Resaarch in Kinesiology
Federation of the Sports Pedagogues of the
Republic of Macedonia
Vol. 41, No. 2, pp. 150-153
VALIDITY OF THE TWO SYSTEMS FOR MEASURING
FORCE AND POWER OF THE LOWER EXTREMITIES
(Original scientific paper)
Ratko Stanković1, Katarina Herodek1, Branislav Dragić1, Saša Bubanj1 and Cvetko
Simonović2
1Unuversity of Niš, Faculty of Sport and Physical Education, Niš, Serbia
2High School for Educators, Gnjilane-Bujanovac, Serbia
Abstract
The main objective of this study was to investigate the correlation of mechanical properties of the
muscle force obtained from myotest (Copyright @ Myotest SA) and tensiometric platform (HBM @ German
& Serbian TRC), which are located at the Faculty of Sport and Physical Education in Nis. In this study, a
subject was performing a vertical jump by myotest protocol for a half squat jumping. During the jumps and
leaps each examinee carried myotest which was performed on tensiometric platform. Variables that were
treated in this study are: First maximum force measured in Newtons PF (N); Second time needed to obtain
power PT in milliseconds (ms); 3rd RFD force growth as an index of explosive strength. On the basis of the
research, the following conclusion could be done: The force, measured by the method set out in piezoelectric
devices tensiometric force sensors and platforms using electric accelerometers obtained within statistically
insignificant small difference. Thus, we have shown that these two types of measurements are very reliable.
Keywords: accelerographs transducer (Gymaware-GYM), accelerometer (Miotest-MIO),
platform to measure the force, the maximum measured force, the time for obtaining power,
the index of explosive strength, muscle force in the vertical jump, t-test, correlation coefficient
INTRODUCTION
An accelerometer is a device for measuring acceleration of the body in motion. It is used for various
purposes, the load indications, distance measuring, a
reference to the aircraft and missiles, and more. The
accelerometers work is based on measuring inertial
forces acting on the tool during movement. To the inertial mass, which is free to move in only one dimension
that direction acceleration acting, and she moves in line
with the current acceleration. Moving the weight is recorded and further used for the intended purpose. There
are accelerometers that do not use the principle of inertial mass movement except vibrations, change capacity,
optical abilities and others. Today you can buy a small
integrated accelerometers in the form of an integrated
circuit. Accelerometer for recording activity using devices is called accelerographs.
Platform system for measuring the force includes
a number of hardware units (electronic transformer
- platform itself, the signal for bringing the system in
certain conditions the device and recording device signals) and signal processing software. Each unit is in
this investigation. Together with the hardware platform
for bringing the system in certain conditions the device
RIK, (2), 2013
should lead to a good linearity, good range of measurement and others.
Available software could control the operation of
platforms for force and immediate processing, although
the user could make some choices. The main choices are
related to the measurement range of force and velocity
model. Force measurement range should be appropriate
for the activity, and if not excessively low (for example,
a small child) or too large (for example, when you take
a long or triple jump) default range is usually sufficient.
It is important to look for the recognizable sign is chosen so that the range of misfit, so wandering the center
of pressure coordinate values ​​of Ax and Az (range too
large) or smoothing the force Fy (range, too). Another
choice is a model of speed. A lot of this things has been
said about this in the past, but today AD converters and
computer storage capacity and processing speed are
high enough performance, so that’s not an issue. Model
at 500-2000 Hz can be seen in the current literature, but
the model at 1000 Hz offers the usual choice. It should
be noted, however, such overlapping spectrum (where
the higher the frequency of reflected and seen as a lower frequency in the data) occur due to the higher frequencies that may be seen in the signal. These higher
150
Stanković, Herodek, Dragić, Bubanj and Simonović
tem for measuring the strength and power were almost
not important, but a number of differences and improper
error ‘viewing angle, specially when lifting 20kg (PF
slope > 170 N, PF error > 335 N, PP slope > 400 W, PO
error > 878W). In summary, the assessment of PF and
PP and linear transducers mounted akcelometra showed
extremely strong correlation values, but these estimates
were limited by the presence of numerous errors and
slopes.
The main objective of this study was to investigate the correlation of mechanical properties of the muscle force obtained from myotest (Copyright @ Myotest
SA) and tensiometric platform (HBM @ German &
Serbian TRC), which are located at the Faculty of Sport
and Physical Education in Niš.
frequencies are usually removed before the electronic
filtering AD conversion, because it can not be removed
when the data are numerical. However, if the problem
is mounting platform (as noted above) the higher frequencies have very low amplitude and therefore is not a
problem for the user.
The purpose of this research (Comstock, et al.,
2011), was to determine the concordance values ​​Myotest
instrument for measuring the production of strength and
power exercises in weightlifting in the squat and bench,
with gold standard computerized linear transducers and
force measurement platforms. Fifty-four men (the bench:
39 - 171 kg, squat: 75-221 kg) and 43 females (bench,
18-80 kg, squat: 30-115 kg) (average age 18-30) did a
test of the strength of one repetition maximum (1MP) in
performing squats and bench. Testing procedures were
consisted of force from the jump squat exercise and
ejections at bench and in 30% of each subject’s 1MP.
