- Email: [email protected]
The assessment of posture control in the elderly using the displacement of the center of pressure after forward platform translation
Journal of Electromyography and Kinesiology 11 (2001) 395–403 www.elsevier.com/locate/jelekin
The assessment of posture control in the elderly using the displacement of the center of pressure after forward platform translation H. Nakamura , T. Tsuchida , Y. Mano
*
Department of Rehabilitation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido, Japan Received 27 July 2000; received in revised form 23 February 2001; accepted 22 April 2001
Abstract We investigated the change of the center of pressure (COP) after forward platform translations in healthy subjects. These studies were performed on 26 normal young subjects and 20 healthy elderly subjects, who had a normal neurologic examination. Subjects stood barefoot on a three dimensional force plate on the platform, with feet parallel. The duration of the forward platform translations was 0.15 s, and the displacements were 3.75, 7.5, 10, 15, 20, and 30 mm. Six trials were carried out at random. The COP data were recorded for 35 s during standing, and were analyzed for 5 s after translation. With the platform translation displacements from 3.75 to 15 mm, displacement of the COP showed a tendency to increase in all subjects. Whereas with the stimuli between 20 and 30 mm, the results were more varied. The elderly group showed significantly (p⬍0.05) larger sway than the young group. These results indicate that the individual ability of posture control may be assessed by means of measuring the sway of the center of gravity after platform translation. Electromyography was carried out simultaneously, it showed that elderly people contrary to young subjects used proximal biceps femoris and distal foot muscles at an early stage of the platform translation (p⬍0.05), suggesting lack of ankle stability with aging. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Posture control; Platform translation; Center of pressure
1. Introduction Displacement of the center of pressure (COP) on a platform has been measured and used as an index of postural stability in standing. In 1929, it was first reported by Basler [1] who measured displacement of the COP. In following studies, the effects of age, sex, and other factors were determined [2–7]. As posturography is one of the tests of equilibrium, the displacement of the COP increased as an effect of aging. Also the relationship between the displacement of the COP and the strength of muscles was reported in Ref. [8]. With regard to the difference due to sex, the results of studies showed that the displacement of the COP for females was more unstable than males [3]. Moreover, in subsequent studies, corrective responses were observed by
* Corresponding author. Tel.: +81-11-706-6066; fax: +81-11-7066067. E-mail address: [email protected] (Y. Mano).
measurement of the COP with backward and forward platform translations and rotations [9–16]. Furthermore, there were many studies that measured electromyography (EMG) simultaneously in the lower limbs [17–24]. In experiments with cats [25–28], activation of thigh and foot muscles were observed as corrective responses to forward and backward translations, and the corrective responses for translations were investigated in quadrupedal stance and standing. Besides being reported in normal subjects, measurements of the COP were carried out in a variety of patients such as: bilateral peripheral vestibular deficits, diabetic peripheral neuropathy, Parkinson’s disease, and others [29–33]. Displacements of the COP were also measured to analyze the relationship between the stability of posture and falling. It is important to predict or prevent falling in the elderly. The elderly suffer injuries and their bones may fracture in a fall, and it often takes a long time for a complete recovery. What makes it even worse is that the injuries by falls prevent an active social life for the elderly, and this results in greater decline of body functions. There-
1050-6411/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 0 5 0 - 6 4 1 1 ( 0 1 ) 0 0 0 1 6 - 5
396
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
after the elderly may fall again. However it is difficult to exclude the effects of aging on the value of displacement of the COP in the existing quiet-standing test. Shumway-Cook and colleagues [34] investigated the effects of two different types of cognitive tasks on stability, as measured by COP displacement, in young versus older adults with and without a history of falls. Two cognitive tasks, a sentence completion and a visual perceptual matching task, were used to produce changes in attention during quiet stance under flat versus compliant surface conditions. While no differences were found between the young adults and the older healthy adults on a firm surface without a task, when the task complexity was increased, significant differences in postural stability between the two groups became apparent. In contrast to the young and healthy older adults, postural stability in older adults with a history of falls was significantly affected by both cognitive tasks. We have been trying to predict the risk of falling by conducting a balance test with platform translation stimuli to point out the influence of aging and the differences in individuals that it is difficult to determine by means of posturography. As a first step, in this study, we investigated the change of the displacement of the COP after forward platform translation in normal subjects. We also recorded EMG from the lower limbs simultaneously to investigate the muscles used to maintain normal erect posture.
2. Methods 2.1. Subjects About 26 (13 males and 13 females) normal young subjects (24.8±2.74 years, 166.5±9.25 cm height, 60.0±11.48 kg weight, means±1SD) and 20 (10 males and 10 females) normal elderly subjects (65.4±3.62 years, 159.4±7.80 cm height, 58.6±7.98 kg weight) with no history of neuromuscular disorders volunteered for this investigation. Each subject was fully informed about the possible risks and the nature of the experiment and each signed the informed consent. Neurologic examination was normal and none had a Romberg sign. 2.2. Experimental design Each subject stood barefoot on the three dimensional force plate on the platform (Fig. 1), with feet parallel and gazed at a target, a circle 20 mm in diameter for 30 s. First, all subjects were measured at rest standing with eyes open and with eyes closed. As to the forward platform translations, the time took 0.15 s, and the displacements were 3.75, 7.5, 10, 15, 20, and 30 mm for 0.15 s and recording were obtained over
30 s. The six trials were carried out at random, and the COP and EMG data were recorded during standing. 2.3. Apparatus and procedures For COP recording, the three dimensional force plate on the platform (GS-6900B, Anima, Japan) was located in a well-lighted room. The device consisted of two computers and a force plate, control box, and switch for giving platform translation (Fig. 1). The force plate was divided into two plates to calculate COP for each foot. One plate had three load cells that were located on an isosceles triangle. The data of COP were collected by the computer through an analog to a digital convertor at 50 Hz. For EMG recording, surface electrodes (NE-155A, Nihon Kohden Corporation, Japan) were secured to the skin over the belly of eight muscles (gluteus maximus, rectus femoris, biceps femoris, tibialis anterior, soleus, gastrocnemius, abductor hallucis, extensor digitorum brevis) of left leg by means of paste (Z-401CE, Nihon Kohden Corporation, Japan). The electrodes were discs, 11 mm in diameter, manufactured with Ag/AgCl. The EMG data were collected using a polygraph (DAE-2110, Nihon Kohden Corporation, Japan) at 1 kHz. 2.4. Data analysis In the analysis of static COP recordings, we compared the data that were collected from normal subjects provided by the company that produced the device [35] with the data from the subjects in this study. In dynamic trials, the COP data were analyzed from the data for 5 s after forward platform translations (Fig. 2). The results of the COP were analyzed for the first 5 s after forward platform translations, since previous studies in disorders of posture control, e.g. patients with Parkinson’s disease, showed most impressive changes at this time period (unpublished data). We used the following in the analysis of the COP data in dynamic trials: the displacement length of the COP for x-direction (lateral), the displacement length of the COP for y-direction (anterior–posterior), maximum amplitude for xdirection, maximum amplitude for y-direction. We selected the indexes for y-direction, since the effects of translation stimuli for displacement of the COP were induced most remarkably by means of paying attention to the ydirection, i.e. anterior–posterior direction, as it was parallel with the direction of stimuli. We also selected the indexes for x-direction, since we thought the results of displacement of the COP for x-direction might be shown to compensate for the motion in the y-direction with stimuli exceeding some of the levels. We judged that muscles that were more clearly activated, as observed by EMG recordings, during forward platform translations, than during quiet standings before
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Fig. 1.
