Bio-Medical Materials and Engineering 24 (2014) 297–306 DOI 10.3233/BME-130811 IOS Press
297
Characteristic Analysis of the Lower Limb Muscular Strength Training System applied with MR Dampers Chang Ho Yu a, Young Jun Piaob, Kyung Kimb and Tae Kyu Kwon a,c* a
Division of Biomedical Engineering, Chonbuk National University, Deokjin-Dong 1-Ga, Jeonju, Jeonbuk 561-756,South Korea b Chonbuk National University Automobile-Parts &Mold Technology Innovation Center, Jeonju, Jeonbuk 561-844,South Korea c Bioengineering Research Center for the Aged, Chonbuk National University, Jeonju, Jeonbuk 561756, South Korea
Abstract. A new training system that can adjust training intensity and indicate the center pressure of a subject was proposed by applying controlled electric current to the Magneto-Rheological damper. The experimental studying on the muscular activities were performed in lower extremities during maintaining and moving exercises, which were processed on an unstable platform with Magneto rheological dampers and recorded in a monitor. The electromyography (EMG) signals of the eight muscles in lower extremities were recorded and analyzed in certain time and frequency domain., Muscles researched in this paper were rectus femoris (RF), biceps femoris (BF), tensor fasciae latae (TFL), vastuslateralis (VL), vastusmedialis (VM), gastrocnemius (Ga), tibialis anterior (TA), and soleus (So). Differences of muscular activities during four moving exercises were studied in our experimental results. The rate of the increment of the muscular activities was affected by the condition of the unstable platform with MR dampers, which suggested the difference of moving exercises could selectively train each muscle with varying intensities. Furthermore, these findings also proposed that this training system can improve the ability of postural balance. Keywords: Muscular activities, magneto-rheological damper, unstable platform
1. Introduction Postural balance is essential for the stability and independence of human body, which is accomplished by composing and executing the positions or motions of a human body within a space against a given gravity and environment in a central nervous system by using the peripheral information collected from visual, somatosensory, and vestibular systems[1]. In the maintenance of postural balance, muscular characteristics (muscular strength) play important role as well as musculoskeletal functions of joint movement range and flexibility of spine in sensory and nervous systems. The muscular strength is defined as the maximum tension that can be exercised without changing muscle length. *Corresponding author. E-mail: [email protected] 0959-2989/14/$27.50 © 2014 – IOS Press and the authors. All rights reserved
298
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
The reduction of muscular strength is one of the major reasons limiting physical activity in the aged and instigating amyotrophy or reduction of bone density in exercise deficient aged people. Thus, they often have to face handicaps in daily life due to the acute reduction of physical powers, which is often discussed in the categories of muscular strength, flexibility, agility and balancing capacity [2]. In the study of muscular strength training, Mohammod [3] analyzed the effect of muscular strength training in vestibular, visual and musculoskeletal system using gymnastics 60 minutes a day for 12 weeks, which found the increment of balancing stability and muscular strength in lower extremities of the aged during training. Kim et al. [4][5] studied an effect of muscular strength training of lower extremities in the aged by stand-up balancing, and also reviewed the effect of the incremental muscular strength training in the aged. The improvement of balancing power and reduction of injuries in a fall were stated by Jennifer and Hess et al., which found that the 10 weeks muscular strength training of quadriceps femoris, hamstring tendon, tibialis anterior, soleus muscles would improve Berg Balance Scale, Time up and Go and Activities-Specific Balance Confidence Scale of test subjects[6]. Rogers [7] reported that the 16 weeks of rubber band training significant improved grasping power and muscular strength of lower extremities. On the study of postural balance and the muscular strength by using an unstable platform, Ivanenko et al. [9] reported the effect of postural balance on an unstable platform with the reaction force of a foot support, and Piao et al. [10] analyzed the effect of a postural balance training in the aged or patients with balancing dysfunction due to the loss or injury of balancing power through the quantitative analysis of balance sensing training using an unstable platform. Among the muscular strength methods reported so far, the periodic training methods by using the commercialized health machines (Hammer strength etc.) and rehabilitation devices (Biodex, Maxicam, Cybex etc.) have been reported along with the methods of repeating resistance gymnastics and the application of rubber bands in resistance training [3-8]. Previously, these types of training caused many complications in the aged but the benefits disregarded. However, positive effects of muscular strength training in the improvement of health have been spotlighted nowadays. So, the health issues of the aged have to be handled by reducing chronic disease exacerbation, maintaining and improving the muscular strength function [11-17]. Such muscular strength training using gymnastics is one-directional training methods that can’t feedback the real muscular strength of a trainee. Moreover, it could be difficult for a trainee to have a motivation to perform training due to the repetition of simple postures, and there are problems of spatial consumption in system establishment as well as setting up expensive equipment in case of adopting health and rehabilitation. By monitoring the slide of a platform in real time basis, this study controlled the muscular activation state through the control of damping force in magneto-rheological (MR) fluid damper. In addition, monitoring the orbital movement of body shift was also assigned to figure out the more effective muscular strength training system, and movement program was executed to review the muscular characteristics of lower extremities in this system and to find the quantification method of determining which muscles could be activated by a specific training method. 2. Experimental methods 2.1. Muscular strength training system applied with MR dampers Figure 1(a) shows the unstable platform system attached with MR dampers, which is comprised of an unstable platform and a training monitoring unit. The system that we developed [20] was designed with a MR damper controller adjusting the damping grade, a stable unit frame installed for the safety
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
299
of a training subject, an unstable platform attached with MR dampers, a lower supporting structure for the unstable platform, and a training monitor providing visual stimulation. The MR dampers applied unstable platform was equipped with two tilt sensors to measure the tilt angle of the platform. To determine the size, shape, and measurement principle of an unstable platform, this study investigated the mechanism of balancing organs related to postural balance and several stimulation devices previously reported. Based upon the investigation results, the size of an unstable platform was determined to have a circular shape with the diameter of 500 mm and thickness of 20 mm.
