C, B–C–A, C–A–B, and C–B–A. Measurements were made in all six ways by three examiners. After measurement of the six subjects, the order of measurement by hand fixation and belt fixation was reversed, and testing was performed in six more subjects (total of 12

In Study 2, the relationships between hip abductor muscle strength values when measured with hand fixation and examiner age, sex, height, weight, BMI, and dominant hand grip strength were analyzed. The measurement sequence was assessment of muscle strength by 10 examiners in the one male subject, followed by measurement in the one female subject. Then, the remaining 10 examiners measured muscle strength in the one female subject, followed by measurement in the one male subject. Measured values were determined by the same method as in Study 1. The means of three measured values were used as the data.

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Table 3. Measurement of hip abductor muscle strength of Study 1 (Units: N).

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Subjects

Hand fixation Examiners A A A B B B C C C Mean SD Belt fixation Examiners A A A B B B C C C Mean SD p*

a

b

c

d

e

f

g

h

i

j

k

l

129 116 138 147 112 147 134 121 103 127.4 15.5

193 177 182 182 184 176 151 169 151 173.9 14.5

156 143 151 156 138 140 129 121 112 138.4 15.4

180 169 193 193 149 162 140 129 132 160.8 24.8

178 191 176 187 183 160 169 165 158 174.1 11.8

220 211 193 191 198 191 173 171 165 190.3 18.3

132 143 132 121 136 125 92 86 95 118.0 21.3

101 97 101 88 92 90 87 81 75 90.3 8.7

143 147 143 140 147 138 125 121 127 136.8 9.9

92 90 88 97 92 91 79 73 86 87.6 7.5

154 171 156 154 140 145 123 118 136 144.1 16.8

162 149 149 145 138 132 125 132 132 140.4 11.7

202 180 200 182 189 173 198 215 215 194.9 15.0 50.01

257 253 257 233 233 231 237 237 224 242.3 11.4 50.01

140 149 151 149 127 127 140 132 123 137.6 10.7 NS

193 204 231 213 220 220 242 264 253 226.7 23.1 50.01

198 193 220 191 211 202 209 231 222 208.6 13.8 50.01

198 206 213 191 210 193 180 209 198 199.8 10.7 NS

162 162 175 171 167 169 184 167 165 169.1 7.0 50.01

92 96 90 95 97 95 86 79 79 89.9 7.0 NS

185 187 182 167 160 176 189 182 182 178.9 9.6 50.01

132 140 129 136 132 129 136 132 136 133.6 3.7 50.01

202 200 193 206 187 198 202 213 193 199.3 7.7 50.01

158 154 145 173 169 165 160 160 165 161.0 8.3 50.01

SD, standard deviation; NS, not significant. *t-Test: Hand fixation versus belt fixation.

The interval between muscle strength measurement in each study was long enough so that subjects did not complain of being fatigued. Adequate break time was allowed in each study. Statistical analysis Study 1 To evaluate intrarater and interrater reliabilities of measurement with hand fixation and belt fixation in Study 1, intraclass correlation coefficients (ICC), standard error of the mean (SEM), and minimal detectable change (MDC) were calculated. Differences in correlation coefficients were also examined. ICC (1,1) examined intrarater reliability and ICC (2,1) examined interrater reliability of one measurement. Moreover, since the average of three measurements was used in our institution in many cases, ICC (1,3) and ICC (2,3) were also evaluated. SEM and MDC were investigated in order to show absolute reliability. When the measured value was below MDC, it was based on the error of measurement. Study 2 In Study 2, to examine whether any variables had an effect on hip abductor muscle strength when measured with hand fixation, multiple regression analysis was performed with hip abductor muscle strength as the dependent variable, and examiner age, sex, height, weight, BMI, and dominant hand grip strength as the independent variables. The measured value was taken as ICC (2,3). A correlation matrix table was examined, and the absence of multicollinearity was confirmed beforehand. The data were compiled and analyzed using R2.8.1 (CRAN: freeware; http:// www.r-project.org/) and accompanying software packages.

Results Study 1 Measured values are shown in Table 3. The method of belt fixation showed nine significantly high values among 12 persons (p50.01). Tables 4 and 5 show the intrarater reliability ICC (1,1) and ICC (1,3) and interrater reliability ICC (2,1) and ICC (2,3) for measurements with hand fixation and belt fixation. The ICC (1,3) and ICC (2,3) were 0.90 for both methods. There were no significant differences in the correlation coefficients of both measuring methods (all p50.05). Study 2 Measurement by the 20 examiners of the two subjects showed mean values of 152.0 ± 29.2 N in the male subject and 98.2 ± 9.0 N in the female subject (Table 6). When Examiners #15, #16, and #20 measured the muscular force of the male subject being tested, they felt hand movement even though a nonslip mat was used. Weight and BMI showed a high correlation coefficient (r ¼ 0.93), and multicollinearity was suspected, so weight was excluded as an independent variable for the analysis. Multiple regression analysis showed that the only variable affecting the measured values was dominant hand grip strength when testing the male subject (standardized partial regression coefficient ¼ 0.78, determination coefficient R2 ¼ 0.61, p50.01). For measurement in the female subject, no significant variables were found. The multiple regression equation obtained by analysis in the male subject was ‘‘61.4 + 2.1 (examiner’s dominant hand grip strength (kg)’’. In addition, the mean value of hip abductor muscle strength in the male subject as measured by the 20 examiners was assumed to be near the true value. Multiple regression analysis