397
The experimental design.
3. Results
Fig. 2. Schematic diagram to the relationship between recording and analysis periods.
translations, were ‘on’, and those that were not clearly activated by EMG signal were ‘off’; i.e. if (maximum amplitude of EMG during translation)/(maximum amplitude of EMG before translation) ⬎1.2 was ‘on’, else ‘off’ (Fig. 3). Significant differences between young and elderly groups were analyzed by the Mann–Whitney’s U-test for the results of the COP, and by Fisher’s exact probability test with raw EMG data.
Fig. 4 shows the mean values of displacement of the COP recorded for 5 s after forward platform translations in the young and elderly groups: (a) x-direction (lateral); (b) y-direction (anterior–posterior). For y-direction, the mean displacement of the COP for 5 s showed a moderate increase from 3.75 to 15 mm. Whereas with the stimuli between 20 and 30 mm, the results were similar to those of 15 mm. For the x-direction, the mean displacement of the COP showed little change. The elderly group showed significantly (p⬍0.05) larger sway than the young group. Fig. 5 shows the means of the maximum amplitude of the COP: (a) x-direction (lateral); (b) y-direction (anterior–posterior). In the small platform translations, there were no significant differences between young and elderly groups. Whereas, with larger stimuli, there were significant differences (p⬍0.05) of the COP displacement between young and elderly groups. Fig. 6 shows the number of muscles used during the corrective responses with the platform translations. In both young and elderly groups, the number of muscles activated increased with greater displacement of the platform for maintaining the standing posture. Comparing young and elderly groups, significant differences
398
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Fig. 3. Schematic diagram as to criterion for muscle activation; this figure shows typical sample of raw EMG waveform and translation trigger sent from switch. We judged muscles activation ‘on’, if maximum amplitude after translation was clearly larger than maximum amplitude before translation (i.e. during quiet standing). We defined ‘on’ with (maximum amplitude after translation)/(maximum amplitude before translation)⬎1.2.
appeared in accordance with increased displacement of the platform, especially in the range 10–30 mm. As to the individual muscles, there was no change with aging on tibialis anterior activation. Moreover we found that activation of the abductor hallucis and extensor digitorum brevis muscles in the elderly group was significantly increased (p⬍0.05) compared with the young group. For proximal muscles, Fig. 7 shows that the elderly group used more muscles than the young group during stimuli with greater translation displacement, i.e. for more than 15 mm in displacement of the platform. The displacement of the COP did not show a significant difference (p⬎0.05) between sexes in young subjects. However in the elderly subjects, the results of some of the trials showed that males were more unstable compared with females (Table 1). 4. Discussion
Fig. 4. The mean displacement of the COP for 5 s after forward translation in young and elderly groups: (a) x-direction (lateral); (b) y-direction (anterior–posterior).
The displacement of the COP has been measured as an assessment of postural control. In addition to the measurement of the COP during quiet standing, corrective responses were observed by measurement of the COP with translation and rotation [10–13]. Szturm et al. [16] investigated the COP and EMG with varying acceleration of platform translation and rotation. The results showed that the larger acceleration of platform caused the greater displacement of the COP and magnitude of EMG. Our data indicated that the displacement of the COP in platform translations from 3.75 to 15 mm showed a tendency to increase for y-direction (anterior– posterior). The EMG recordings revealed that the number of muscles used increased with the increase in displacement of the platform. Therefore the results were
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
399
Fig. 6. The mean number of muscles used for standing after forward translation in the young and elderly groups. x-axis shows displacement of the platform, y-axis shows the averages of the number of muscles activated in young and elderly groups, respectively.
Fig. 5. The mean maximum amplitude of the COP after forward translation in young and elderly: (a) x-direction (lateral); (b) y-direction (anterior–posterior).
influenced by the intensity of the stimuli, and it may be possible to assess the postural ability of individuals by means of this test. The results of the other stimuli between 20 and 30 mm varied greatly. In spite of greater intensity of the stimuli, the displacements of the COP did not show a tendency to rise compared to that of 15 mm. The differences between the effects of short displacement and longer displacements provided some insight into posture control. With short stimuli, the increase in activation of lower limb muscles such as tibialis anterior, soleus and gastrocnemius occurred according to the intensity of the stimuli. We think that these results indicate that ankle synergy stabilizes the erect body. In other words, it may be possible to estimate the individual’s ability to make corrective responses by ankle synergy from the study
of short platform translations. Furthermore, the results suggest the possibility of devising an index of the ability of posture control from the effect of the range of motion (ROM) for the ankle and aging by means of this type of testing. With greater stimuli, activation of the proximal muscles such as the gluteus maximus and biceps femoris increased. However the increase of displacement of the COP was not so remarkable. These results suggest that hip synergy and/or the ankle synergy stabilize the body in individuals. In these cases, therefore, we think that postural control was multi-segmental and performed by more muscles than in the above-mentioned cases, and the results were influenced by individual differences. Some of the factors that may produce the individual differences may be muscle volumes, muscle strength, ROM, nerve conductive velocity and others. In the displacement of the COP for x-direction, the differences between young and elderly groups were not significant with small stimuli, but were significant with large stimuli (p⬍0.05). These results suggest that the anterior–posterior oscillation which was the same as the direction of the platform translation was compensated by lateral-medial oscillation to prevent falling [36]. However lateral-medial oscillation was much smaller than anterior–posterior. This observation needs further investigation in the future. In previous studies [3], females showed less stability than males. In this study, however, the displacement of the COP did not show a significant difference between sexes in young subjects, although males were taller in height and heavier in weight than females. In the elderly subjects, the results of some of the trials showed males more unstable than females. Males had a higher average height than females, so the differences with regard to
400
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Fig. 7. The percentage of muscles used during standing after forward translations in each muscle: (a) gluteus maximus; (b) rectus femoris; (c) biceps femoris; (d) tibialis anterior; (e) soleus; (f) gastrocnemius; (g) abductor hallucis; (h) extensor digitorum brevis. x-axis shows the displacement of the platform, y-axis shows the percentage of activated muscles in young and elderly groups, respectively.
