{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

balance across lifespan

balance across lifespan - 1 without attention arson et...

Info iconThis preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 6
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 8
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 10
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 12
Background image of page 13
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 without attention arson, et al. {1998}. ac. Neuropsychola :hological findings. ibsessions, compul- New York: Wiley. 3 vocal cord in the . Movement Disor- , 3c Wiesendanger, 'rilles de la Tourette leptic treatment of (2000). Movement Ieractivity disorder. ntington disease in Development, 16, )take sited in post- ewology, 30, 558m 'ders of the central 1e neuropsychiatric 791. :rlmutter, 8., et al. :h streptococcal in )f Psychiatry, 155, , DOW, S. P., et ai. natric disorders as :natic fever. Ameri— M. M., Roth, S. J., area of the United :6 News, 3, 4543. )lved for those af 3. leuropsychological ?, 65—74. CHAPTER 10 Balance and Postural Eontrol across the lifespan HARRIET G. WILMAMS LAURA HO The ability to regulate and maintain balance is often taken for granted; however, it provides the primary foundation for mobility, for use of the upper extremities, and for ' maintaining overall functional independence throughout life. The development of bal- ' ' ance/postural control is a significant part of early development and changes in the ca- ' pacity to maintain balance are a critical factor associated with aging and loss of func~ tional ability. Children With poor baiance/postural control often have difficulty with acquisition of both gross and fine motor skills and frequently shovv deficits in a variety of visuomotor or eye—hand coordination behaviors. Balance functions are also of con- '. cern to the aging individual; nearly one-third or more of elderly individuals 65+ fall ' each year. Frail elderly fall even more frequently and suffer seriOus injuries and hospi- ' '3 talizations as a result. For all ages, lack of appropriate control of balance and posture f'can have negative effects on both mental and physical health; these effects are mani- fested in a variety of ways and include loss of confidence in ability to perform physical ' tasks, loss of independence, Withdrawal from social activities, and diminished self- image and self-esteem. The health care costs of falls and loss of independence for the elderly alone are estimated to reach some $132 billion by 2030. Add to this the in creasineg greater health care costs of providing services to young children with a vari- ety of developmental needs, and it is clear that it is important to understand the nature of balance/postural control, how it develops and declines, and What factors contribute ' to the development and maintenance of effective control of balance. WHAY ES BALANCE? ' Balance can be defined simply as the ability to maintain the center of gravity over the __ base of support (e.g., Nashner, 1997). The center of gravity in humans is located in the ' pelvic region; the exact location of the center of gravity at any given point in time is dependent on the position of the body (head, arms, legs, etc). The base of Support de~ 211 212 CLINICAL DlSORDERS fines the limits of stability and the limits of stability define the area within which the center of gravity must be maintained to avoid disequilibrium, instability, or a fall (gen- erally this is 121/2 degrees in anterior—posterior and 16 degrees in medial—lateral direc— tions). Balance is also frequently categorized as static or dynamic; static balance refers to the ability to maintain the center of gravity over the base of support during quiet standing or sitting (Woollacott 8c Tang, 1997). Dynamic balance is known as “mov- ing balance” and involves maintaining balance when the center of gravity and base of support are moving (as in reaching up for an object) or when the center of gravity is moving outside the base of support (as in walking up a flight of steps). The processes involved in maintaining balance are anticipatory, reactive, or a combination of the two (e.g., Cordo 8C Nashner, 1982; Haas, Diener, Rapp 36 Dichgans, 1989; lnglin & Woollacott, 1988; Nashner, 1977). Reactive control of balance occurs when perturba- tions or events that contribute to instability (e.g., a slip, push, or trip) are unexpected; anticipatory control of balance occurs when instability is expected or can be predicted and thereby is planned for (e.g., getting into or out of a car and waiking down a flight of stairs). Optimal balance functioning requires both effective reactive and anticipa- tory control applied appropriately to the demands made on the individual as he or she is attempting to maintain stationary balance or stay in control while moving. THE BALANQE/POSTURAL CONTROL SYSTEM The current view of balance control is based on systems models (e.g., Shumway-Cook 85 Woollacott, 2001; Wooliacott 85 ShnmwaymCook, 1990). This perspective of bal- ance describes the body as a mechanicai