During each measurement, the instrument Myotest and
Celesko linear transducer in direct cooperation with the
BMS system (Ballistic Measurement System, Entrance
panel technology for measuring force, Skye, South Australia) were placed on the pole for the weights. A strong
positive correlation between these two systems and the
determinants of high correlation (R2) was demonstrated
at the bench ejection force (r = 0.95, p, 0.05) (R2 = 0.92),
followed by casting bench strength (r = 0.96, p, 0.05)
(R2 = 0.93), the power of jump squat (r = 0.98, p, 0.05)
(R2 = 0.97), and the strength of the jump squat (r = 0.91,
p, 0.05) (R2 = 0.82). To conclude, when Myotest instrument set in the vertical axis of the barl, it is a valid instrument for measuring the force and power of the most
commonly used motions during the exercises.
The study (Crewther, 2011) investigated the validity of two kinematic systems for assessing the force
and power of the squat jumps. Twelve trained men did
series of exercises with weights of 20 kg, 40 kg, 60 kg,
80 kg, on Kistler portable measuring board. The usual
rectilinear transducer (Gymaware [GYM]) and accelerometer (Myotest [MIO]) were attached to the bar in
order to assess the highest accumulated force (PF) and
peak power (PP). Performed in all tests GYM and MYO
measurements were calculated to be PF and PP in a very
strong correlation (P ≤ 0.05-0.001) with the values ​​obtained from the plate to measure the force and strength (r
= 0.59-0.87 and r = 0.66-0.97). The differences between
the PF and PP values between
​​
2 and plate kinematic sys-
METHODS
In this study, a subject was performing a vertical
jump by myotest protocol for a half squat jumping. The
examinee took two protocols with hands on hips. The
total number of the presented was ten rebounds.
During the jumps and leaps each examinee carried myotest which was performed on tensiometric platform. Data acquisition was performed automatically by
myoest protocol, while data is collected manually from
the platform using a software package Catman (HBM
@ Germany).
Variables that were treated in this study are:
First maximum force measured in Newtons PF (N)
Second time needed to obtain power PT in milliseconds (ms) and 3rd RFD force growth as an index of
explosive strength.
All mechanical parameters will be obtained from
the curve force - time on the basis of standardized methods.
Statistical analysis, using the SPSS software, given
the inter correlation analysis and t-test examined differences paametara mechanical muscle force in the vertical
jump.
RESULTS
On the basis of programs and Catman Myotest
obtained values ​​of maximum force PF time to achieve
that power PT. RFD values were
​​
calculated from the ratio of PF / PT.
Descriptive statistics
Table 1. Descriptive Statistics
Variables
PF
PT
RFD
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Device
N
Mean
Std. Dev.
PL
MY
PL
MY
PL
MY
10
10
10
10
10
10
1705.17
1654.20
269.90
295.00
6.44
5.15
86.03
119.87
37.79
.00
1.05
.81
151
Std.
Error
27.20
37.91
11.95
.00
.33
.26
Stanković, Herodek, Dragić, Bubanj and Simonović
Table 2. Correlation matrix betweeн the variables
Variables
PF
PT
RFD
PF
PT
RFD
1.00
- .322
.655 **
- .322
1.00
- .811 **
.655 **
- .811 **
1.00
Table 3. Values ​​of T-test
Variables
PF
PT
FD
F
Sig.
.863
8,38
159
.365
.010
.695
t
df
Sig.
Mean
Dif.
Std.Error
Dif.
1,092
2,100
,087
18
18
8
.289
.050
.006
50.10
-25.10
1.29
46.66
11.95
.4189
Table 1 shows the values of
​​ the measures of central tendency and measures of dispersion. Also, in the
last column to the data error of the mean. These measures of descriptive statistics shows that there are differences between them when it comes to data obtained with
different measuring instruments. However, the mean
differences above all, do not point out that if there is
a statistically significant difference, as will be seen in
subsequent analyzes.
platforms using electric accelerometers obtained within statistically insignificant small difference. Thus, we
have shown that these two types of measurements are
very reliable.
Second: The time required to develop maximum
force was different. Most likely the reason for the great
difference in the number of sampling and frequency of
the devices. The myotest operates at a frequency of 200
Hz while the platform surface tension, and its sensors
were set to 2000 Hz. This difference of as much as 10x is
probably the cause of the obtaining of various arithmetic
mean value of the maximum time measurement.
Correlation between variables
From Table 2, we see a high correlation index of
explosive strength RFD with variable maximum force
and maximum PF PT time that the significance level of
0.01. T is somehow expected, given that the index is calculated as the ratio of these two measures.
Correlation between the maximum force and PF
time to achieve that force PT is not statistically significant (- .322), and its negative sign indicates an inverse
proportionality.
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Analysis of arithmetic means
Table 3 shows the values ​​studnetovog t-test for
independent samples was small. Statistical significance
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has reached the maximum force which can be the reason
of different sampling, ie, different frequencies of operation. As a consequence of the previous significant difference was observed in the index of explosive strength,
which was expected.
CONCLUSION
On the basis of the research in order to identify
differences in the measurement of the mechanical properties of vertical jump, the following conclusion could
be done:
First: The force, measured by the method set out
in piezoelectric devices tensiometric force sensors and
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152
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Correspondece:
Ratko Stanković
Unuversity of Niš
Faculty of Sport and Physical Education
Čarnojevića 10a, 18000 Niš, Serbia
E-mail: [email protected]
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