Fig. 1.(a) Training system using an unstable platform with Magneto-Rheological dampers. (b) Unstable platform with Magneto-Rheological dampers
The MR damper is a type of semi-active control device using fine magnetic particles in MR fluid, which flows freely like a common viscous fluid in normal circumstance. However, magnetic force aligns the particles quickly to limit the flow of the fluid, which generates the yield strength eventually. So, the MR damper could change the attenuation characteristics of the damper by controlling the MR fluid using a magnetic field. To measure the slide of left and right balance, two tilt sensors (SA1, DAS technology Co.) were used to output the corresponding slide changing signals of the unstable platform according to the movement of a testing subject, with the maximum slide angle of 14. The size of the external type of MR damper controller was 180mm × 80mm × 70mm (L × W × H) with a power button, a controller to control the volume level of output in 4 dampers, and 4 LCD lights indicating the input mode, frequency, duty rate, and current output. Since the damper controller controls the current supplied to the damper, a constant current output system with a frequency of 33 KHz was applied for comparison of the high response characteristics of the MR damper. The damping force of the MR damper was controlled based upon the intensity of withdrawing current. The voltage and output current of the controller was set to DC 12Volt and 0~2A along with the installation of a RS232C port, which enabled the communication with other equipment. The current of damping characteristics could be found at the Technical data of RD-1005-3 MR damper of Lord Co. [18]. Figure 1(b) shows the platform attached with the MR damper, the upper platform is the basic component for stand, and the lower platform is connected to supporting unit of the upper platform, which is comprised of rolling part to maintain the center of the unstable platform, 4 MR dampers located at the lower supporting part with 90 interval, spring, and the lower supporting part. Several damper fixing jigs were installed between the unstable platform and the lower supporting part to fix each damper.
300
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
2.2. Software for the muscular strength training Figure 2 shows the movement training program, which traced the target that kept body balance on an unstable platform. The target makes the movement in anterior-posterior (AP) and left-right (LR) direction by 45 and -45, respectively for 32 seconds, and a test subject followed the target.
Fig. 2. Program for the excises of moving body shift : (a) Anterior-posterior direction (b) Left-right direction (c) 45° direction (d) -45° direction
G Fig. 3. Examples of monitoring training during moving exercise.
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
301
Figure 3 shows the monitoring example of moving exercise. The monitoring device shows the body shift of a test subject by the measurement of unstable platform slide in real time during the training. This suggested body shift helps the test subject to execute the task, and the task performance capacity is represented through the body shift orbit. 2.3. Subjects The present study was conducted by 5 male and 5 female subjects with right dominant foot at mean age of 26.8 years old. Since the test subjects did not have any periodic muscular strengthening exercise for the last 1 year, none of them have musculoskeletal or neuromuscular systematic injuries. To conform to the Declaration of Helsinki (1964), written informed consent was obtained from all subjects. 2.4. Data collection and analysis The measurement of muscular strength was made by using the MP150 (BIOPAC system, Inc.) with the sampling rate of 1000 and amplification rate of 1000. To filter the electromyographic signals, the 5 – 500Hz of band pass filter including the electromyographic signals of 20 - 300Hz was used. The circular shaped electrodes (EL500, BIOPAC System, Inc.) with the diameter of20 mm were attached after the keratinous skin layer removed, which used sterilization alcohol to reduce the skin resistance against the surface. The measurement muscles of moving exercise included the rectus femoris (RF), biceps femoris (BF), tensor fasciae latae (TFL), vastuslateralis (VL), vastusmedialis (VM), gastrocnemius (Ga), tibialis anterior (TA), and Soleus (So) in right leg of the dominant foot. During the moving exercise, if the average distance between the center of target circle and the body shift of a test subject was smaller than the radius of a target circle, the performance was regarded as the satisfactory one that can be used in data analysis. Although the EMG signals collected from surface electrodes included many information related to several units of action potential, there are overlapped random frequencies depended upon the characteristics of muscle type. So, current study used the varying probability of statistical analysis method in a view plane and frequency plane. The measured EMG signals collected from a test subject was standardized as the common normal signal by using the mean dynamic activity (m-DYN) method to compare with the EMG signals collected from other test subjects [19]. The standardized EMG signals were conducted for the frequency analysis using the FFT, and the probability density function was earned to calculate the spectral energy to know the muscular activity. The One-way ANOVA and Paired t-tests were conducted to analyze the significance of the test result by using a SPSS 12.0 statistical program. 2.5. Experimental protocol To review the muscular strength characteristics in this system, the current that controlled the instability of platform was supplied with 0mA, 50mA, and 100mA in maintaining and moving exercises. By applying the current on unstable platform, the exercise program was progressed from the moving exercise program as shown in Figure 2. When each exercise program was performed, the body shift movement orbit of a test subject could be confirmed in a real time basis by using training monitoring equipment. To prevent the muscular injury caused by abrupt training, 5 minute pre-training exercise was performed before training. After pre-training exercise, the suggested training displayed in a monitor was performed. All training including 4 patterns of moving exercises were randomly selected to exclude
302
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
the learning effect through the adaptation. The moving exercises were performed with two interval rests of 2 minutes considering the development of fatigue by the training. 3. Results and discussion 3.1. Muscular activation in the moving training Figure 4 represents the muscular activation of a muscle displayed in a frequency plane at the moving exercise for 32 seconds according to each pattern from the center. The abscissa indicates the muscle attached with electrodes and the ordinate indicates the spectral energy that expresses the muscular activation. In all patterns, six muscles excluding the VM and So were activated by increasing the supplied current. Namely, the muscular activation is changed by the control of supplied current in performing the same exercise. In the reviewing pattern, the BF (p=0.049), Ga (p=0.001), and TA (p=0.003) revealed high muscular activation in anterior-posterior pattern, while the BF (p=0.001), TFL (p=0.030) and Ga (p=0.000) were activated in left-right pattern. In the 45 and -45 pattern, the BF (p=0.013, p=0.001), TFL (p=0.001, p=0.001), Ga (p=0.001, p=0.001) and TA (p=0.003, p=0.001) indicated the high muscular activation, and the muscles of So and VM revealed low muscular activation recording less than 0.001V2. The muscular activation of BF and Ga muscles were high in all patterns. The TA muscle was especially high in anterior-posterior pattern, while TFL was highest in left-right pattern, while the TFL and TA muscles were moreactive in 45 and -45 pattern as shown in Figure 5.