system with mass, which is subject to external (e.g., gravity and inertia) and internal forces (e.g., muscular contraction). Balance is also a multidimensional process, which involves the interaction and function of a num— ber of physiological systems; these inciude among others, the peripheral nervous sys— tem (PNS) and central nervous system (CNS), the muscular system (e.g., strength and muscular endurance), the skeletal system (joint range of motion, flexibility, bone strength, etc), and the visual, proprioceptive, and vestibular systems (e.g., Yim-Chiplis SC Talbot, 2000). The CNS is integral to maintenance of balance and postural control through its systematic monitoring and integration of information from the three major sensory systems and through organizing the appropriate motor output to activate the correc- tive responses needed to maintain balance. The former is referred to as sensory organia zation of posture/balance, the latter as the motor coordination component of posture/ balance. Input from the three primary sensory systems involved in balance/postural control normally previde redundant information about the state of equilibrium of the body and indicate whether or not a corrective response is needed and what the nature of that response should be. The relative importance of different sources of sensory infor- mation to maintenance of balance appears to differ with age and the context in which the perturbation to balance occurs. For example, young children who are just learning to stand are more reliant on vision than are older children who have had considerable experience in walking (e.g., Woollacott 56 Shurnway—Cook, 1990). In contrast, regard— less of age, when a person is standing on a narrow surface (e.g., a balance beam) and balar sion balar ence, The ' priat dime nal a gani: respi bilitj one: eral, to e) as p are E bod: The are 3 base men lOWI chili gene and and Shu [DOE fOlll Alt. terr tior ulu a within which the ility, or a fall (gen- edial—lateral direc~ ic balance refers to )port during quiet 3 known as “mov— gravity and base of :enter of gravity is :ps). The processes )ination of the two 3, 1989; Inglin 8C irs when perturba~ p) are unexpected; :r can be predicted king down a flight :tive and anticipa- vidual as he or she ile moving. Vi ., Shumway-Cook Jerspective of bal« subject to external iction). Balance is Function of a num— herai nervous sys- (e.g., strength and , flexibility, bone (e.g., Yim—Chipiis ontrol through its :ee major sensory :tivate the correc— as sensory organi- 30nent of posture! e/postural control rinm of the body 'hat the nature of i of sensory infor- : context in which 3 are just learning had considerable l contrast, regard- alance beam) and Balance and Postural Control 213 balance becomes unstableIinput from the ankle proprioceptors is more critical than vi- sion to restoration of balance (Nashner, 1997). An individual’s capacity for effective balance also depends on a number of other factors, such as attention, previous experi- ence, use of medications, state of mind, and fatigue. MOTOR COORDNATEON ASPECTS OF POSTURE AND BALANQE CONTROL: AN GVERWEW The term motor coordination refers to the timing and sequence of activation of appro- priate postural responses to correct for perturbations to balance. Motor coordination dimensions of postural/balance control provide information about the integrity of spi~ nal and CNS functioning, as well as information important in interpreting sensory or— ganization aspects of posture/balance. The timing, sequence, and control of postural responses represents the postural control system’s plan of action for addressing insta- bility, adapting to it, and bringing the body back into balance. Postural synergies are one form of response organized by the CNS to adjust to instability of the body. In gen- eral, evidence indicates that healthy, young individuals (children and adults) respond to external perturbations to balance by activating stereotyped muscle responses known as postural synergies. These responses involve activation of leg and trunk muscles and are specific to the direction of the induced sway. Muscles on the anterior Surface of the body respond to posterior sway; muscles on the posterior surface to anterior sway. The most commonly studied postural synergy is the “ankle strategy” where responses are generally activated first in the stretched ankle muscles and radiate upward from the base of support in a distal—proximal sequence. Thus, in response to platform move— ment creating anterior sway, the stretched gastrocnemius muscle is activated first, fol- lowed by the hamstrings and then paraspinal muscles. Postural synergies are present in children as young as 15 months, undergo dramatic change from 4 to 6 years, and are generally adult-like by 7 to 10 years of age. Head control, headwtrunk coordination, and development of anticipatory postural adjustments continue to develop to 8 years and beyond {see Nashner, 1977; Shumway—Cook 85 Woollacott, 2001; Woollacott, Shumway-Cook, 85 Williams, 1989). There is general consensus that for adults and most children 7 years or older, the timing and sequence of postural synergies are as follows (e.g., Peterka 36 Black, 1990a, 1990b; Woollacott 85 Jensen, 1996): a 100 millisecond (msec): Center of pressure (COP) moves; passive properties of body biomechanics. a 110 msec: Distal muscle contracts. 