Reliability of Isometric Knee Extension Muscle Strength Measurements of Healthy Elderly Subjects Made with a Hand-held Dynamometer and a Belt

Abstract

[Purpose] The purpose of this study was to examine the reliability of three isometric knee extension strength measurements (IKE) made with a hand-held dynamometer (HHD) and a belt of healthy elderly living in the community as subjects. [Subjects] The subject cohort consisted of 186 healthy elderly people, aged 65 to 79 years, living in local communities. [Methods] IKE of the leg subjects used to kick a ball was measured. IKE of each subject was measured three times using an HHD-belt at intervals of 30 seconds. The reliability of the larger of the first two measurements (LV2) as well as the third measurement (3V) was investigated. [Results] The intraclass correlation coefficients [ICC (1, 1)] for LV2 and 3V were 0.955. Bland-Altman analysis showed a fixed bias, and the limits of agreement ranged from -5.6 to 4.6. [Conclusion] The ICC results show that the test-retest reproducibility of IKE measurements of healthy elderly subjects using an HHD-belt is high. However, Bland-Altman analysis showed a fixed bias, suggesting the need for three measurements.

Full text

Reliability of Isometric Knee Extension Muscle
Strength Measurements of Healthy Elderly Subjects
Made with a Hand-held Dynamometer and a Belt
Munenori Katoh, PT, PhD
1)*
, Koji isozaKi, PT, PhD
2)
1)
Department of Physical Therapy, Faculty of Health Science, Ryotokuji University: 5-8-1 Akemi,
Urayasu-City, Chiba 279-8567, Japan
2)
Department of Shizuoka Physical Therapy, Faculty of Health Science, Tokoha University, Japan
Abstract. [Purpose] The purpose of this study was to examine the reliability of three isometric knee extension
strength measurements (IKE) made with a hand-held dynamometer (HHD) and a belt of healthy elderly living in the
community as subjects. [Subjects] The subject cohort consisted of 186 healthy elderly people, aged 65 to 79 years,
living in local communities. [Methods] IKE of the leg subjects used to kick a ball was measured. IKE of each sub-
ject was measured three times using an HHD-belt at intervals of 30 seconds. The reliability of the larger of the rst
two measurements (LV2) as well as the third measurement (3V) was investigated. [Results] The intraclass correla-
tion coefcients [ICC (1, 1)] for LV2 and 3V were 0.955. Bland-Altman analysis showed a xed bias, and the limits
of agreement ranged from −5.6 to 4.6. [Conclusion] The ICC results show that the test-retest reproducibility of IKE
measurements of healthy elderly subjects using an HHD-belt is high. However, Bland-Altman analysis showed a
xed bias, suggesting the need for three measurements.
Key words: Hand-held dynamometer, Healthy elderly subjects, Knee extension muscle strength
(This article was submitted Apr. 11, 2014, and was accepted May 22, 2014)
INTRODUCTION
Various physical functions deteriorate with age, and the
word sarcopenia is clinically used to describe this age-relat-
ed decrease in muscle mass
1)
. Based on previous studies
2–6)
,
the consensus statement of the European Working Group on
Sarcopenia in Older People (EWGSOP) notes that a diag-
nosis of sarcopenia requires reductions in muscle mass and
muscle function (muscle strength and physical capabilities).
The muscle strength of the lower limbs can be assessed by
evaluating standing up from a chair
7, 8)
, gait
9–15)
, going up
and down stairs
8)
, and by falls
16, 17)
. Most intervention stud-
ies aimed at preventing elderly people from falling include
training to strengthen the muscles of the lower limbs
18–38)
.
The muscle strength of the lower limbs can be assessed
quantitatively by measuring the isometric knee extension
strength with the knee joints exed at 90 degrees. A hand-
held dynamometer (HHD) is a tool that is relatively easy to
operate and is frequently used to quantify muscle strength.
However, holding an HHD in the hand may limit subjects’
performance in the task being tested. The upper limit of
measurement using an HHD was found to be 30 kg, regard-
less of measurement experience and ability to apply resis-
tance
39)
. Fixation was reported to be difcult to achieve at
or above 300 N
40)
, and at 85 N/m or higher
41)
. An investiga-
tion of 36 Japanese subjects found that the average maxi-
mum weight loads that male and female testers were able to
measure 27.6 kg and 19.0 kg, respectively, much lower than
those reported previously
42)
.
The primary disadvantage of measurements with HHD
alone is that the investigators do not usually have the up-
per limb strength to fully restrain the subjects. To overcome
this disadvantage, a method using a belt with an HHD was
developed to measure the muscle strength of the lower
limbs
43–45)
. The reproducibility and adequacy of the HHD
alone and with a belt (HHD-belt) in measuring muscle
strength has been compared in healthy males and females
aged approximately 20 years
43–45)
. The reproducibility of
measurements of knee extension muscle strength has been
investigated among investigators, between measurement
methods, and between test-retests
43)
. The intraclass cor-
relation coefcients (ICC) between investigators [ICC (2,
1)] were 0.04 without a belt and 0.98 with a HHD-belt, and
Pearson’s product moment correlation coefcient between
the measurement methods was 0.61 for male investigators
and 0.31 for female investigators. The ICCs (1, 1) between
test-retest were 0.94, 0.96 and 0.96 for three trials and 0.89
among the three trials
44)
. A comparison of the HHD-belt
method with an isokinetic muscle strength measurement
device yielded a Pearson’s product moment correlation co-
efcient for isometric knee extension muscle strength of
0.75
45)
.
The test-retest reproducibility of measurements of iso-
J. Phys. Ther. Sci.
26: 1855–1859, 2014
*Corresponding author. Munenori Katoh (E-mail: mu-kato@
ryotokuji-u.ac.jp)
©2014 The Society of Physical Therapy Science. Published by IPEC Inc.
This is an open-access article distributed under the terms of the Cre-
ative Commons Attribution Non-Commercial No Derivatives (by-nc-
nd) License <http://creativecommons.org/licenses/by-nc-nd/3.0/>.
Original Article