Fig. 4.Spectral energy of the EMG signals in different muscles for different movement exercises: (a) Movement in AP direction (b) Movement in LR direction (c) Movement in 45° direction (d) Movement in -45 ° direction
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
303
Comparing the results in Figure 5(a), it is suggested that the muscular activation of left-right pattern is lower than anterior-posterior pattern, and the execution in platform pushing of left-right pattern was easier than the anterior-posterior pattern. This could be related to the fact that the posture of test subject feet was opened to the width of shoulder, which paralleled to right and left sides during the training. The movement of body shift during the left-right pattern is easier than anterior-posterior pattern. In addition, the psychological discomfort of maintaining the platform pushing backwardin the leftright pattern should be considered. The muscular activation in 45 was found higher than in -45 as shown in Figure 5(b). Although the 45 and -45 patterns have a symmetric relationship, the right foot was primarily used in the 45 pattern since all test subjects had right dominant foot, and the left foot was primarily used in -45 pattern. In addition, the increment rates of muscular activation at the current of 50mA and 100mA were calculated by comparing the spectral energyacquired in 0mA.Overall mean increment rate of all muscles was 8.4% (p=0.004)at the current of 50mA in anterior-posterior pattern, and 14.2% (p=0.021) was recorded in 100mA. The rates recorded at the current of 50mA and 100mA in 45 pattern were6.8% (p=0.040) and 13.5% (p=0.069), and 2.7% (p=0.003) and 2.9% (p=0.001) in -45 pattern, respectively. The observed results of the muscular activation and the increment rate of muscular activation in moving exercise show the difference of muscles in varied patterns. This indicated that muscular activation of test subjects could be controlled by adjusting the supplied current leveland its increment rate depend upon the pattern, which implies the possibility of applying the result for more efficient muscular strength training.
Fig. 5.Spectral energy of the EMG signals from four different muscles for different moving exercises: (a) BF (b) TFL (c) Ga (d) TA
Figure 6 displayed the muscular activation of musclesof each pattern. The abscissa indicates the exercise direction of patterns and the ordinate indicates the moving average filtered EMG signal of the
304
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
EMG activation. The Ga muscle was found to have the highest muscular activation in all patterns. The anterior-posterior patternsin the moving exercise indicated the activation of the Ga and So muscles by moving from the center to the anterior direction or from the posterior position to the center. The muscular activation of the BF muscle was intensified when moving from center to the posterior direction and gradually weakened back to the center. When moving from the anterior position to the center and from the center to the posterior direction, the activation of the RF, TFL, VL, and TA was increasing. This could be attributed to the activation of the Ga and So muscles related to the plantar flexion in the anterior movement. At the same time, the BFmuscles which affects the crus and ankle was activated, and the quadriceps femoris (QF) and TFL muscles controlled the stand up posture were activated in the posterior movement, and the TA muscles responded to the body slide to backward direction through relaxation and contraction of muscular. In the left-right pattern, the Ga muscle was activated when moving from the center to the right direction and from the left to the center. The muscular activation of the RF, TFL, BF, and VL was slowly increased when moving from the center to the left, and maintained the levelback to the center. Themovement of left-right direction, which had the smaller muscular variation in each muscle, was founded easier compared with the anterior-posterior direction, and several muscles were also activated when moving from the left to the center. It is considered that postural control in left-right pattern is mainly controlled by the muscles in a femur due to the center of gravity does not move either anterior or posterior compared with other patterns.