9 130—140 msec: Proximal muscle contracts (e.g., 20w30 msec later). a 130 msec: Active torque generation occurs. ' a 230 msec: COP reaches peak displacement. e 260 msec: Peak sway is reached and body returns to upright position. Although the foregoing is rather universally observed in the body’s response to couni teracting sway, other factors can and do affect these synergistic responses to perturba- tions of balance. These include support surface conditions, initial body position, stim— ulus velocity (e.g., the speed with which the platform, for example, is moved), 214 CLINICAL DISORDERS displacement amplitude ’(e.g., the distance that the platform is moved), and problems with the vestibular system and/or the inner ear mechanism, as well as availability and accuracy of visual and proprioceptive information. SENSORY ORGANEZATON Oi: POSTURE/BALANCE QONTROE. Integral to the maintenance and control of posture and balance is the capacity to dc- tect disturbances to stability (Assaiante 8C Amblard, 1995). Detection of perturbations to balance is primarily a function of the visual, proprioceptive, and vestibular systems, Under typical circumstances, all three sources are available and provide accurate and redundant information about the state of equilibrium. This information is integrated and synthesized at higher levels of the nervous system. The nature and importance of each source of sensory input for balance control have been examined through use of an experimental paradigm that involves systematic removal and/or modification of inn puts from the three sensory systems. The typical paradigm requires the individual to stand on a measurement platform under several of the following sensory conditions (Shumway—Cook 8C Horak, 1986; Shurnwawaook Sc Woollacott, 1985): (1) all rele~ vant sources of sensory input are available; (2) proprioceptive and vestibular inputs are available (eyes are closed); (3) vision and vestibular information is available (ankle proprioception is removed or diminished); (4) proprioceptive and vestibular inputs are available along with conflicting visual information (e.g., sensory conflict employing the moving room condition: the walls and ceiling move, the floor does not); (5) vestib- ular information alone is available (eyes are closed and ankle proprioception is con~ trolled for or dampened); and (6) vestibular information is available along with erro— neous visual information (sensory conflict is present and ankle proprioception is reduced or controlled for). The effect of these different sensory conditions on posture/balance control is typi- cally assessed through examination of the change in amplitude or extent of sway. The universal outcome of studies using this paradigm is that balance control is best when- all three sources of sensory information are accurate and available (e.g., redundant sensory conditions). In addition, most studies indicate that while there is some increase in sway when vision is removed, significantly greater increases in sway are observed when either ankle proprioception is eliminated or when conflicting visual information is present. The most dramatic effect on posture/balance (e.g., sway) occurs when ves- tibular information and/or vestibular information coupled with erroneous visual infor mation are the only sources available for detecting sv‘vay. Thus, balance control is most effective when all three sources of sensory input are present and accurate, but control of balance is still possible and reasonably effective when at least two of the three sources of sensory information are available and accurate (e.g., Shumway-Cook 85 Woollacott, 2001). DEVELOPMENT OF POSTURE/BAEANCE CONTRQL For a growing child, good balance is important to a variety of aSpects of development including psychosocial interactions with peers, participation in games and sport activi— ties, and self—esteem. Factors that affect optimal development of posture and balance ou kn , and problems ivailability and NTROl. capacity to dc- f perturbations ibular systems e accurate and in is integrated importance of through use of lification of in- e individual to ory conditions 5): (1) all rele- Wstibular inputs vaiiable (ankle ular inputs are lict employing rot); {5) vestib- :eption is con- ong with erro- uprioception is control is typi~ t of sway. The )l is best when 7 .g., redundant some increase y are observed al information :urs when ves- is visual infor— zontrol is most te, but control 0 of the three EWQY‘COOk 56 f development id sport activi- ‘e and balance Balance and Postural Control 215 _'control may have long-reaching effects that are not immediately obvious but appear much later in development Sensory issues Sensory organization of balance responses in children typically has been examined us— ing a “moving