J. Phys. Ther. Sci. Vol. 26, No. 12, 20141856
metric knee extension muscle strength has also been es-
timated for hemiplegic patients, for patients who had re-
ceived surgery for femoral head fractures, and for healthy
elderly people
46–48)
. The ICCs (1, 1) for hemiplegic patients,
obtained from 3 measurements performed on the same day
were 0.98 for session 1 and 0.99 for session 2 on both the
paralyzed and non-paralyzed sides
46)
. For patients who had
received surgery for femoral head fractures, the ICCs (1,
1) on the same day were 0.948 for the fractured leg, 0.953
for the non-fractured leg and 0.961 for the average of both
legs
47)
. The ICCs (1, 1) for healthy elderly males and fe-
males, from two measurements on the same day were 0.91
and 0.88, respectively
48)
. An increase of 10% was observed
in the second measurement for approximately 50% of the
healthy elderly subjects, suggesting the necessity of basing
ICCs on three consecutive measurements
48)
.
If the third measurement of healthy elderly subjects were
higher than the second, then the third measurement may
be more appropriate. However, performing three measure-
ments requires more time and a larger number of investi-
gators. Therefore, comparing the second and third of three
consecutive measurements of healthy elderly subjects may
elicit information about the adequacy and practicality of
these measurements.
The purpose of this study was to examine the reliabil-
ity of three consecutive isometric knee extension strength
measurements (IKE) made with a hand-held dynamometer
and a belt of healthy elderly subjects living in the commu-
nity.
SUBJECTS AND METHODS
The study cohort comprised 186 of 235 healthy elder-
ly people living in local communities who participated
in physical strength test programs in 2010 and 2011 or-
ganized by the government of a city with a population of
about 250,000 people. Subjects were excluded if they <65
or >79 years old, if they had participated in a similar pro-
gram in 2009 or earlier, if they had knee joint pain, or if
they had any other diseases or pain conditions that would
have affected measurements of muscle strength. If a subject
had participated in the program in both 2010 and 2011, the
values obtained in 2010 were analyzed. The 186 subjects
comprised of 66 males with an average height of 163.6 cm
(SD = 6.0 cm) and an average body weight of 61.4 kg (SD =
6.7 kg), and 120 females with an average height of 150.9 cm
(SD = 4.8 cm) and an average body weight of 52.3 kg (SD
= 6.4 kg). The subjects were divided into three age groups,
65 to 69, 70 to 74, and 75 to 79 years, as shown in Table 1.
Approval was obtained from the research ethics committee
of Ryotokuji University and from the city administration,
which had organized the physical strength test program, to
use the data for this study. All subjects provided their writ-
ten informed consent.
Isometric knee extension muscle strength was measured
using a µTas F-1 hand-held dynamometer (Anima Corp.,
Tokyo, Japan). Subjects sat on a training bench and adjusted
the position of their gluteal regions so that leg of bench was
posterior to the lower limb being measured. The leg mea-
sured was that used to kick a ball. The height of the training
bench was set so that each subject’s legs were slightly above
the oor. Subjects maintained their trunk in a perpendicu-
lar position with both hands touching the bench surface on
either side of the trunk. A large folded towel was placed
under the popliteal fossa of each subject, with one femur
maintained horizontally with the knee joint set at an angle
of 90 degrees, and both lower legs hung perpendicular to
the oor.
The HHD sensors was placed on the distal anterior sur-
face of the lower leg, and the lower edge of the HHD was
xed with a hook-and-loop fastener at the height of the up-
per edge of the malleolus medialis. A belt was placed over
the HHD and tied to the leg of a bed. Maximum effort in
knee joint extension movement was exerted for about ve
seconds and repeated twice more at intervals of ≥30 sec-
onds between exertions. The examiner was a man, of height
180 cm and weight 54 kg, highly familiar with this method
of measuring, but he was not informed of the results. In ad-
dition, the research assistant who recorded the results was
blinded to the purpose of the research.
The larger of the rst two measurements (LV2) was uti-
lized. The difference between the third measurement (3V)
and LV2 [∆3V=3V-LV2] and the ratio of ∆3V to body weight
(∆3V/BW) were calculated. The results of all the study sub-
jects and of the three age groups were analyzed.
The necessity of performing the third measurement was
assessed by determining ICC (1, 1) for LV2 and 3V as well
as by Bland-Altman analysis. SPSS ver.15.0 J for Windows
and R2.8.1 were used for statistical analyses; p-values <0.05
were considered statistically signicant.
RESULTS
The average values for all subjects were 31.9 kgf for LV2,
32.4 kgf for 3V, 0.5 kgf for ∆3V, and 0.010 kgf/kg for ∆3V/
BW (Table 2). Increases in ∆3V and in ∆3V/BW, as well as
the numbers of proportion of subjects showing increases in
each group, are shown in Tables 3 and 4. For 54.8% of all
subjects, the 3V measurements were higher than LV2. In
addition, 11.3% of the study subjects showed ∆3V increases
of ≥5 kgf, and 2.7% showed increases of ≥10 kgf (Table 3).
Moreover, ∆3V/BW increased by ≥0.05 kgf/kg (5% of body
weight) in 16.7% of these subjects and by ≥0.100 kgf/kg
Table 1. Subject group proles
Gender
Age group
(yrs)
n Height (cm) Weight (kg)
Female 120 150.9 (4.8) 52.3 (6.4)
65 to 69 75 151.1 (4.3) 51.9 (6.2)
70 to 74 37 150.8 (5.2) 53.2 (7.4)
75 to 79 8 149.9 (7.2) 52.5 (2.8)
Male 66 163.6 (6.0) 61.4 (6.7)
65 to 69 29 164.5 (5.8) 60.9 (5.8)
70 to 74 29 163.4 (6.7) 61.5 (8.7)
75 to 79 8 161.0 (3.4) 63.2 (4.9)
Mean (SD)