Fig. 6.Moving average filtered EMG of EMG signals in various muscles for different moving exercises: (a) AP direction (b) LR direction (c) 45° direction (d) -45° direction
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
305
As results of overall muscular activation represented in Figure 4, the 45 and -45 patterns have to consider the effect of attached electrode positions and dominant foot of test subjects. In the 45 pattern, the Ga and TA muscles’ muscular activations were found to be higher. The muscular activation of Ga muscle largely increased when moving from the center to the right direction and decreased to the posterior-left direction, but it increased again when back to the center. Namely, the muscular activation of the Ga increased when the force inclined into frontal direction. The muscular activation of the TA largely increasedsince the position of the center of gravity was closer to the foot heel when the muscle moves from the center to the posterior-left direction, and decreased as it return back to the center. The RF, TFL and VL muscles showed the slightly increase of the muscular activation when moving from the anterior-right position to the center, which was similarly from the posterior-left position to the center. In the -45 pattern, the muscular activation tendency of the Ga and BF was comparable to the muscular activation tendency in the RF, TFL, VL, and TA muscles. When moving from the posterior-left position to the anterior-left direction, the Ga and BF muscles were activated, but other muscles were activated when moving from the center to the posterior-right direction and from the anteriorleft position to the center. The muscles located in anterior part of a body was activated by the motions moving the center of a body forward, and the motions moving the center of a body backward activated the muscles located in the posterior part. Based upon previous results, the various muscular activation patterns were confirmed depend upon the patterns of moving exercise and the supplied current to the unstable platform. This may be applied in performing the efficient muscular strength training by the pattern of the moving exercise varied by the damping force of the unstable platform 4. Conclusion The present study conducted the movingexercise on the MR damper applied the unstable platform to seek an efficient and quantitative muscular strength training method, and the quantitative review was made to figure out which muscle could be activated during each exercise. 1. In the movingexercise, each muscle shown different muscular activation and muscular activation increment rate depend upon the pattern, direction, and the volume of supplied current. 2. In the anterior-posterior pattern and left-right pattern, the TA and TFL muscles were highly activated, respectively. However, the TFL was rather higher activated compared to TA muscle in 45 and 45 pattern, and the current supplied to the unstable platform affected the increment rate of muscular activation. 3. The MR damper applied unstable platform system was able to apply in the tailor made muscular strength training which can selectively train specific muscles of test subjects based on the moving patterns. 5. Acknowledgment This work was supported by Ministry of Knowledge Economy (QoLT Technology Development, No. 10036494) and also supported by the Sports Promotion Fund of Seoul Olympic Sports Promotion Foundation from Ministry of Culture, Sports and Tourism in 2013.
306
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]
A. Shumway-Cook and M. Wollacott, Motor control: Theory and practical applications, 4thed, Baltimore: Williams &Willkins, 2001. J.V. Jessup, C. Horne, R.K. Vishen and D. Wheeler, Effects of exercise on bone density, balance, and self-efficacy in older woman, Biological Research for Nursing 4 (2003),171-180. M.I. Mohammod, E. Nasu, M.E. Rogers, D. Koizumi, N.L. Rogers and N.Takeshima, Effects of combined sensory and muscular training on balance in Japanese older adults, Preventive Medicine 39 (2004),1148-1155. T.H. Kimand D.S. Oh, Effects of exercise training on strength and balance for the elderly, Korean Academy of University Trained Physical Therapists 7 (2004), 32-37. H.S. Kim, The effect of progressive exercise on the activities of the elderly, Korean Academy of University Trained Physical Therapists 7(2000), 19-33. J.A. Hess and M. Wollacott, Effect of high-intensity strength-training on functional measures of balance ability in balance-impaired older adults, Journal of Manipulative and Physiological Therapeutics 28(2005), 582-590. M.E. Rogers, N.L. Rogers, N. Takeshima and M.M. Islam, Method to assess and improve the physical parameters associated with fall risk in older adults, Preventive Medicine 36(2003), 255-264. R.D. Seidler and P.E. Martin, The effects of short term balance training on the postural control of older adults, Gait & Posture 6(1997), 224-236. Y.P. Ivanenko, I.A. Solopova and Y.S. Levik, The direction of postural instability affects postural reactions to ankle muscle vibration in humans, Neuroscience Letters 292 (2000), 103-109. Y.J. Piao, M. Yu, T.K. Kwon, J.H. Hwang and N.G. Kim NG, Quantitative analysis of the training of equilibrium sense for the elderly using an unstable platform, Journal of Biomedical Engineering Research 28(2007), 410-416. J.W. Webster andJ.W. Clark, Medical instrumentation-application and design, 2nded, Houghton Mifflin Co, 1992, p. 150-2211. U. Kuruganti, P. Parker, J. Rickards and M.Tingley, Strength and muscle coactivation in older adults after lower limb strength training, International Journal of Industrial Ergonomics 36(2006), 761-766. C.M. Hall and L.T. Brody, Therapeutic exercise-moving toward function, Washington: Lippincott Williams & Wilkins inc, 2004, pp.139-155. D.A. Neumann, Kinesiology of the musculoskeletal system, Wisconsin: Elsevier, 2002. pp. 45-59. G.L. Almeida, R.L. Carvalho and V.L.Talis, Postural strategy to keep balance on the seesaw, Gait & Posture 23(2006), 17-21. L.M. Latash, Neurophysiological basis of movement, Pennsylvania : Human kinetics, 1998. pp. 50, 69, 193-202. B.D. Jenkins, Functional anatomy of the limbs and back, Illinois: W. B. SAUNDERS Co, 1999, pp. 347-389. LORD Technical Date, RD-1005-3 Damper://www.lord.com. L.A. Bolala, T.L. Uhl, Reliability of electromyographic normalization methods for evaluating the hip musculature, Journal of Electromyography and Kinesiology 17 (2007), 102-111. Y.J. Choi, Y.J. Piao, M. Heo, T.K. Kwon, J.H. Hwang, D.W. Kim and N.G. Kim, Development of rehabilitation training system using unstable flatform with magneto-rheological damper, Journal of Institute of Control, Robbtics and System 14 (2008), 197~204.
