A Novel Inertial Technique to Measure Very High Linear and Rotational Movements in Sports, Part I: The Hardware
In sports biomechanics, videography provided an indirect
measurement method for measuring sport movements. However, these techniques
are expensive, bulky and not portable. A novel inertial data logger designed
to record the linear and rotational movements in three axes at 200 Hz
and save the data on a memory card. A custom PC software was developed
to measure the kinematics parameters (linear and angular accelerations
and velocities) and compute the kinetic parameters (force, torque, angular
momentum, impulse and angular power) of the attached limb during performance.
The current system is applicable in sports that involve high linear and
rotational kinematics and high impact contact. Evaluation of the sensor
module at 500 °/sec showed very good validity and reliability of angular
velocity (r = 0.954, p<0.0001; Cronbachs Alpha = 0.973) and angular
acceleration (r = 0.905, p<0.0001; Cronbachs Alpha = 0.960),
respectively as compared to values obtained at 300 and 210 °/sec.
It is able to measure angular velocity up to ± 100,000 °/sec
and linear acceleration up to 2,452 m/sec2. This is light,
cheap, reliable, robust and accurate system to measure high kinematic
and kinetic parameters in the field. This approach is in contrast to current
high-tech videography systems that are expensive, bulky and cumbersome.
This novel technique is suitable in Soccer, Rugby, American Football,
Tennis, etc. to evaluate the players performance in the field.
Biomechanical techniques providing knowledge of essential mechanisms for enhancing
performance and learning of sports skills (Lees and Nolan,
1998). In this regard, optical motion analysis systems such as videography,
photography, cinematography and opto-electric techniques provided indirect measurement
methods for the motion analysis. These systems are however expensive, bulky
and not portable. Their installation and calibration is time consuming and needs
professional staff. In addition, their output data need digitization and smoothing
before process and analysis. When using videography methods, application of
some filtering techniques may significantly alter the displacement signal by
cutting the high frequency components leading to an underestimation of the true
displacement, velocity and acceleration patterns in the moment of impact (Kellis
and Katis, 2007). Most of these systems require a restricted and controlled
With the advent of inertial sensing technology and miniaturization in sensor
technology coupled with the production of powerful microcontrollers, miniature
sensors, high capacity memories and small batteries, the possibility for designing
portable recording systems usable either in the field or for long-time ambulatory
measurements became a reality. Consequently, these recording systems were used
to monitor and measure a variety of physical activities involving low range
motion analysis (Aminian et al., 2001, 2002;
Meamarbashi and Burhanuddin, 2006; Salarian
et al., 2004; Willemsen et al., 1990)
and in swimming (Ohgi et al., 2002; Ohgi
and Yasumura, 2000).
Accelerometers and gyroscopes operate on the principle of inertia. Accelerometers
are sensors that measure the applied linear acceleration produced by the movement
acting along their sensitive axis (Mathie et al.,
2004). Gyroscopes (angular rate sensors) alone or in combination with accelerometers,
electromagnetic sensors and digital compasses were employed for low range motion
analysis as evidenced by earlier published reports on monitoring physical activities
(Bussmann et al., 2000; Inoue
et al., 2003; McMillan et al., 2005),
gait analysis (Kavanagh et al., 2006; Scapellato
et al., 2005; Willemsen et al., 1990),
clinical investigations related to fall risk in the elderly (Cho
and Kamen, 1998; Najafi et al., 2002), orthopaedic
outcome (Jaecques et al., 2003) and some sport
performances (Davey et al., 2005; Ohgi
et al., 2002). However, this combination is not able to measure high
angular kinematics in most of sports especially in the field.
It is necessary to mention if highest range ( ± 1200 °/sec) triaxial
angular rate sensor (gyroscope) available in the market (MEMSENSE,
2007; Xsens, 2007) incorporated with triaxial accelerometer
(> ± 100 gravity) still this configuration could not be able to measure
high angular velocity of high sport movements (>2000 °/sec) due to low
measurement range and its low bandwidth of gyroscopes. It therefore becomes
necessary to design a sensor module with a configuration that can measure directly
the high linear and rotational kinematics as an alternative to videography.