1857
(10% of body weight) in 5.4% (Table 4).
The results of ICC and Bland-Altman analysis of LV2
and 3V are shown in Table 5. ICC (1, 1) of all subjects was
0.955 and was 0.9 or higher for all three age groups (Table
5). Bland-Altman analysis showed a xed bias, with limits
of agreement for all subjects between −5.6 and 4.6 (Table 5
and Fig. 1).
DISCUSSION
Physical strength measurement programs for healthy
elderly people are run by the city administration, both to
prevent elderly people from requiring nursing care and to
improve their health. Individuals are invited to participate
in these programs at places such as community centers.
These programs are designed to assess as many individuals
as possible in a short period of time, making it necessary to
minimize the time spent assessing each participant.
Table 2. Isometric knee extension muscle strength values of elderly people, as measured by a hand-held
dynamometer with a belt
Age group (yrs) n LV2
a)
3Vb
b)
∆3V
c)
∆3V/BW
d)
kgf kgf kgf kgf/kg
All subjects 186 31.9 (10.1) 32.4 (10.1) 0.5 (3.0) 0.010 (0.054)
65 to 69 104 31.2 ( 9.9) 32.0 (10.1) 0.5 (3.4) 0.015 (0.049)
70 to 74 66 39.8 ( 9.8) 40.2 ( 8.9) 0.4 (2.7) 0.011 (0.059)
75 to 79 16 29.7 (10.2) 31.0 (10.3) −1.3 (3.5) −0.023 (0.064)
Mean (SD),
a)
The largest value of the rst two measurements,
b)
The value of the third measurement,
c)
3V-LV2 ,
d)
∆3V/body weight
Table 3. Increase from the largest value out of the rst two measurements to the value of the third measurement (∆3V*)
Age group (yrs) n 0 kgf< 5 kgf≤ 10 kgf≤ 15 kgf≤ 20 kgf≤
All subjects 186 102 (54.8) 21 (11.3) 5 (2.7) 1 (0.5) 0
65 to 69 104 63 (60.6) 14 (13.5) 5 (4.8) 1 (1.0) 0
70 to 74 66 33 (50.0) 7 (10.6) 0
75 to 79 16 6 (37.5) 0
No. of subjects (proportions shown in percent), *The value obtained in the third measurement − The largest value out of
the rst two obtained measurements
Table 4. Increase from the largest value out of the rst two obtained measurements to the value of the third measurement,
divided by bodyweight (∆3V/BW
#
)
Age group (yrs) n 0.000< 0.050≤ 0.100≤ 0.150≤ 0.200≤
All subjects 186 102 (54.8) 31 (16.7) 10 (5.4) 2 (1.1) 0
65 to 69 104 63 (60.6) 18 (17.3) 5 (4.8) 1 (1.0) 0
70 to 74 66 33 (50.0) 13 (19.7) 5 (7.6) 1 (1.5) 0
75 to 79 16 6 (37.5) 0
No. of subjects (proportions shown in percent), #(The value obtained in the third measurement − The largest value out of
the rst two obtained measurements) / Body
Table 5. Reliability of the largest value out of the rst two measurements, and the value in the third measurement
ICC (1,1) Bland-Altman analysis
Age group (yrs) n
point
estimation
95% CI LOA
xed bias proportional bias
95% CI bias* slope** bias*
All subjects 186 0.955 (0.940–0.966) −5.6–4.6 −0.4–−0.6 exist 0.004 p=0.83 n-ex
65 to 69 104 0.955 (0.940–0.966) −5.4 –3.7 −0.7–−1.0 exist −0.210 p=0.45 n-ex
70 to 74 66 0.957 (0.938–0.970) −5.0–4.1 −0.2–−0.6 exist 0.022 p=0.56 n-ex
75 to 79 16 0.937 (0.834–0.977) −2.5–5.1 −0.1–−0.5 exist 0.008 p=0.93 n-ex
ICC: intraclass correlation coefcient, 95% CI: 95% coefcient interval, LOA: limits of agreement, *: presence of bias, exist:
present, n-ex: not-present, **: Slope of regression line