Copyright of Bio-Medical Materials & Engineering is the property of IOS Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
297
Characteristic Analysis of the Lower Limb Muscular Strength Training System applied with MR Dampers Chang Ho Yu a, Young Jun Piaob, Kyung Kimb and Tae Kyu Kwon a,c* a
Division of Biomedical Engineering, Chonbuk National University, Deokjin-Dong 1-Ga, Jeonju, Jeonbuk 561-756,South Korea b Chonbuk National University Automobile-Parts &Mold Technology Innovation Center, Jeonju, Jeonbuk 561-844,South Korea c Bioengineering Research Center for the Aged, Chonbuk National University, Jeonju, Jeonbuk 561756, South Korea
Abstract. A new training system that can adjust training intensity and indicate the center pressure of a subject was proposed by applying controlled electric current to the Magneto-Rheological damper. The experimental studying on the muscular activities were performed in lower extremities during maintaining and moving exercises, which were processed on an unstable platform with Magneto rheological dampers and recorded in a monitor. The electromyography (EMG) signals of the eight muscles in lower extremities were recorded and analyzed in certain time and frequency domain., Muscles researched in this paper were rectus femoris (RF), biceps femoris (BF), tensor fasciae latae (TFL), vastuslateralis (VL), vastusmedialis (VM), gastrocnemius (Ga), tibialis anterior (TA), and soleus (So). Differences of muscular activities during four moving exercises were studied in our experimental results. The rate of the increment of the muscular activities was affected by the condition of the unstable platform with MR dampers, which suggested the difference of moving exercises could selectively train each muscle with varying intensities. Furthermore, these findings also proposed that this training system can improve the ability of postural balance. Keywords: Muscular activities, magneto-rheological damper, unstable platform
1. Introduction Postural balance is essential for the stability and independence of human body, which is accomplished by composing and executing the positions or motions of a human body within a space against a given gravity and environment in a central nervous system by using the peripheral information collected from visual, somatosensory, and vestibular systems[1]. In the maintenance of postural balance, muscular characteristics (muscular strength) play important role as well as musculoskeletal functions of joint movement range and flexibility of spine in sensory and nervous systems. The muscular strength is defined as the maximum tension that can be exercised without changing muscle length. *Corresponding author. E-mail: [email protected] 0959-2989/14/$27.50 © 2014 – IOS Press and the authors. All rights reserved
298
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
The reduction of muscular strength is one of the major reasons limiting physical activity in the aged and instigating amyotrophy or reduction of bone density in exercise deficient aged people. Thus, they often have to face handicaps in daily life due to the acute reduction of physical powers, which is often discussed in the categories of muscular strength, flexibility, agility and balancing capacity [2]. In the study of muscular strength training, Mohammod [3] analyzed the effect of muscular strength training in vestibular, visual and musculoskeletal system using gymnastics 60 minutes a day for 12 weeks, which found the increment of balancing stability and muscular strength in lower extremities of the aged during training. Kim et al. [4][5] studied an effect of muscular strength training of lower extremities in the aged by stand-up balancing, and also reviewed the effect of the incremental muscular strength training in the aged. The improvement of balancing power and reduction of injuries in a fall were stated by Jennifer and Hess et al., which found that the 10 weeks muscular strength training of quadriceps femoris, hamstring tendon, tibialis anterior, soleus muscles would improve Berg Balance Scale, Time up and Go and Activities-Specific Balance Confidence Scale of test subjects[6]. Rogers [7] reported that the 16 weeks of rubber band training significant improved grasping power and muscular strength of lower extremities. On the study of postural balance and the muscular strength by using an unstable platform, Ivanenko et al. [9] reported the effect of postural balance on an unstable platform with the reaction force of a foot support, and Piao et al. [10] analyzed the effect of a postural balance training in the aged or patients with balancing dysfunction due to the loss or injury of balancing power through the quantitative analysis of balance sensing training using an unstable platform. Among the muscular strength methods reported so far, the periodic training methods by using the commercialized health machines (Hammer strength etc.) and rehabilitation devices (Biodex, Maxicam, Cybex etc.) have been reported along with the methods of repeating resistance gymnastics and the application of rubber bands in resistance training [3-8]. Previously, these types of training caused many complications in the aged but the benefits disregarded. However, positive effects of muscular strength training in the improvement of health have been spotlighted nowadays. So, the health issues of the aged have to be handled by reducing chronic disease exacerbation, maintaining and improving the muscular strength function [11-17]. Such muscular strength training using gymnastics is one-directional training methods that can’t feedback the real muscular strength of a trainee. Moreover, it could be difficult for a trainee to have a motivation to perform training due to the repetition of simple postures, and there are problems of spatial consumption in system establishment as well as setting up expensive equipment in case of adopting health and rehabilitation. By monitoring the slide of a platform in real time basis, this study controlled the muscular activation state through the control of damping force in magneto-rheological (MR) fluid damper. In addition, monitoring the orbital movement of body shift was also assigned to figure out the more effective muscular strength training system, and movement program was executed to review the muscular characteristics of lower extremities in this system and to find the quantification method of determining which muscles could be activated by a specific training method. 2. Experimental methods 2.1. Muscular strength training system applied with MR dampers Figure 1(a) shows the unstable platform system attached with MR dampers, which is comprised of an unstable platform and a training monitoring unit. The system that we developed [20] was designed with a MR damper controller adjusting the damping grade, a stable unit frame installed for the safety
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
299
of a training subject, an unstable platform attached with MR dampers, a lower supporting structure for the unstable platform, and a training monitor providing visual stimulation. The MR dampers applied unstable platform was equipped with two tilt sensors to measure the tilt angle of the platform. To determine the size, shape, and measurement principle of an unstable platform, this study investigated the mechanism of balancing organs related to postural balance and several stimulation devices previously reported. Based upon the investigation results, the size of an unstable platform was determined to have a circular shape with the diameter of 500 mm and thickness of 20 mm.