In the realm of mechanics an inertial system without using gyroscope is called
Gyroscope-Free system. A gyroscope-free inertial system is a system that only
uses accelerometer measurements to compute the linear displacement and angular
rotation of a moving rigid body. To achieve this, the accelerometers need to
be strategically distributed on the rigid body (Tan and Park,
The complete state of acceleration of a rigid body is specified by its
linear acceleration and angular velocity. The acceleration of any point
(P) of the body is:
ap= aO + ώ x (P
O) + ω x (ω x (P O))
where, aO is the acceleration of a point O on the body and
ω and ώ are the body angular velocity and acceleration and P
O is the relative position of P with respect to O.
In the rigid body, angular acceleration and centripetal acceleration
are always perpendicular and total acceleration vector of any point calculating
by Eq. 1.
In theory, a Gyroscope-Free configuration using only accelerometers provides
this possibility. Theoretically, a minimum of six accelerometers are required
for a complete description of a rigid body motion in a cube shaped configuration
(Tan and Park, 2002; Nevalainen, 2008;
Park et al., 2005). However, the number of accelerometers
needed for the measurement of any particular kinematic parameter is determined
by the configuration of the accelerometers, location, orientation and the computational
method for the accelerometer output. It would seem therefore that accelerometers
could be used in many sports for the measurement of high linear and rotational
kinematics and also in high impact sports.
In this method, traditional analytical methods are replaced with an innovative
method to process two triaxial accelerometers and one axis (Z) accelerometer
parallel to the rigid body. Different with previous methods that used
cube-shape configuration with six uniaxial accelerometers and placement
of accelerometers are strategic, this method mounted accelerometers in
planar board only. Planar configuration giving highest accuracy in electronic
placement of accelerometers and significant reduce the orientation errors.
Earlier researchers applied mathematical procedures to solve the accelerometers
output by solving the matrix but in this method exploited some geometrical
procedures. In this design tried to miniaturize the electronic parts,
reduce the product cost to be more applicable in movement analysis applications
in the filed of medicine and sports biomechanics where the current systems
are cumbersome and not appropriate for measurements out of laboratory.
Consequently, the present project was undertaken to design and manufacturing
a sensor module and a data logger integrated with professional software
using only accelerometers in a special configuration and orientation that
is capable of directly measuring the high linear, angular acceleration
and angular velocity in three axes. This system was then applied to compare
the left and right legs kinematics and kinetics of instep kick in soccer.
MATERIALS AND METHODS
Equipment and software: Accelerometers (Freescale Semiconductor,
Arizona, USA) were used in the design of the current data logger and sensor
module. In the data logger, a built-in triaxial accelerometer consisting
of a dual-axis (X-Y) and mono-axial (Z) accelerometers were implemented.
In the sensor module, two dual-axis (X-Y) and three mono-axis (Z) accelerometers
were used (Fig. 2). A block diagram and schematic diagram
of the data logger and sensor module shown in Fig. 1.
The sensor module (weight = 80 g, dimensions = 23x2.3x4 cm) and data
logger system (weight= 70 g, dimensions = 6x5.7x2.5 cm) shown in Fig.
2 designed based on the differentiation of parallel axes acceleration
and geometric configuration of the accelerometers using the principle
of rigid body dynamics. This sensor module is capable of measuring high
rotational acceleration in three axes as well as magnitude of two-dimensional
angular velocity (X-Z) without using a gyroscope in the following way.
Two dual axis (X-Y) and two mono-axial (Z) accelerometers were mounted
on a Printed Circuit Board (PCB), 20 cm apart with similar axis parallel
to each other. This arrangement allowed for the measuring of rotational
and linear acceleration that is independent of the axis of rotation and
eliminates the effect of gravity on the computation of rotational kinematics.