sex were not clear. The differences of height between males and females did not influence the displacement of the COP in young subjects, but did in some of the results in the elderly subjects. We think that the slight differences, e.g. the differences in height between males and
females, may have an effect on the results of COP in the elderly group. The elderly subjects in this study were 59–72 years old, and number of people more than 70 years old in them were three. They would be relatively young for
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Table 1 The effect of sex in the elderly on displacement of the center of the pressure after platform translation (n.p.=not significant) Male Mean Age Height Weight
66.3 165.6 63.9
The COP displacement Total 3.75 9.1 7.50 16.3 10.00 27.0 15.00 26.6 20.00 32.2 30.00 30.8 x-direction 3.75 2.8 7.50 4.2 10.00 6.5 15.00 6.9 20.00 8.3 30.00 9.6 y-direction 3.75 7.9 7.50 14.6 10.00 25.1 15.00 24.2 20.00 29.7 30.00 27.3
Female SD
Mean
Significance SD
3.40 5.02 6.71
64.4 153.3 53.2
3.75 4.40 5.13
n.p. p⬍0.01 p⬍0.01
4.77 9.74 15.22 14.23 19.00 12.07
6.4 10.9 11.5 24.3 20.2 23.9
1.88 4.32 2.60 10.51 7.40 3.57
n.p. n.p. p⬍0.01 n.p. n.p. n.p.
1.65 2.45 3.85 4.52 5.13 6.49
2.1 2.8 3.0 6.5 6.0 8.4
0.72 1.66 1.58 3.69 3.84 2.89
n.p. n.p. p⬍0.01 n.p. n.p. n.p.
4.85 9.83 14.05 12.95 17.86 9.54
5.6 10.0 10.4 22.2 18.0 20.7
1.74 3.98 2.16 9.90 6.31 3.34
n.p. n.p. p⬍0.01 n.p. n.p. n.p.
0.7 0.7 0.9 1.7 1.8 2.8
0.34 0.41 0.36 1.15 1.34 0.95
n.p. n.p. p⬍0.05 n.p. n.p. n.p.
1.6 3.1 3.6 7.7 6.7 7.5
0.63 1.35 0.95 3.88 2.73 1.76
n.p. n.p. p⬍0.01 n.p. n.p. p⬍0.05
Maximum amplitude of COP x-direction 3.75 0.9 0.85 7.50 1.3 1.10 10.00 1.7 0.99 15.00 1.9 1.31 20.00 2.3 1.33 30.00 2.8 2.19 y-direction 3.75 2.2 1.12 7.50 3.9 2.65 10.00 8.2 4.53 15.00 8.1 4.16 20.00 9.9 4.26 30.00 9.3 2.60
investigating postural control in the elderly. We will investigate about prediction of falls for the future. We therefore carried out the examination in this study in such subjects. In this study, we gave the subjects relatively small platform displacements. For example, Szturm et al. [16] used three large translation of platform that average speed was from 14.2 to 28.7 cm/s; Nardone et al. [20] used translations whose average speed was from 21 to 75 cm/s. They used such large translations in young people. We thought that safety was an important factor and that the tests should not impose a hardship on the subjects. As a result, the displacements of the COP in
401
the elderly were significantly greater than in the young. The results found were influenced by aging during small platform translations like static posturography [4]. In the elderly group, however, the deviations of the results were great in dynamic posturography compared with static posturography. We think that it may be easier to evaluate posture control in an individual with a dynamic test than with a static test in elderly people. Furthermore, we think that the results of dynamic tests are more useful in predicting falling in the elderly. In the experimental design of this study, accelerations of the platform translations were unknown, so it is necessary to investigate the motion of the force plate in the platform. We plan to install a potentiometer in this device to investigate the acceleration of the force plate with the platform translations. The polygraph used for EMG recording in our experimental design, may not record detailed motor unit potentials, but the recordings readily showed the muscles activated during platform translation and we were able to determine muscle activation by ‘on’ or ‘off’ of the EMG activity. However, great variations of responses were observed in the elderly group as reported in the past [3]. Inglis et al. [32] suggested that lower limb played an important role for postural control by investigating EMG in neuropathy patients. We plan to conduct further objective tests, like nerve conduction studies to investigate these variations. In conclusion, this study suggests that the individual’s ability to control posture can be assessed by measuring the displacement of the COP after platform translation, and that the effects of aging on equilibrium can be observed. This study also suggests that the number of muscles activated after platform translation during standing shows an effect of aging, and this may be helpful in understanding how synergies work. Furthermore the testing in this study is safe and without pain. We anticipate that this type of testing will be useful in the evaluation of postural control in the elderly.
Acknowledgements This work was supported financially in part by the Grant-in-Aid for Scientific Research (C) (60301917 [H.S.]) from Japan Society for the Promotion of Science. We would like to thank Prof. R. F. Mayer for reviewing the manuscript.
References [1] Basler A. Zur Physiology des Hockens. Z Biol 1929;88:523–30. [2] Collins JJ, De Luca CJ, Burrows A, Lipsitz LA. Age-related changes in open-loop and closed-loop postural control mechanisms. Exp Brain Res 1995;104(3):480–92. [3] Overstall PW, Johnson AL, Exton-Smith AN. Instability and falls in the elderly. Age Aging 1978;7(Suppl.):92–6.