Fig. 1.(a) Training system using an unstable platform with Magneto-Rheological dampers. (b) Unstable platform with Magneto-Rheological dampers
The MR damper is a type of semi-active control device using fine magnetic particles in MR fluid, which flows freely like a common viscous fluid in normal circumstance. However, magnetic force aligns the particles quickly to limit the flow of the fluid, which generates the yield strength eventually. So, the MR damper could change the attenuation characteristics of the damper by controlling the MR fluid using a magnetic field. To measure the slide of left and right balance, two tilt sensors (SA1, DAS technology Co.) were used to output the corresponding slide changing signals of the unstable platform according to the movement of a testing subject, with the maximum slide angle of 14. The size of the external type of MR damper controller was 180mm × 80mm × 70mm (L × W × H) with a power button, a controller to control the volume level of output in 4 dampers, and 4 LCD lights indicating the input mode, frequency, duty rate, and current output. Since the damper controller controls the current supplied to the damper, a constant current output system with a frequency of 33 KHz was applied for comparison of the high response characteristics of the MR damper. The damping force of the MR damper was controlled based upon the intensity of withdrawing current. The voltage and output current of the controller was set to DC 12Volt and 0~2A along with the installation of a RS232C port, which enabled the communication with other equipment. The current of damping characteristics could be found at the Technical data of RD-1005-3 MR damper of Lord Co. [18]. Figure 1(b) shows the platform attached with the MR damper, the upper platform is the basic component for stand, and the lower platform is connected to supporting unit of the upper platform, which is comprised of rolling part to maintain the center of the unstable platform, 4 MR dampers located at the lower supporting part with 90 interval, spring, and the lower supporting part. Several damper fixing jigs were installed between the unstable platform and the lower supporting part to fix each damper.
300
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
2.2. Software for the muscular strength training Figure 2 shows the movement training program, which traced the target that kept body balance on an unstable platform. The target makes the movement in anterior-posterior (AP) and left-right (LR) direction by 45 and -45, respectively for 32 seconds, and a test subject followed the target.
Fig. 2. Program for the excises of moving body shift : (a) Anterior-posterior direction (b) Left-right direction (c) 45° direction (d) -45° direction
G Fig. 3. Examples of monitoring training during moving exercise.
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
301
Figure 3 shows the monitoring example of moving exercise. The monitoring device shows the body shift of a test subject by the measurement of unstable platform slide in real time during the training. This suggested body shift helps the test subject to execute the task, and the task performance capacity is represented through the body shift orbit. 2.3. Subjects The present study was conducted by 5 male and 5 female subjects with right dominant foot at mean age of 26.8 years old. Since the test subjects did not have any periodic muscular strengthening exercise for the last 1 year, none of them have musculoskeletal or neuromuscular systematic injuries. To conform to the Declaration of Helsinki (1964), written informed consent was obtained from all subjects. 2.4. Data collection and analysis The measurement of muscular strength was made by using the MP150 (BIOPAC system, Inc.) with the sampling rate of 1000 and amplification rate of 1000. To filter the electromyographic signals, the 5 – 500Hz of band pass filter including the electromyographic signals of 20 - 300Hz was used. The circular shaped electrodes (EL500, BIOPAC System, Inc.) with the diameter of20 mm were attached after the keratinous skin layer removed, which used sterilization alcohol to reduce the skin resistance against the surface. The measurement muscles of moving exercise included the rectus femoris (RF), biceps femoris (BF), tensor fasciae latae (TFL), vastuslateralis (VL), vastusmedialis (VM), gastrocnemius (Ga), tibialis anterior (TA), and Soleus (So) in right leg of the dominant foot. During the moving exercise, if the average distance between the center of target circle and the body shift of a test subject was smaller than the radius of a target circle, the performance was regarded as the satisfactory one that can be used in data analysis. Although the EMG signals collected from surface electrodes included many information related to several units of action potential, there are overlapped random frequencies depended upon the characteristics of muscle type. So, current study used the varying probability of statistical analysis method in a view plane and frequency plane. The measured EMG signals collected from a test subject was standardized as the common normal signal by using the mean dynamic activity (m-DYN) method to compare with the EMG signals collected from other test subjects [19]. The standardized EMG signals were conducted for the frequency analysis using the FFT, and the probability density function was earned to calculate the spectral energy to know the muscular activity. The One-way ANOVA and Paired t-tests were conducted to analyze the significance of the test result by using a SPSS 12.0 statistical program. 2.5. Experimental protocol To review the muscular strength characteristics in this system, the current that controlled the instability of platform was supplied with 0mA, 50mA, and 100mA in maintaining and moving exercises. By applying the current on unstable platform, the exercise program was progressed from the moving exercise program as shown in Figure 2. When each exercise program was performed, the body shift movement orbit of a test subject could be confirmed in a real time basis by using training monitoring equipment. To prevent the muscular injury caused by abrupt training, 5 minute pre-training exercise was performed before training. After pre-training exercise, the suggested training displayed in a monitor was performed. All training including 4 patterns of moving exercises were randomly selected to exclude
302
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
the learning effect through the adaptation. The moving exercises were performed with two interval rests of 2 minutes considering the development of fatigue by the training. 3. Results and discussion 3.1. Muscular activation in the moving training Figure 4 represents the muscular activation of a muscle displayed in a frequency plane at the moving exercise for 32 seconds according to each pattern from the center. The abscissa indicates the muscle attached with electrodes and the ordinate indicates the spectral energy that expresses the muscular activation. In all patterns, six muscles excluding the VM and So were activated by increasing the supplied current. Namely, the muscular activation is changed by the control of supplied current in performing the same exercise. In the reviewing pattern, the BF (p=0.049), Ga (p=0.001), and TA (p=0.003) revealed high muscular activation in anterior-posterior pattern, while the BF (p=0.001), TFL (p=0.030) and Ga (p=0.000) were activated in left-right pattern. In the 45 and -45 pattern, the BF (p=0.013, p=0.001), TFL (p=0.001, p=0.001), Ga (p=0.001, p=0.001) and TA (p=0.003, p=0.001) indicated the high muscular activation, and the muscles of So and VM revealed low muscular activation recording less than 0.001V2. The muscular activation of BF and Ga muscles were high in all patterns. The TA muscle was especially high in anterior-posterior pattern, while TFL was highest in left-right pattern, while the TFL and TA muscles were moreactive in 45 and -45 pattern as shown in Figure 5.