The analog output of parallel axes (e.g., X1 and X2,
etc.) simultaneously sampled by two fast 16-Bit A/D converters.
|| A block diagram showing the sensor module and data
|| Configuration of the sensor module
In order to measure the shank rotation (internal/external rotation) during
an instep kick, a third Z-axis accelerometer (Z3) was mounted
on a small PCB inside the aluminium case. This PCB was placed parallel
and co-central with the main PCB sensor module board 3.5 cm apart. The
analog output of each accelerometer axis simultaneously digitised by 16-bit
A/Ds. The sensor module was enclosed in an aluminium case and connected
to the data logger by external cable. The data logger had an ultra-high
speed microcontroller, a 32 MB Multimedia Card (MMC), a built-in triaxial
accelerometer ( ± 40 gravity) and a 16-bit A/D converter. The accelerometers
output (10 axes) were saved on memory card at 200 Hz.
Measurement of kinematics parameters and calculation of kinetic parameters:
The linear acceleration values from each set of triaxial accelerometer
and the parallel Z-axis accelerometer are recorded and linear and rotational
kinematic and kinetic parameters derived with the designed software. In
this way, the effect of gravity and linear acceleration of each parallel
axes would be the same.
Another feature of this design is that even though the rotational kinematics
is dependent on the distance between the two parallel accelerometers yet
it is insensitive to the axis of rotation.
A comparative study of kinematic measurement of the sensor module:
The validity and reliability of the angular velocity and angular acceleration
of sensor module had verified in controlled condition. It had been tested
by comparing with Biodex isokinetic machine (Model 2.15). Biodex afforded
a chance to compare angular velocity and angular acceleration in controlled
conditions. The sensor module was fixed to the lever arm of the Biodex.
Five male healthy volunteers with ages ranging from 25-35 years were selected
for this part of the study. The information form and methodology had previously
approved by the university ethical committee. Subjects were requested
to exercise on a cycle ergometer at 25-50 W for 3-5 min and then followed
by leg stretches for 2-3 min.
Subjects were asked to sit on the Biodex chair after which the attachments
of the dynamometer were readjusted accordingly. The knee was positioned 5 cm
away from the lever arm axis. A calf pad was placed 5 cm proximal to the lateral
malleolus and secured with a padded shin strap. Subjects were stabilized with
thigh and shoulder straps (Taylor et al., 1991).
The range of motion of the lever was adjusted between 0-90°. The subjects
were made to perform three series of five repetitions of extension and flexion
of the knee at three angular velocities: 500, 300 and 210 °/sec. Three minute
rest was given between each test to minimize muscle fatigue.
Statistical analysis: After processing the raw data, the results
transferred into an SPSS format for statistical analysis. The level of
significance was set at p<0.05. Results are reported as Mean ±
SD. SPSS software (SPSS, Chicago, Illinois) was used for the statistical
analyses (version 12.0).
Simple regression was used for the validity test and Cronbachs
coefficient alpha was used as a measure of internal consistency for the
reliability test of the kinematic parameters.
Comparison of the measured angular velocity between biodex and sensor
module accelerometers: Comparison of the recorded magnitude of angular
velocity measured by the sensor module accelerometers (Gyroscope-Free
system) and Biodex for five subjects at 500, 300 and 210 °/sec is
shown in Table 1. The angular velocity values of the
Biodex as compared to that of data logger sensor module were statistically
analysed. Using a simple regression and reliability test (Cronbachs
Alpha), a very good relationship and reliability between the Biodex and
the data logger angular velocity values of the lever arm movement at 500
and 300 °/sec were found. The r, R2 and Cronbachs
Alpha were lower at 210 °/sec when compared to that at 500 °/sec.
An example of tracings of the magnitude of angular velocity during five
extension/flexion of a subjects shank recorded by the Biodex and
data logger at a preset level of 500 °/sec is shown in Fig.