402
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
[4] Panzer VP, Bandinelli S, Hallett M. Biomechanical assessment of quiet standing and changes associated with aging. Arch Phys Med Rehabil 1995;76(2):151–7. [5] Sheldon JH, Wolverhampton. The effect of age on the control of sway. Geront Clin 1963;5:129–38. [6] Tanaka T, Takeda H, Izumi T, Ino S, Ifukube T. Effects on the location of the centre of gravity and the foot pressure contribution to standing balance associated with ageing. Ergonomics 1999;42(7):997–1010. [7] Woollacott MH, Shumway-Cook A, Nashner LM. Aging and posture control: changes in sensory organization and muscular coordination. Int J Aging Hum Dev 1986;23(2):97–114. [8] Wolfson L, Judge J, Whipple R, King M. Strength is a major factor in balance, gait, and the occurrence of falls. J Gerontol Ser A, Biol Sci Med Sci 1995;50:64–7. [9] Allum JH, Honegger F, Schicks H. Vestibular and proprioceptive modulation of postural synergies in normal subjects. J Vestibular Res 1993;3(1):59–85. [10] Di Fabio RP, Emasithi A, Paul S. Validity of visual stabilization conditions used with computerized dynamic platform posturography. Acta Oto-Laryngol 1998;118(4):449–54. [11] Gollhofer A, Horstmann GA, Berger W, Dietz V. Compensation of translational and rotational perturbations in human posture: stabilization of the centre of gravity. Neurosci Lett 1989;105(12):73–8. [12] Hlavacka F, Shupert CL, Horak FB. The timing of galvanic vestibular stimulation affects responses to platform translation. Brain Res 1999;821(1):8–16. [13] Kapteyn TS et al. Standarization in platform stabilometry being apart of posturography. Agressology 1983;24:321–6. [14] Keshner EA, Woollacott MH, Debu B. Neck, trunk and limb muscle responses during postural perturbations in humans. Exp Brain Res 1988;71(3):455–66. [15] Shepard NT. The clinical use of dynamic posturography in the elderly. Ear Nose Throat J 1989;68:940–57. [16] Szturm T, Fallang B. Effects of varying acceleration of platform translation and toes-up rotations on the pattern and magnitude of balance reaction in humans. J Vestibular Res 1998;8(5):381–97. [17] Dietz V, Trippel M, Discher M, Horstmann GA. Compensation of human stance perturbations: selection of the appropriate electromyographic pattern. Neurosci Lett 1991;126(1):71–4. [18] Gilles M, Wing AM, Kirker SGB. Lateral balance organisation in human stance in response to a random or predictable perturbation. Exp Brain Res 1999;124:137–44. [19] Henry SM, Fung J, Horak FB. EMG responses to maintain stance during multidirectional surface translations. J Neurophysiol 1998;80(4):1939–50. [20] Nardone A, Giordano A, Corra T, Schieppati M. Responses of leg muscles in humans displaced while standing. Effects of types of perturbation and of postural set. Brain 1990;113(Pt 1):65–84. [21] Nashner LM, Woollacott M, Tuma G. Organization of rapid responses to postural and locomotor-like perturbations of standing man. Exp Brain Res 1979;36(3):463–76. [22] Nashner LM. Fixed patterns of rapid postural responses among leg muscles during stance. Exp Brain Res 1977;30:13–24. [23] Schieppati M, Nardone A, Siliotto R, Grasso M. Early and late stretch responses of human foot muscles induced by perturbation of stance. Exp Brain Res 1995;105(3):411–22. [24] Wolf SL, Ammerman J, Jann B. Organization of responses in human lateral gastrocnemius muscle to specified body perturbations. J Electromyography Kinesiol 1998;8:11–21. [25] Inglis JT, Macpherson JM. Bilateral labyrinthectomy in the cat: effects on the postural response to translation. J Neurophysiol 1995;73(3):1181–91. [26] Jacobs R, Macpherson JM. Two functional muscle groupings during postural equilibrium tasks in standing cats. J Neurophysiol 1996;76(4):2402–11.
[27] Macpherson JM, Horak FB, Dunbar DC, Dow RS. Stance dependence of automatic postural adjustments in humans. Exp Brain Res 1989;78(3):557–66. [28] Rushmer DS, Russell CJ, Macpherson J, Phillips JO, Dunbar DC. Automatic postural responses in the cat: responses to headward and tailward translation. Exp Brain Res 1983;50(1):45–61. [29] Allum JH, Honegger F, Schicks H. The influence of a bilateral peripheral vestibular deficit on postural synergies. J Vestibular Res 1994;4(1):49–70. [30] Allum JH, Honegger F. Synergies and strategies underlying normal and vestibulary deficient control of balance: implication for neuroprosthetic control. Prog Brain Res 1993;97:331–48. [31] Horak FB, Diener HC. Cerebellar control of postural scaling and central set in stance. J Neurophysiol 1994;72(2):479–93. [32] Inglis JT, Horak FB, Shupert CL, Jones-Rycewicz C. The importance of somatosensory information in triggering and scaling automatic postural responses in human. Exp Brain Res 1994;101:159–64. [33] Schieppati M, Nardone A. Free and supported stance in Parkinson’s disease. The effect of posture and ‘postural set’ on leg muscle responses to perturbation, and its relation to the severity of the disease. Brain 1991;114(Pt 3):1227–44. [34] Shumway-Cook A, Woollacott M, Kerns KA, Baldwin M. The effects of two types of cognitive tasks on postural stability in older adults with and without a history of falls. J Gerontol Ser A, Biol Sci Med Sci 1997;52(4):M232–40. [35] Imaoka K, Murase H, Fukuhara M. Collection of data for healthy subjects in stabilometry. Equilibrium Res Suppl 1997;12:1–84 (Japanese). [36] Rietdyk S, Patla AE, Winter DA, Ishac MG, Little CE. NACOB presentation CSB New Investigator Award. Balance recovery from medio-lateral perturbations of the upper body during standing. North American Congress on Biomechanics. J Biomech 1999;32(11):1149–58.
Hitomi Nakamura received the B.S. degree in computer science and system engineering in 1995 from Muroran Institute of Technology, Muroran, Japan. She also received the M.S. degree in bioengineering, and the Ph.D. degree in rehabilitation medicine from Hokkaido University, Sapporo, Japan, in 1997 and 2001, respectively. She is a Post Doctoral Fellow in Satellite Venture Business Laboratory at Muroran Institute of Technology. Her research interests are in the area of bioengineering, computer science and rehabilitation engineering including human being measurement and virtual reality technique.
Takamasa Tsuchida received the PhD degree in medicine from Chiba University, Graduate School of Medicine, Japan, in 1998. He passed the Japanese Speciality Board Examination for Orthopaedics in 1993 and Rehabilitation Medicine in 1998. He is an instructor of Rehabilitation Medicine, Hokkaido University, Graduate School of Medicine. His research interests focus on gait analysis and rehabilitation medicine in general.
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403 Yukio Mano, M.D graduated from Nagoya University School of Medicine in 1968. He completed residency training for Physical Medicine and Rehabilitation at New York University in 1974, and was trained for Neurology at Baylor College of Medicine in 1975, and University of Maryland in 1976. He received the Ph.D degree from Nagoya University in 1978. He was a chief researcher in National Center for Mental, Nervous and Muscular Disorders in 1978-1981, and was Associate Professor in Neurology in Nara Medical College in 1981-1995. He is Professor and Chairman of Department of Rehabilitation Medicine, Hokkaido University Postgraduate School of Medicine. He is a board member of the International Society of Electrophysiology and Kinesiology (ISEK), and is a chairman of council board of the Japanese Society of Electrophysiology and Kinesiology (JSEK). He is also one of the council members of Japanese Society of Biomechanics, and Japanese Association of Rehabilitation Medicine.