Fig. 4.Spectral energy of the EMG signals in different muscles for different movement exercises: (a) Movement in AP direction (b) Movement in LR direction (c) Movement in 45° direction (d) Movement in -45 ° direction
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
303
Comparing the results in Figure 5(a), it is suggested that the muscular activation of left-right pattern is lower than anterior-posterior pattern, and the execution in platform pushing of left-right pattern was easier than the anterior-posterior pattern. This could be related to the fact that the posture of test subject feet was opened to the width of shoulder, which paralleled to right and left sides during the training. The movement of body shift during the left-right pattern is easier than anterior-posterior pattern. In addition, the psychological discomfort of maintaining the platform pushing backwardin the leftright pattern should be considered. The muscular activation in 45 was found higher than in -45 as shown in Figure 5(b). Although the 45 and -45 patterns have a symmetric relationship, the right foot was primarily used in the 45 pattern since all test subjects had right dominant foot, and the left foot was primarily used in -45 pattern. In addition, the increment rates of muscular activation at the current of 50mA and 100mA were calculated by comparing the spectral energyacquired in 0mA.Overall mean increment rate of all muscles was 8.4% (p=0.004)at the current of 50mA in anterior-posterior pattern, and 14.2% (p=0.021) was recorded in 100mA. The rates recorded at the current of 50mA and 100mA in 45 pattern were6.8% (p=0.040) and 13.5% (p=0.069), and 2.7% (p=0.003) and 2.9% (p=0.001) in -45 pattern, respectively. The observed results of the muscular activation and the increment rate of muscular activation in moving exercise show the difference of muscles in varied patterns. This indicated that muscular activation of test subjects could be controlled by adjusting the supplied current leveland its increment rate depend upon the pattern, which implies the possibility of applying the result for more efficient muscular strength training.
Fig. 5.Spectral energy of the EMG signals from four different muscles for different moving exercises: (a) BF (b) TFL (c) Ga (d) TA
Figure 6 displayed the muscular activation of musclesof each pattern. The abscissa indicates the exercise direction of patterns and the ordinate indicates the moving average filtered EMG signal of the
304
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
EMG activation. The Ga muscle was found to have the highest muscular activation in all patterns. The anterior-posterior patternsin the moving exercise indicated the activation of the Ga and So muscles by moving from the center to the anterior direction or from the posterior position to the center. The muscular activation of the BF muscle was intensified when moving from center to the posterior direction and gradually weakened back to the center. When moving from the anterior position to the center and from the center to the posterior direction, the activation of the RF, TFL, VL, and TA was increasing. This could be attributed to the activation of the Ga and So muscles related to the plantar flexion in the anterior movement. At the same time, the BFmuscles which affects the crus and ankle was activated, and the quadriceps femoris (QF) and TFL muscles controlled the stand up posture were activated in the posterior movement, and the TA muscles responded to the body slide to backward direction through relaxation and contraction of muscular. In the left-right pattern, the Ga muscle was activated when moving from the center to the right direction and from the left to the center. The muscular activation of the RF, TFL, BF, and VL was slowly increased when moving from the center to the left, and maintained the levelback to the center. Themovement of left-right direction, which had the smaller muscular variation in each muscle, was founded easier compared with the anterior-posterior direction, and several muscles were also activated when moving from the left to the center. It is considered that postural control in left-right pattern is mainly controlled by the muscles in a femur due to the center of gravity does not move either anterior or posterior compared with other patterns.