Comparison of the angular acceleration measured by the biodex and
sensor module accelerometers: Computed angular acceleration (rad/sec2)
values of the Biodex compared to that of the data logger sensor module
for five subjects were statistically analysed. Using a simple regression
and Cronbachs Alpha, there was a very good relationship and reliability
between the Biodex and the data logger angular acceleration values of
the lever arm movement at 500, 300 and 210 °/sec (Table
2). The r, R2 and Cronbachs Alpha were higher at
500 °/sec compared to 210 °/sec.
A sample recording of the angular acceleration at 500 °/sec obtained
from the Biodex and data logger sensor module during five extension/flexion
of the shank is shown in Fig. 4.
|| Comparison of the angular velocity at 500, 300 and
210 °/sec between Biodex and data logger sensor module accelerometers
|*95% confidence Interval of the b
A graphical comparison between the magnitude of angular
velocity at 500 °/sec measured by the Biodex and accelerometers
of the sensor module during five extension/flexion of a subject shank
||Tracings of angular acceleration (rad/sec2)
obtained with the Biodex and data logger sensor module during five
extension/flexion of the shank at 500 °/sec
|| Comparison of the angular acceleration at 500, 300
and 210 °/sec of biodex and data logger sensor module accelerometers
|*95% confidence Interval of the b
The study of multiple segments is the great advantage of vidography. However,
these techniques are considering indirect measurement methods. In this research,
a novel direct measurement method applied to measure the sport performance in
the field. It is light, small, portable, cheap, fast, robust, flexible and adaptable
to many sports. It can measure angular velocity up to ± 100,000 °/sec
and linear acceleration up to 2,452 m/sec2 in Z and 981 m/sec2
in X and Y axes. However, for the multi-segment study, the instrument can be
attached to each segment and use in a sensor network. This novel technique is
also suitable in many of other sports or in the low range movements (e.g., gait,
dance, etc.) using low range accelerometers. Using lower accelerometer range
for low range motion analysis will increase the precision of the system. This
method is valuable to improve the skill and identify the neuromuscular problems
through training and retests. This method provided a rapid evaluation in the
field for the coaches to understand the players skill level and correct
Special thanks go to all the students who have participated in this study
for their enthusiasm, full co-operation during the laboratory and field
1: Aminian, K., B. Najafi, C. Bula, P.F. Leyvraz and P. Robert, 2001. Ambulatory gait analysis using gyroscopes. Proceedings of the 25th Annual Meeting of the American Society of Biomechanics, August 7-11, 2001, American Society of Biomechanics, San Diego, USA., pp: 309-310.
2: Aminian, K., B. Najafia, C. Bülab, P.F. Leyvrazc and P. Robert, 2002. Spatio-temporal parameters of gait measured by an ambulatory system using miniature gyroscopes. J. Biomech., 35: 689-699.
CrossRef | Direct Link |
3: Bussmann, J.B., I. Hartgerink, L.H. van der Woude and H.J. Stam, 2000. Measuring physical strain during ambulation with accelerometry. Med. Sci. Sports Exercise, 32: 1462-1471.
Direct Link |
4: Cho, C.Y. and G. Kamen, 1998. Detecting balance deficits in frequent fallers using clinical and quantitative evaluation tools. J. Am. Geriat. Soc., 46: 426-430.
Direct Link |
5: Davey, N.P., M.E. Anderson and D.A. James, 2005. An accelerometer-based system for elite athlete swimming performance analysis. Proc. SPIE, 5649: 409-415.
CrossRef | Direct Link |
6: Inoue, Y., T. Kimura, S. Fujita, H. Noro and K. Nishikawa et al 2003. A new parameter for assessing postoperative recovery of physical activity using an accelerometer. Surg. Today, 33: 645-650.
7: Jaecques, S.V.N., N.J.B. Driessen, L. Havermans, B. Daenen, I. Denayer, F. Burny and G. Van der Perre, 2003. Vibration analysis of orthopaedic implant stability. Acta Bioeng. Biomech., 4: 194-195.
Direct Link |
8: Kavanagh, J., S. Morrison, D.A. James and R. Barrett, 2006. Reliability of segmental accelerations measured using a new wireless gait analysis system. J. Biomech., 39: 2863-2872.