403
The assessment of posture control in the elderly using the displacement of the center of pressure after forward platform translation H. Nakamura , T. Tsuchida , Y. Mano
*
Department of Rehabilitation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido, Japan Received 27 July 2000; received in revised form 23 February 2001; accepted 22 April 2001
Abstract We investigated the change of the center of pressure (COP) after forward platform translations in healthy subjects. These studies were performed on 26 normal young subjects and 20 healthy elderly subjects, who had a normal neurologic examination. Subjects stood barefoot on a three dimensional force plate on the platform, with feet parallel. The duration of the forward platform translations was 0.15 s, and the displacements were 3.75, 7.5, 10, 15, 20, and 30 mm. Six trials were carried out at random. The COP data were recorded for 35 s during standing, and were analyzed for 5 s after translation. With the platform translation displacements from 3.75 to 15 mm, displacement of the COP showed a tendency to increase in all subjects. Whereas with the stimuli between 20 and 30 mm, the results were more varied. The elderly group showed significantly (p⬍0.05) larger sway than the young group. These results indicate that the individual ability of posture control may be assessed by means of measuring the sway of the center of gravity after platform translation. Electromyography was carried out simultaneously, it showed that elderly people contrary to young subjects used proximal biceps femoris and distal foot muscles at an early stage of the platform translation (p⬍0.05), suggesting lack of ankle stability with aging. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Posture control; Platform translation; Center of pressure
1. Introduction Displacement of the center of pressure (COP) on a platform has been measured and used as an index of postural stability in standing. In 1929, it was first reported by Basler [1] who measured displacement of the COP. In following studies, the effects of age, sex, and other factors were determined [2–7]. As posturography is one of the tests of equilibrium, the displacement of the COP increased as an effect of aging. Also the relationship between the displacement of the COP and the strength of muscles was reported in Ref. [8]. With regard to the difference due to sex, the results of studies showed that the displacement of the COP for females was more unstable than males [3]. Moreover, in subsequent studies, corrective responses were observed by
* Corresponding author. Tel.: +81-11-706-6066; fax: +81-11-7066067. E-mail address: [email protected] (Y. Mano).
measurement of the COP with backward and forward platform translations and rotations [9–16]. Furthermore, there were many studies that measured electromyography (EMG) simultaneously in the lower limbs [17–24]. In experiments with cats [25–28], activation of thigh and foot muscles were observed as corrective responses to forward and backward translations, and the corrective responses for translations were investigated in quadrupedal stance and standing. Besides being reported in normal subjects, measurements of the COP were carried out in a variety of patients such as: bilateral peripheral vestibular deficits, diabetic peripheral neuropathy, Parkinson’s disease, and others [29–33]. Displacements of the COP were also measured to analyze the relationship between the stability of posture and falling. It is important to predict or prevent falling in the elderly. The elderly suffer injuries and their bones may fracture in a fall, and it often takes a long time for a complete recovery. What makes it even worse is that the injuries by falls prevent an active social life for the elderly, and this results in greater decline of body functions. There-
1050-6411/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 0 5 0 - 6 4 1 1 ( 0 1 ) 0 0 0 1 6 - 5
396
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
after the elderly may fall again. However it is difficult to exclude the effects of aging on the value of displacement of the COP in the existing quiet-standing test. Shumway-Cook and colleagues [34] investigated the effects of two different types of cognitive tasks on stability, as measured by COP displacement, in young versus older adults with and without a history of falls. Two cognitive tasks, a sentence completion and a visual perceptual matching task, were used to produce changes in attention during quiet stance under flat versus compliant surface conditions. While no differences were found between the young adults and the older healthy adults on a firm surface without a task, when the task complexity was increased, significant differences in postural stability between the two groups became apparent. In contrast to the young and healthy older adults, postural stability in older adults with a history of falls was significantly affected by both cognitive tasks. We have been trying to predict the risk of falling by conducting a balance test with platform translation stimuli to point out the influence of aging and the differences in individuals that it is difficult to determine by means of posturography. As a first step, in this study, we investigated the change of the displacement of the COP after forward platform translation in normal subjects. We also recorded EMG from the lower limbs simultaneously to investigate the muscles used to maintain normal erect posture.
2. Methods 2.1. Subjects About 26 (13 males and 13 females) normal young subjects (24.8±2.74 years, 166.5±9.25 cm height, 60.0±11.48 kg weight, means±1SD) and 20 (10 males and 10 females) normal elderly subjects (65.4±3.62 years, 159.4±7.80 cm height, 58.6±7.98 kg weight) with no history of neuromuscular disorders volunteered for this investigation. Each subject was fully informed about the possible risks and the nature of the experiment and each signed the informed consent. Neurologic examination was normal and none had a Romberg sign. 2.2. Experimental design Each subject stood barefoot on the three dimensional force plate on the platform (Fig. 1), with feet parallel and gazed at a target, a circle 20 mm in diameter for 30 s. First, all subjects were measured at rest standing with eyes open and with eyes closed. As to the forward platform translations, the time took 0.15 s, and the displacements were 3.75, 7.5, 10, 15, 20, and 30 mm for 0.15 s and recording were obtained over
30 s. The six trials were carried out at random, and the COP and EMG data were recorded during standing. 2.3. Apparatus and procedures For COP recording, the three dimensional force plate on the platform (GS-6900B, Anima, Japan) was located in a well-lighted room. The device consisted of two computers and a force plate, control box, and switch for giving platform translation (Fig. 1). The force plate was divided into two plates to calculate COP for each foot. One plate had three load cells that were located on an isosceles triangle. The data of COP were collected by the computer through an analog to a digital convertor at 50 Hz. For EMG recording, surface electrodes (NE-155A, Nihon Kohden Corporation, Japan) were secured to the skin over the belly of eight muscles (gluteus maximus, rectus femoris, biceps femoris, tibialis anterior, soleus, gastrocnemius, abductor hallucis, extensor digitorum brevis) of left leg by means of paste (Z-401CE, Nihon Kohden Corporation, Japan). The electrodes were discs, 11 mm in diameter, manufactured with Ag/AgCl. The EMG data were collected using a polygraph (DAE-2110, Nihon Kohden Corporation, Japan) at 1 kHz. 2.4. Data analysis In the analysis of static COP recordings, we compared the data that were collected from normal subjects provided by the company that produced the device [35] with the data from the subjects in this study. In dynamic trials, the COP data were analyzed from the data for 5 s after forward platform translations (Fig. 2). The results of the COP were analyzed for the first 5 s after forward platform translations, since previous studies in disorders of posture control, e.g. patients with Parkinson’s disease, showed most impressive changes at this time period (unpublished data). We used the following in the analysis of the COP data in dynamic trials: the displacement length of the COP for x-direction (lateral), the displacement length of the COP for y-direction (anterior–posterior), maximum amplitude for xdirection, maximum amplitude for y-direction. We selected the indexes for y-direction, since the effects of translation stimuli for displacement of the COP were induced most remarkably by means of paying attention to the ydirection, i.e. anterior–posterior direction, as it was parallel with the direction of stimuli. We also selected the indexes for x-direction, since we thought the results of displacement of the COP for x-direction might be shown to compensate for the motion in the y-direction with stimuli exceeding some of the levels. We judged that muscles that were more clearly activated, as observed by EMG recordings, during forward platform translations, than during quiet standings before
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Fig. 1.