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Table 4. Intrarater reliability of measurement of hip abductor muscle strength. Intrarater

ICC(1,1)

95%CI

ICC(1,3)

95%CI

SEM (N)

95%CI

MDC (N)

0.95 0.89 0.94

0.87–0.98 0.75–0.96 0.85–0.98

0.98 0.96 0.98

0.95–0.99 0.90–0.99 0.94–0.99

6.7 10.4 6.9

5.2–9.5 8.0–14.7 5.4–9.8

17.2 25.5 19.0

0.96 0.97 0.97

0.89–0.99 0.91–0.99 0.92–0.99

0.98 0.99 0.99

0.96–0.99 0.97–0.99 0.97–0.99

7.7 7.3 8.8

6.0–10.9 5.6–10.3 6.8–12.5

23.0 16.6 23.9

Hand fixation A B C Belt fixation A B C

ICC, Intraclass correlation coefficients; 95%CI, 95% confidence interval; SEM, Standard error of the mean; MDC, Minimal detectable change; A, Examiner A; B, Examiner B; C, Examiner C.

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Table 5. Interrater reliability of measurement of hip abductor muscle strength. Interrater

ICC(2,1)

95%CI

ICC(2,3)

95%CI

SEM (N)

95%CI

MDC (N)

0.78 0.79 0.76

0.27–0.94 0.31–0.94 0.22–0.93

0.92 0.92 0.90

0.53–0.98 0.58–0.98 0.45–0.98

10.1 10.3 9.3

7.8–14.3 7.9–14.5 7.2–13.1

26.5 19.9 20.0

0.93 0.90 0.93

0.83–0.98 0.77–0.97 0.83–0.98

0.98 0.96 0.98

0.94–0.99 0.91–0.99 0.93–0.99

11.1 13.9 11.1

8.6–15.8 10.8–19.7 8.5–16.1

27.8 30.9 28.0

Hand fixation First Second Third Belt fixation First Second Third

ICC, Intraclass correlation coefficients; 95%CI, 95% confidence interval; SEM, Standard error of the mean; MDC, Minimal detectable change; First, First try; Second, Second try; Third, Third try.

Table 6. Measurement of hip abductor muscle strength of study 2 (Units: N). Subject (1) Examiners 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

150 165 176 154 143 184 215 200 149 114 162 112 156 121 84 129 147 180 149 110

164 173 160 147 128 202 191 199 145 132 166 95 147 110 65 111 136 178 156 97

142 145 169 151 140 200 175 185 136 132 171 101 145 112 84 127 154 191 160 93

Mean

±

SD

152.0 161.0 168.3 150.7 137.0 195.3 193.7 194.7 143.3 126.0 166.3 102.7 149.3 114.3 77.7 122.3 145.7 183.0 155.0 100.0

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

11.1 14.4 8.0 3.5 7.9 9.9 20.1 8.4 6.7 10.4 4.5 8.6 5.9 5.9 11.0 9.9 9.1 7.0 5.6 8.9

Subject (2) 77 95 103 101 110 110 99 97 103 88 103 97 107 80 96 97 107 121 90 86

99 97 97 110 101 114 105 105 105 92 90 92 114 81 92 86 99 110 81 92

92 101 95 101 114 110 110 101 101 84 95 91 107 85 88 90 99 114 95 88

Mean

±

SD

p*

89.3 97.7 98.3 104.0 108.3 111.3 104.7 101.0 103.0 88.0 96.0 93.3 109.3 82.0 92.0 91.0 101.7 115.0 88.7 88.7

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

11.2 3.1 4.2 5.2 6.7 2.3 5.5 4.0 2.0 4.0 6.6 3.2 4.0 2.6 4.0 5.6 4.6 5.6 7.1 3.1

50.05 50.05 50.01 50.05 50.01 50.01 50.05 50.01 50.01 50.05 50.01 NS 50.05 50.05 NS 50.05 50.05 50.01 50.01 NS

*t-Test: Subject (1) versus Subject (2)

was similarly performed with the difference between the mean value and the actual value in the male subject as the dependent variable. The multiple regression equation obtained was ‘‘90.6 + 2.1 (examiner’s dominant hand grip strength (kg)’’.