Fig. 6.Moving average filtered EMG of EMG signals in various muscles for different moving exercises: (a) AP direction (b) LR direction (c) 45° direction (d) -45° direction
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
305
As results of overall muscular activation represented in Figure 4, the 45 and -45 patterns have to consider the effect of attached electrode positions and dominant foot of test subjects. In the 45 pattern, the Ga and TA muscles’ muscular activations were found to be higher. The muscular activation of Ga muscle largely increased when moving from the center to the right direction and decreased to the posterior-left direction, but it increased again when back to the center. Namely, the muscular activation of the Ga increased when the force inclined into frontal direction. The muscular activation of the TA largely increasedsince the position of the center of gravity was closer to the foot heel when the muscle moves from the center to the posterior-left direction, and decreased as it return back to the center. The RF, TFL and VL muscles showed the slightly increase of the muscular activation when moving from the anterior-right position to the center, which was similarly from the posterior-left position to the center. In the -45 pattern, the muscular activation tendency of the Ga and BF was comparable to the muscular activation tendency in the RF, TFL, VL, and TA muscles. When moving from the posterior-left position to the anterior-left direction, the Ga and BF muscles were activated, but other muscles were activated when moving from the center to the posterior-right direction and from the anteriorleft position to the center. The muscles located in anterior part of a body was activated by the motions moving the center of a body forward, and the motions moving the center of a body backward activated the muscles located in the posterior part. Based upon previous results, the various muscular activation patterns were confirmed depend upon the patterns of moving exercise and the supplied current to the unstable platform. This may be applied in performing the efficient muscular strength training by the pattern of the moving exercise varied by the damping force of the unstable platform 4. Conclusion The present study conducted the movingexercise on the MR damper applied the unstable platform to seek an efficient and quantitative muscular strength training method, and the quantitative review was made to figure out which muscle could be activated during each exercise. 1. In the movingexercise, each muscle shown different muscular activation and muscular activation increment rate depend upon the pattern, direction, and the volume of supplied current. 2. In the anterior-posterior pattern and left-right pattern, the TA and TFL muscles were highly activated, respectively. However, the TFL was rather higher activated compared to TA muscle in 45 and 45 pattern, and the current supplied to the unstable platform affected the increment rate of muscular activation. 3. The MR damper applied unstable platform system was able to apply in the tailor made muscular strength training which can selectively train specific muscles of test subjects based on the moving patterns. 5. Acknowledgment This work was supported by Ministry of Knowledge Economy (QoLT Technology Development, No. 10036494) and also supported by the Sports Promotion Fund of Seoul Olympic Sports Promotion Foundation from Ministry of Culture, Sports and Tourism in 2013.
306
C.H. Yu et al. / Characteristic analysis of the lower limb muscular strength training system
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]
A. Shumway-Cook and M. Wollacott, Motor control: Theory and practical applications, 4thed, Baltimore: Williams &Willkins, 2001. J.V. Jessup, C. Horne, R.K. Vishen and D. Wheeler, Effects of exercise on bone density, balance, and self-efficacy in older woman, Biological Research for Nursing 4 (2003),171-180. M.I. Mohammod, E. Nasu, M.E. Rogers, D. Koizumi, N.L. Rogers and N.Takeshima, Effects of combined sensory and muscular training on balance in Japanese older adults, Preventive Medicine 39 (2004),1148-1155. T.H. Kimand D.S. Oh, Effects of exercise training on strength and balance for the elderly, Korean Academy of University Trained Physical Therapists 7 (2004), 32-37. H.S. Kim, The effect of progressive exercise on the activities of the elderly, Korean Academy of University Trained Physical Therapists 7(2000), 19-33. J.A. Hess and M. Wollacott, Effect of high-intensity strength-training on functional measures of balance ability in balance-impaired older adults, Journal of Manipulative and Physiological Therapeutics 28(2005), 582-590. M.E. Rogers, N.L. Rogers, N. Takeshima and M.M. Islam, Method to assess and improve the physical parameters associated with fall risk in older adults, Preventive Medicine 36(2003), 255-264. R.D. Seidler and P.E. Martin, The effects of short term balance training on the postural control of older adults, Gait & Posture 6(1997), 224-236. Y.P. Ivanenko, I.A. Solopova and Y.S. Levik, The direction of postural instability affects postural reactions to ankle muscle vibration in humans, Neuroscience Letters 292 (2000), 103-109. Y.J. Piao, M. Yu, T.K. Kwon, J.H. Hwang and N.G. Kim NG, Quantitative analysis of the training of equilibrium sense for the elderly using an unstable platform, Journal of Biomedical Engineering Research 28(2007), 410-416. J.W. Webster andJ.W. Clark, Medical instrumentation-application and design, 2nded, Houghton Mifflin Co, 1992, p. 150-2211. U. Kuruganti, P. Parker, J. Rickards and M.Tingley, Strength and muscle coactivation in older adults after lower limb strength training, International Journal of Industrial Ergonomics 36(2006), 761-766. C.M. Hall and L.T. Brody, Therapeutic exercise-moving toward function, Washington: Lippincott Williams & Wilkins inc, 2004, pp.139-155. D.A. Neumann, Kinesiology of the musculoskeletal system, Wisconsin: Elsevier, 2002. pp. 45-59. G.L. Almeida, R.L. Carvalho and V.L.Talis, Postural strategy to keep balance on the seesaw, Gait & Posture 23(2006), 17-21. L.M. Latash, Neurophysiological basis of movement, Pennsylvania : Human kinetics, 1998. pp. 50, 69, 193-202. B.D. Jenkins, Functional anatomy of the limbs and back, Illinois: W. B. SAUNDERS Co, 1999, pp. 347-389. LORD Technical Date, RD-1005-3 Damper://www.lord.com. L.A. Bolala, T.L. Uhl, Reliability of electromyographic normalization methods for evaluating the hip musculature, Journal of Electromyography and Kinesiology 17 (2007), 102-111. Y.J. Choi, Y.J. Piao, M. Heo, T.K. Kwon, J.H. Hwang, D.W. Kim and N.G. Kim, Development of rehabilitation training system using unstable flatform with magneto-rheological damper, Journal of Institute of Control, Robbtics and System 14 (2008), 197~204.
Copyright of Bio-Medical Materials & Engineering is the property of IOS Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