397
The experimental design.
3. Results
Fig. 2. Schematic diagram to the relationship between recording and analysis periods.
translations, were ‘on’, and those that were not clearly activated by EMG signal were ‘off’; i.e. if (maximum amplitude of EMG during translation)/(maximum amplitude of EMG before translation) ⬎1.2 was ‘on’, else ‘off’ (Fig. 3). Significant differences between young and elderly groups were analyzed by the Mann–Whitney’s U-test for the results of the COP, and by Fisher’s exact probability test with raw EMG data.
Fig. 4 shows the mean values of displacement of the COP recorded for 5 s after forward platform translations in the young and elderly groups: (a) x-direction (lateral); (b) y-direction (anterior–posterior). For y-direction, the mean displacement of the COP for 5 s showed a moderate increase from 3.75 to 15 mm. Whereas with the stimuli between 20 and 30 mm, the results were similar to those of 15 mm. For the x-direction, the mean displacement of the COP showed little change. The elderly group showed significantly (p⬍0.05) larger sway than the young group. Fig. 5 shows the means of the maximum amplitude of the COP: (a) x-direction (lateral); (b) y-direction (anterior–posterior). In the small platform translations, there were no significant differences between young and elderly groups. Whereas, with larger stimuli, there were significant differences (p⬍0.05) of the COP displacement between young and elderly groups. Fig. 6 shows the number of muscles used during the corrective responses with the platform translations. In both young and elderly groups, the number of muscles activated increased with greater displacement of the platform for maintaining the standing posture. Comparing young and elderly groups, significant differences
398
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Fig. 3. Schematic diagram as to criterion for muscle activation; this figure shows typical sample of raw EMG waveform and translation trigger sent from switch. We judged muscles activation ‘on’, if maximum amplitude after translation was clearly larger than maximum amplitude before translation (i.e. during quiet standing). We defined ‘on’ with (maximum amplitude after translation)/(maximum amplitude before translation)⬎1.2.
appeared in accordance with increased displacement of the platform, especially in the range 10–30 mm. As to the individual muscles, there was no change with aging on tibialis anterior activation. Moreover we found that activation of the abductor hallucis and extensor digitorum brevis muscles in the elderly group was significantly increased (p⬍0.05) compared with the young group. For proximal muscles, Fig. 7 shows that the elderly group used more muscles than the young group during stimuli with greater translation displacement, i.e. for more than 15 mm in displacement of the platform. The displacement of the COP did not show a significant difference (p⬎0.05) between sexes in young subjects. However in the elderly subjects, the results of some of the trials showed that males were more unstable compared with females (Table 1). 4. Discussion
Fig. 4. The mean displacement of the COP for 5 s after forward translation in young and elderly groups: (a) x-direction (lateral); (b) y-direction (anterior–posterior).
The displacement of the COP has been measured as an assessment of postural control. In addition to the measurement of the COP during quiet standing, corrective responses were observed by measurement of the COP with translation and rotation [10–13]. Szturm et al. [16] investigated the COP and EMG with varying acceleration of platform translation and rotation. The results showed that the larger acceleration of platform caused the greater displacement of the COP and magnitude of EMG. Our data indicated that the displacement of the COP in platform translations from 3.75 to 15 mm showed a tendency to increase for y-direction (anterior– posterior). The EMG recordings revealed that the number of muscles used increased with the increase in displacement of the platform. Therefore the results were
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
399
Fig. 6. The mean number of muscles used for standing after forward translation in the young and elderly groups. x-axis shows displacement of the platform, y-axis shows the averages of the number of muscles activated in young and elderly groups, respectively.
Fig. 5. The mean maximum amplitude of the COP after forward translation in young and elderly: (a) x-direction (lateral); (b) y-direction (anterior–posterior).
influenced by the intensity of the stimuli, and it may be possible to assess the postural ability of individuals by means of this test. The results of the other stimuli between 20 and 30 mm varied greatly. In spite of greater intensity of the stimuli, the displacements of the COP did not show a tendency to rise compared to that of 15 mm. The differences between the effects of short displacement and longer displacements provided some insight into posture control. With short stimuli, the increase in activation of lower limb muscles such as tibialis anterior, soleus and gastrocnemius occurred according to the intensity of the stimuli. We think that these results indicate that ankle synergy stabilizes the erect body. In other words, it may be possible to estimate the individual’s ability to make corrective responses by ankle synergy from the study
of short platform translations. Furthermore, the results suggest the possibility of devising an index of the ability of posture control from the effect of the range of motion (ROM) for the ankle and aging by means of this type of testing. With greater stimuli, activation of the proximal muscles such as the gluteus maximus and biceps femoris increased. However the increase of displacement of the COP was not so remarkable. These results suggest that hip synergy and/or the ankle synergy stabilize the body in individuals. In these cases, therefore, we think that postural control was multi-segmental and performed by more muscles than in the above-mentioned cases, and the results were influenced by individual differences. Some of the factors that may produce the individual differences may be muscle volumes, muscle strength, ROM, nerve conductive velocity and others. In the displacement of the COP for x-direction, the differences between young and elderly groups were not significant with small stimuli, but were significant with large stimuli (p⬍0.05). These results suggest that the anterior–posterior oscillation which was the same as the direction of the platform translation was compensated by lateral-medial oscillation to prevent falling [36]. However lateral-medial oscillation was much smaller than anterior–posterior. This observation needs further investigation in the future. In previous studies [3], females showed less stability than males. In this study, however, the displacement of the COP did not show a significant difference between sexes in young subjects, although males were taller in height and heavier in weight than females. In the elderly subjects, the results of some of the trials showed males more unstable than females. Males had a higher average height than females, so the differences with regard to
400
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Fig. 7. The percentage of muscles used during standing after forward translations in each muscle: (a) gluteus maximus; (b) rectus femoris; (c) biceps femoris; (d) tibialis anterior; (e) soleus; (f) gastrocnemius; (g) abductor hallucis; (h) extensor digitorum brevis. x-axis shows the displacement of the platform, y-axis shows the percentage of activated muscles in young and elderly groups, respectively.