platform” paradigm. The individual stands on a measurement platform embedded in the floor; unexpectedly, the platform is moved forward or backward (or rotated, etc.). This creates a disturbance to balance similar to the start or stop of a bus (or other moving surface) on which the individual is standing. In these circumstances, accurate visual cues derived from sway caused by movement of the platform are avail- able and can be used to assess the nature and extent of the disturbance to equilibrium. I Data from studies (e.g., Butterworth 85 Hicks, 1977; Foster, Sveistrup, 8c Woollacott, 1996; Woollacott, Debu, 85 Mowatt, 1987) using this approach have shown that vi- sual input has little or no effect on the timing of postural synergies (latencies: 90*120 " - msec) in young children (as young as 2 years with some experience in standing/walk- __ing) or adults (Sundermeir, Woollacott, Jensen, 5C Moore, 1996,; Woollacott et al., 1987). . What effect does vision have on postural synergies in infants younger than 2 years of age? Sundermier and Woollacott (1998) categorized chiidren by developmental lev- -- els: (1) “pull to stand” (7—9 months old who could pull the body with some assistance to a standing position) and (2) “newly walking” (13 months old with 4—8 weeks of walking experience) and tested them with “eyes open” and “eyes closed” on a moving " platform. They examined both the latency of onset of gastrdcnemius muscle activity and integrated electromyography (EMG). Data indicated that vision had little or no ef— fect on the speed with which postural responses were activated. This suggests that dur- . ing development, vision may be more involved with activation of slower acting path— ways integral to maintaining posture/balance (e.g., those with latencies greater than 200 msec). Results of this same study indicated that there were developmental differences in the effects of vision on amplitude of muscle activity (integrated EMG). Vision had no measurable effect on the amplitude or force of postural responses in 7—9-month—olds; in contrast for “newly walking” children, the amplitude of activity in the gastrocne- mius muscle was significantly greater with vision than without. These data suggest that vision may play an important role in behavioral transitions that involve new chal- lenges to balance associated with, for example, learning to sit, stand, and/or walk in— dependently. Once the child gains experience and has acquired some mastery of these behaviors, the effect of vision seems to be minimized leg, Butterworth 8c Hicks, 1977; Woollacott 85 Sveistrup, 1992, 1994). Since the elevated activity observed in the gastrocnemius in “new walkers” when vision was present was greater than was func- tionally necessary to maintain balance, it may be that vision, under certain circums stances, acts to amplify proprioceptive—mediated responses that are necessary to adapt to new and different perturbations to balance. Visual information seems not to significantly affect the speed of automatic pos— tural responses (latency : 90—100 msec) in children or adults; however, the sway of in- fants just iearning to stand and/or walk is strongly affected by the presence of errone— ous visual cues. Typically, conflicting visuai cues are created through the paradigm known as the “moving room” phenomenon. This environment creates erroneous vie 216 CLINICAL DISORDERS sual information about sway (e.g., with regard to whether or not sway is occurring and the direction of sway). The individual, young or old, typically sways in concert with the room as visual input from the moving room indicates that the body is sway- ing in the direction opposite to the actual direction of Sway. Most children and espe— cially older adults show increased sway under these conditions. In addition, the magm; tude and direction of this sway actually leads to falls in many individuals. This 1 suggests that the young postural control system is reliant on vision and finds it difficult to ignore or suppress visual information even when it is inaccurate and may lead to in- creased instability. Once the chiid has some experience in walking the magnitude of the sway response to conflicting visual cues declines; however, this sway response is still present in adults (cg, Sundermier et al., 1996). Thus, the development of postural control in children is characterized by changes in the contribution of different sensory systems to balance and by enhanced integrative processes (e.g., Butterworth 8C Hicks, 1977', Forssberg 5C Nashner, 1982). Clearly, al~ though vision is an important source of sensory input for postural control in young children, by 4 to 6 years proprioceptive inputs gain influence and integrative processes begin to emerge. With continued growth and development, children also display an ink creasineg greater capacity to substitute one source of sensory information for an— other (e.g., proprioceptive input for vision) (Shumway-Cook Sc Woollacott, 1985; Woollacott, Shumway-Cook, 85 Nashner, 1986) and to resolve “sensory conflict” (e.g., to su...
View Full Document

{[ snackBarMessage ]}