Discussion Reliability when measuring hip abductor muscle strength using HHD In Study 1, intrarater reliability of the two methods was high, with an ICC (1,1)  0.89. The ICC (1,3) was higher (0.96), thus

showing even higher intrarater reliability when using the mean values of 3 measurements. These results are similar to previous reports (Kelln, McKeon, Gontkof, and Hertel, 2008; Rutherford and Hubley-Kozey, 2009; Traina et al, 2010; Vanpee et al, 2011; Widler et al, 2009). However, with hand fixation, the interrater reliability ICC (2,1) was 0.76–0.79 and the SEM was 9.27–10.25; with belt fixation, the ICC (2,1) was 0.90–0.93 and the SEM was 11.12–13.91. Since the SEMs were different, the results cannot simply be compared. Furthermore, there were no significant differences in the correlation coefficients of both measurement methods. However,

Hip abductor strength in HHD

DOI: 10.3109/09593985.2014.960539

examining the 95% CI of ICC, the belt fixation method showed high interrater reliability. This is because of differences in the stabilizing force between hand fixation and belt fixation. In addition, the ICC (2,3) was 0.90–0.92 with hand fixation, so that when using hand fixation, the mean value from at least 3 measurements must be used. Furthermore, the maximum MDC was 26.51 N with hand fixation and 30.90 N with belt fixation. From this result, when using both measuring method, changes beyond 30 N appear to be true changes.

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Increasing interrater reliability of the hand fixation method The results in Study 2 showed that measured values varied due to differences in upper extremity muscle strength of the examiners when hand fixation was used in subjects with strong hip abductor muscle strength. A strong hip abductor muscle has such high power that it moves the examiner’s hand. Based on these results, for testing in subjects with high hip abductor muscle strength, the measured values must be adjusted based on the upper extremity muscle strength of the examiner. For example, the multiple regression equation of ‘‘90.6 + 2.1  examiner’s dominant hand grip strength (kg)’’, which was obtained from the mean value of measurements in the male subject by 20 examiners and was assumed to be near the true value, can be used. If this multiple regression equation is used, then, for measurement of hip abductor muscle strength using hand fixation by an examiner with a grip strength of 50 kg, ‘‘90.6+2.1  50 [kg] ¼ 9.4 [N]’’. Therefore, the measurement value is the value obtained when 9.4 N is subtracted from the actual measured value. If the same calculation is performed for an examiner with a grip strength of 20 kg, 50.6 is added to the actual measured value. Thus, by arranging an examiner beforehand and assessing what degree of adjustment will be necessary based on the hip abductor muscle strength of the subject, the hand fixation method can be used even in persons with strong hip abductor muscle strength. However, in cases when weak muscle strength (the hand does not move) is anticipated during the period just after surgery, because no relationship with examiner grip strength was noted in a female subject with weak hip abductor muscle strength, there is little need for adjusting the hip abductor muscle strength values. This method is supported by the report which described the limit by hand fixation (Bohannon et al, 2012). Therefore, when conducting measurements in the early postoperative period, it is important to select the appropriate method. Based on the results to date, when measuring hip abductor muscle strength using a HHD in clinical practice, belt fixation, which has higher interrater reliability than hand fixation, is recommended. However, with belt fixation, because left and right hip abductor muscle strengths cannot be measured separately, contralateral lower extremity muscle strength may also affect measured values. Therefore, when measuring bilateral hip abductor muscle strength separately is important (i.e. in postoperative patients) verification using the hand fixation method is a good option. Future research As electromyographic analysis was not performed with the measurement methods in the present study, the actual degree of hip abductor muscle activity was unknown. In addition, with the hand fixation method, the cut-off values for determining to what extent a subject’s muscle strength was strong or weak was unclear. Therefore, future studies should also include electromyography to clarify to what extent measured values in subjects need to be adjusted.

151

Study limitations A limitation of this study was the use of healthy subjects, with no measurements in actual patients. However, previously reported methods included the use of special measuring equipment (Asayama et al, 2005; Cahalan, Johnson, Liu, and Chao, 1989; Downing et al, 2001; Jacobs et al, 2005; Kendall, Schmidt, and Ferber, 2010; Unlu et al, 2007) and the side-lying position (Widler et al, 2009), which require more time and are more physically burdensome to patients than the methods of the present study. With the present study methods, measurements can be easily performed in the supine position, which is especially useful for testing early postoperative patients. In addition, since the regression equation obtained in the present study was linear, care is necessary because its scope of application may be limited.

Conclusions Both measurement methods had high intrarater reliability. Moreover, in subjects with weak hip abductor muscle strength (the examiner’s hand was not moved), the physical characteristics of the examiners had no effect on measured values. Based on the present findings, in patients in whom weaker muscle strength is anticipated (i.e. soon after surgery) the methods used in the present study can be used to measure muscle strength. Belt fixation may be particularly useful to measure hip abductor muscle strength easily.

Declaration of interest The authors report no declarations of interest.

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Reliability of measurements of hip abduction strength obtained with a hand-held dynamometer.

This study aimed to evaluate intrarater and interrater reliability when measuring hip abductor strength in the supine position using a hand-held dynam...
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