sex were not clear. The differences of height between males and females did not influence the displacement of the COP in young subjects, but did in some of the results in the elderly subjects. We think that the slight differences, e.g. the differences in height between males and
females, may have an effect on the results of COP in the elderly group. The elderly subjects in this study were 59–72 years old, and number of people more than 70 years old in them were three. They would be relatively young for
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
Table 1 The effect of sex in the elderly on displacement of the center of the pressure after platform translation (n.p.=not significant) Male Mean Age Height Weight
66.3 165.6 63.9
The COP displacement Total 3.75 9.1 7.50 16.3 10.00 27.0 15.00 26.6 20.00 32.2 30.00 30.8 x-direction 3.75 2.8 7.50 4.2 10.00 6.5 15.00 6.9 20.00 8.3 30.00 9.6 y-direction 3.75 7.9 7.50 14.6 10.00 25.1 15.00 24.2 20.00 29.7 30.00 27.3
Female SD
Mean
Significance SD
3.40 5.02 6.71
64.4 153.3 53.2
3.75 4.40 5.13
n.p. p⬍0.01 p⬍0.01
4.77 9.74 15.22 14.23 19.00 12.07
6.4 10.9 11.5 24.3 20.2 23.9
1.88 4.32 2.60 10.51 7.40 3.57
n.p. n.p. p⬍0.01 n.p. n.p. n.p.
1.65 2.45 3.85 4.52 5.13 6.49
2.1 2.8 3.0 6.5 6.0 8.4
0.72 1.66 1.58 3.69 3.84 2.89
n.p. n.p. p⬍0.01 n.p. n.p. n.p.
4.85 9.83 14.05 12.95 17.86 9.54
5.6 10.0 10.4 22.2 18.0 20.7
1.74 3.98 2.16 9.90 6.31 3.34
n.p. n.p. p⬍0.01 n.p. n.p. n.p.
0.7 0.7 0.9 1.7 1.8 2.8
0.34 0.41 0.36 1.15 1.34 0.95
n.p. n.p. p⬍0.05 n.p. n.p. n.p.
1.6 3.1 3.6 7.7 6.7 7.5
0.63 1.35 0.95 3.88 2.73 1.76
n.p. n.p. p⬍0.01 n.p. n.p. p⬍0.05
Maximum amplitude of COP x-direction 3.75 0.9 0.85 7.50 1.3 1.10 10.00 1.7 0.99 15.00 1.9 1.31 20.00 2.3 1.33 30.00 2.8 2.19 y-direction 3.75 2.2 1.12 7.50 3.9 2.65 10.00 8.2 4.53 15.00 8.1 4.16 20.00 9.9 4.26 30.00 9.3 2.60
investigating postural control in the elderly. We will investigate about prediction of falls for the future. We therefore carried out the examination in this study in such subjects. In this study, we gave the subjects relatively small platform displacements. For example, Szturm et al. [16] used three large translation of platform that average speed was from 14.2 to 28.7 cm/s; Nardone et al. [20] used translations whose average speed was from 21 to 75 cm/s. They used such large translations in young people. We thought that safety was an important factor and that the tests should not impose a hardship on the subjects. As a result, the displacements of the COP in
401
the elderly were significantly greater than in the young. The results found were influenced by aging during small platform translations like static posturography [4]. In the elderly group, however, the deviations of the results were great in dynamic posturography compared with static posturography. We think that it may be easier to evaluate posture control in an individual with a dynamic test than with a static test in elderly people. Furthermore, we think that the results of dynamic tests are more useful in predicting falling in the elderly. In the experimental design of this study, accelerations of the platform translations were unknown, so it is necessary to investigate the motion of the force plate in the platform. We plan to install a potentiometer in this device to investigate the acceleration of the force plate with the platform translations. The polygraph used for EMG recording in our experimental design, may not record detailed motor unit potentials, but the recordings readily showed the muscles activated during platform translation and we were able to determine muscle activation by ‘on’ or ‘off’ of the EMG activity. However, great variations of responses were observed in the elderly group as reported in the past [3]. Inglis et al. [32] suggested that lower limb played an important role for postural control by investigating EMG in neuropathy patients. We plan to conduct further objective tests, like nerve conduction studies to investigate these variations. In conclusion, this study suggests that the individual’s ability to control posture can be assessed by measuring the displacement of the COP after platform translation, and that the effects of aging on equilibrium can be observed. This study also suggests that the number of muscles activated after platform translation during standing shows an effect of aging, and this may be helpful in understanding how synergies work. Furthermore the testing in this study is safe and without pain. We anticipate that this type of testing will be useful in the evaluation of postural control in the elderly.
Acknowledgements This work was supported financially in part by the Grant-in-Aid for Scientific Research (C) (60301917 [H.S.]) from Japan Society for the Promotion of Science. We would like to thank Prof. R. F. Mayer for reviewing the manuscript.
References [1] Basler A. Zur Physiology des Hockens. Z Biol 1929;88:523–30. [2] Collins JJ, De Luca CJ, Burrows A, Lipsitz LA. Age-related changes in open-loop and closed-loop postural control mechanisms. Exp Brain Res 1995;104(3):480–92. [3] Overstall PW, Johnson AL, Exton-Smith AN. Instability and falls in the elderly. Age Aging 1978;7(Suppl.):92–6.