J. Phys. Ther. Sci. Vol. 26, No. 12, 20141858
An investigation of the reproducibility of two sets of
measurements of 183 healthy elderly subjects who partici-
pated in a physical strength measurement program run by
a city administration found that the ICC (1, 1) for the two
measurements was 0.91 for males and 0.88 for females
47)
.
However, 46% of males and 49% of females showed in-
creases of ≥10% in the second measurement, and 17% and
23%, respectively, showed increases of ≥20%. These results
led to our use of the higher of the values obtained in the two
sets of measurements, and indicated the necessity of per-
forming three consecutive sets of measurements.
The results presented here indicate that high reproduc-
ibility can be obtained when three measurements are per-
formed, because the ICCs for LV2 and 3V were ≥0.9 for
both males and females. However, the highest values for
at least 50% of the study participants were obtained in the
3V measurement. Moreover, a comparison of LV2 and 3V
found that 16.7% of subjects showed an increase of ≥0.050
kgf/kg in 3V. Therefore, limiting the number of measure-
ments to two may yield lower than actual muscle strengths
for more than half the subjects, and lead to the bodyweight
ratio being recorded at least 0.050 kgf/kg lower, equivalent
to 5% of bodyweight, for 1 in 6 subjects. A lower than ac-
tual bodyweight ratio in knee extension muscle strength can
affect the interpretation of relationships between muscle
strength and motions such as gait. These ndings suggest
that performing three measurement trials is appropriate for
gaining more accurate measurements of IKE of healthy el-
derly people.
Bland-Altman analysis found a xed bias with negative
values, with LV2 lower than 3V, and a range of +5.6 kgf and
−4.6 kgf for two measurements.
An investigation of Mini-Mental State Examination
Scores of different age groups, intervals of 5 years, found
that the scores decreased with age
49)
. Since the IKE of our
study subjects may also decrease with age, subjects were
divided into three age groups, 65 to 69, 70 to 74, and 75
to 79 years. None of the subjects in the 75 to 79-year-old
group showed increases in ∆3V of ≥5.0 kgf or in ∆3V/BW
of ≥0.050 kgf/kg. We hypothesize that increases in the third
measurement are smaller in this age group than in the other
age groups, suggesting that the third measurement may not
be required for subjects aged 75 to 79 years.
Further increases in the number of measurements should
be considered for subjects aged 65 to 74 years, since a
higher proportion of subjects in this group than in the other
group showed the highest measured value in the third mea-
surement. However, time constraints may preclude four or
more measurements per subject.
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