9: Kellis, E. and A. Katis, 2007. Biomechanical characteristics and determinants of instep soccer kick. J. Sport. Sc. Med., 6: 154-165.
Direct Link |
10: Lees, A. and L. Nolan, 1998. The biomechanics of soccer: A review. J. Sport. Sci., 16: 211-234.
CrossRef | PubMed |
11: Mathie, M.J., A.C.F. Coster, N.H. Lovell and B.G. Celler, 2004. Accelerometry: providing an integrated, practical method for long-term, ambulatory monitoring of human movement. Physiol. Meas., 25: R1-R20.
12: McMillan, K., J. Helgerud, R. Macdonald and J. Hoff, 2005. Physiological adaptations to soccer specific endurance training in professional youth soccer players. Br. J. Sports Med., 39: 273-277.
13: Meamarbashi, A. and Y.M. Burhanuddin, 2006. MEMS triaxial accelerometer for physical activity monitoring. Proceedings of the Asia-Pacific Conference of Transducers and Micro-nano Technology, June 25-28, 2006, Nanyang Technological University, Singapore, pp: 249-252.
14: Najafi, B., K. Aminian, F. Loew, Y. Blanc and P.A. Robert, 2002. Measurement of stand-sit and sit-stand transitions using a miniature gyroscope and its application in fall risk evaluation in the elderly. IEEE Trans. Biomed. Eng., 49: 843-851.
15: Ohgi, Y., H. Ichikawa and C. Miyaji, 2002. Microcomputer-based acceleration sensor device for swimming stroke monitoring. JSME Int. J. Series C, 45: 960-966.
CrossRef | Direct Link |
16: Ohgi, Y. and M. Yasumura, 2000. In the Engineering of Sport Research, Development and Innovation. Blackwell Science, Oxford, pp. 503-511.
17: Salarian, A., H. Russmann, F.J.G. Vingerhoets, C. Dehollain, Y. Blanc, P.R. Burkhard and K. Aminian, 2004. Gait Assessment in Parkinson’s Disease: Toward an Ambulatory System for Long-Term Monitoring. IEEE Trans. Biomed. Eng., 51: 1434-1443.
CrossRef | Direct Link |
18: Scapellato, S., F. Cavallo, C. Martelloni and A.M. Sabatini, 2005. In-use calibration of body-mounted gyroscopes for applications in gait analysis. J. Sens. Actuators A: Physical, 418: 123-124.
19: Taylor, N.A.S., R.H. Sanders, E.L. Howick and S.N. Stanley, 1991. Static and dynamic assessment of the Biodex dynamometer. Eur. J. Appl. Physiol., 62: 180-188.
20: Willemsen, A.T.M., J.A. van Alsté and H.B.K. Boom, 1990. Real-time gait assessment utilizing a new way of accelerometry. J. Biomech., 23: 859-859.
21: Xsens, 2007. Human Motion Sensor. http://www.xsens.com/index.php?mainmenu=products&submenu=human_motion
22: Tan, C.W. and S. Park, 2002. Design and error analysis of accelerometer-based inertial navigation systems. California partners for advanced transit and highways (PATH). Research Reports: Paper UCB-ITS-PRR-2002-21. http://repositories.cdlib.org/cgi/viewcontent.cgi?article=1563&context=its/path.
23: MEMSENSE, 2007. The nano IMU (nIMU). http://www.memsense.com/images/downloads/65/Datasheet-v2.11.pdf.
24: Nevalainen, E., 2008. Accelerometer configurations for a gyroscope free inertial navigation system. Helsinki University of Technology, Faculty of Information and Natural Sciences, Helsinki, pp: 28. http://www.sal.tkk.fi/Opinnot/Mat-2.108/pdf-files/enev08.pdf.
25: Park, S., C.W. Tan and J. Park, 2005. A scheme for improving the performance of a gyroscope-free inertial measurement unit. Sensors Actuators A: Phys., 121: 410-420.
CrossRef | Direct Link |