402
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403
[4] Panzer VP, Bandinelli S, Hallett M. Biomechanical assessment of quiet standing and changes associated with aging. Arch Phys Med Rehabil 1995;76(2):151–7. [5] Sheldon JH, Wolverhampton. The effect of age on the control of sway. Geront Clin 1963;5:129–38. [6] Tanaka T, Takeda H, Izumi T, Ino S, Ifukube T. Effects on the location of the centre of gravity and the foot pressure contribution to standing balance associated with ageing. Ergonomics 1999;42(7):997–1010. [7] Woollacott MH, Shumway-Cook A, Nashner LM. Aging and posture control: changes in sensory organization and muscular coordination. Int J Aging Hum Dev 1986;23(2):97–114. [8] Wolfson L, Judge J, Whipple R, King M. Strength is a major factor in balance, gait, and the occurrence of falls. J Gerontol Ser A, Biol Sci Med Sci 1995;50:64–7. [9] Allum JH, Honegger F, Schicks H. Vestibular and proprioceptive modulation of postural synergies in normal subjects. J Vestibular Res 1993;3(1):59–85. [10] Di Fabio RP, Emasithi A, Paul S. Validity of visual stabilization conditions used with computerized dynamic platform posturography. Acta Oto-Laryngol 1998;118(4):449–54. [11] Gollhofer A, Horstmann GA, Berger W, Dietz V. Compensation of translational and rotational perturbations in human posture: stabilization of the centre of gravity. Neurosci Lett 1989;105(12):73–8. [12] Hlavacka F, Shupert CL, Horak FB. The timing of galvanic vestibular stimulation affects responses to platform translation. Brain Res 1999;821(1):8–16. [13] Kapteyn TS et al. Standarization in platform stabilometry being apart of posturography. Agressology 1983;24:321–6. [14] Keshner EA, Woollacott MH, Debu B. Neck, trunk and limb muscle responses during postural perturbations in humans. Exp Brain Res 1988;71(3):455–66. [15] Shepard NT. The clinical use of dynamic posturography in the elderly. Ear Nose Throat J 1989;68:940–57. [16] Szturm T, Fallang B. Effects of varying acceleration of platform translation and toes-up rotations on the pattern and magnitude of balance reaction in humans. J Vestibular Res 1998;8(5):381–97. [17] Dietz V, Trippel M, Discher M, Horstmann GA. Compensation of human stance perturbations: selection of the appropriate electromyographic pattern. Neurosci Lett 1991;126(1):71–4. [18] Gilles M, Wing AM, Kirker SGB. Lateral balance organisation in human stance in response to a random or predictable perturbation. Exp Brain Res 1999;124:137–44. [19] Henry SM, Fung J, Horak FB. EMG responses to maintain stance during multidirectional surface translations. J Neurophysiol 1998;80(4):1939–50. [20] Nardone A, Giordano A, Corra T, Schieppati M. Responses of leg muscles in humans displaced while standing. Effects of types of perturbation and of postural set. Brain 1990;113(Pt 1):65–84. [21] Nashner LM, Woollacott M, Tuma G. Organization of rapid responses to postural and locomotor-like perturbations of standing man. Exp Brain Res 1979;36(3):463–76. [22] Nashner LM. Fixed patterns of rapid postural responses among leg muscles during stance. Exp Brain Res 1977;30:13–24. [23] Schieppati M, Nardone A, Siliotto R, Grasso M. Early and late stretch responses of human foot muscles induced by perturbation of stance. Exp Brain Res 1995;105(3):411–22. [24] Wolf SL, Ammerman J, Jann B. Organization of responses in human lateral gastrocnemius muscle to specified body perturbations. J Electromyography Kinesiol 1998;8:11–21. [25] Inglis JT, Macpherson JM. Bilateral labyrinthectomy in the cat: effects on the postural response to translation. J Neurophysiol 1995;73(3):1181–91. [26] Jacobs R, Macpherson JM. Two functional muscle groupings during postural equilibrium tasks in standing cats. J Neurophysiol 1996;76(4):2402–11.
[27] Macpherson JM, Horak FB, Dunbar DC, Dow RS. Stance dependence of automatic postural adjustments in humans. Exp Brain Res 1989;78(3):557–66. [28] Rushmer DS, Russell CJ, Macpherson J, Phillips JO, Dunbar DC. Automatic postural responses in the cat: responses to headward and tailward translation. Exp Brain Res 1983;50(1):45–61. [29] Allum JH, Honegger F, Schicks H. The influence of a bilateral peripheral vestibular deficit on postural synergies. J Vestibular Res 1994;4(1):49–70. [30] Allum JH, Honegger F. Synergies and strategies underlying normal and vestibulary deficient control of balance: implication for neuroprosthetic control. Prog Brain Res 1993;97:331–48. [31] Horak FB, Diener HC. Cerebellar control of postural scaling and central set in stance. J Neurophysiol 1994;72(2):479–93. [32] Inglis JT, Horak FB, Shupert CL, Jones-Rycewicz C. The importance of somatosensory information in triggering and scaling automatic postural responses in human. Exp Brain Res 1994;101:159–64. [33] Schieppati M, Nardone A. Free and supported stance in Parkinson’s disease. The effect of posture and ‘postural set’ on leg muscle responses to perturbation, and its relation to the severity of the disease. Brain 1991;114(Pt 3):1227–44. [34] Shumway-Cook A, Woollacott M, Kerns KA, Baldwin M. The effects of two types of cognitive tasks on postural stability in older adults with and without a history of falls. J Gerontol Ser A, Biol Sci Med Sci 1997;52(4):M232–40. [35] Imaoka K, Murase H, Fukuhara M. Collection of data for healthy subjects in stabilometry. Equilibrium Res Suppl 1997;12:1–84 (Japanese). [36] Rietdyk S, Patla AE, Winter DA, Ishac MG, Little CE. NACOB presentation CSB New Investigator Award. Balance recovery from medio-lateral perturbations of the upper body during standing. North American Congress on Biomechanics. J Biomech 1999;32(11):1149–58.
Hitomi Nakamura received the B.S. degree in computer science and system engineering in 1995 from Muroran Institute of Technology, Muroran, Japan. She also received the M.S. degree in bioengineering, and the Ph.D. degree in rehabilitation medicine from Hokkaido University, Sapporo, Japan, in 1997 and 2001, respectively. She is a Post Doctoral Fellow in Satellite Venture Business Laboratory at Muroran Institute of Technology. Her research interests are in the area of bioengineering, computer science and rehabilitation engineering including human being measurement and virtual reality technique.
Takamasa Tsuchida received the PhD degree in medicine from Chiba University, Graduate School of Medicine, Japan, in 1998. He passed the Japanese Speciality Board Examination for Orthopaedics in 1993 and Rehabilitation Medicine in 1998. He is an instructor of Rehabilitation Medicine, Hokkaido University, Graduate School of Medicine. His research interests focus on gait analysis and rehabilitation medicine in general.
H. Nakamura et al. / Journal of Electromyography and Kinesiology 11 (2001) 395–403 Yukio Mano, M.D graduated from Nagoya University School of Medicine in 1968. He completed residency training for Physical Medicine and Rehabilitation at New York University in 1974, and was trained for Neurology at Baylor College of Medicine in 1975, and University of Maryland in 1976. He received the Ph.D degree from Nagoya University in 1978. He was a chief researcher in National Center for Mental, Nervous and Muscular Disorders in 1978-1981, and was Associate Professor in Neurology in Nara Medical College in 1981-1995. He is Professor and Chairman of Department of Rehabilitation Medicine, Hokkaido University Postgraduate School of Medicine. He is a board member of the International Society of Electrophysiology and Kinesiology (ISEK), and is a chairman of council board of the Japanese Society of Electrophysiology and Kinesiology (JSEK). He is also one of the council members of Japanese Society of Biomechanics, and Japanese Association of Rehabilitation Medicine.
403