Here is some valuable research information which further militates against the simplistic claims being made by the Ball, core stability, wobble-board and balancing brigades. The first reference is especially interesting because it reveals vital information on the specificity and mulitifacted nature of balance and the mechanisms underlying balance and stabilisation. By using two force plates (essentially sophisticated bathroom scales which measure forces and torques in all directions), the researchers showed that balance not only is situation specific, but that it also involves MANY combinations of ankle and hip mechanisms. For example, if you stand with feet side-by-side in the same plane, forwards-backwards balance is totally under ankle (plantar/dorsiflexor) control, whereas sideways balance is under hip (abductor/adductor) control. If you feet are in tandem position, or one behind the other in the same plane, then forwards-bacwards balance is dominated by hip mechanisms, with mixed and small or sometimes negligible contributions by the ankle plantar/dorsiflexors. In this stance, for sideways balance, the reverse situation takes place - ankle invertors/evertors dominate, with mixed and small contribution from hip mechanisms. In an in-between 45 degrees stance position, both ankle and hip mechanisms contribute to the net balance control in several totally different ways. Now, these are the many balancing scenarios which take place if you are trying to maintain static stance, but, once your proceed into dynamic stabiilisation, the situation becomes even more complex and simplistic ball and wobble board balancing drills cannot hope to provide the necessary skill training to ensure transfer to daily life and sport. --------------------------------- ABTRACTS <Unified theory regarding A/P and M/L balance in Quiet Stance. Winter DA, Prince F, Frank JS, Powell C, Zabjek KF J Neurophysiol 1996 Jun;75(6):2334-43 Control of posture in quiet stance has been quantified by center of pressure (COP) changes in the anterior-posterior (A/P) and medial-lateral (M/L) directions from a single force platform. Recording from a single force platform, researchers are unable to recognize two separate mechanisms that become evident when two force platforms are used. Depending on the stance position taken, many combinations of an ankle mechanism and a hip (load/unload) mechanism are evident. In side-by-side stance, A/P balance is totally under ankle (plantar/dorsiflexor) control, whereas M/L balance is under hip (abductor/adductor) control. In tandem stance, the A/P balance is dominated by the hip mechanism, with mixed and small or sometimes negligible contributions by the ankle plantar/dorsiflexors: for M/L balance, the reverse is evident; ankle invertors/evertors dominate, with mixed and small contribution from the hip load/unload mechanism. In an intermediate 45 degrees stance position, both ankle and hip mechanisms contribute to the net balance control in totally different ways. In the M/L direction the two strategies reinforce, whereas in the A/P direction the ankle mechanism must overcome and cancel most of the inappropriate contribution by the hip load/unload mechanism. A spatial plot of the separate mechanisms reveals the fact that the random-looking COP scatter plot is nothing more than a spatial and temporal summation of two separate spatial plots. A straight line joining the individual COPs under each foot is the load/unload line controlled by the hip mechanism. At right angles to this load/unload line in the side-by-side and tandem positions is the independent control line by the ankle muscles. In an intermediate standing position, the separate control lines exist, but now the ankle control is not orthogonal to the load/unload line; rather, it acts at an angle of approximately 60 degrees. The direction of these ankle control and load/unload lines also allows us to pinpoint the muscle groups responsible at the ankle and hip in any of the stance. > ----------------- Feedforward ankle strategy of balance during quiet stance in adults. Gatev P, Thomas S, Kepple T, Hallett M J Physiol 1999 Feb 1;514 ( Pt 3):915-28 1. We studied quiet stance investigating strategies for maintaining balance. Normal subjects stood with natural stance and with feet together, with eyes open or closed. Kinematic, kinetic and EMG data were evaluated and cross-correlated. 2. Cross-correlation analysis revealed a high, positive, zero-phased correlation between anteroposterior motions of the centre of gravity (COG) and centre of pressure (COP), head and COG, and between linear motions of the shoulder and knee in both sagittal and frontal planes. There was a moderate, negative, zero-phased correlation between the anteroposterior motion of COP and ankle angular motion. 3. Narrow stance width increased ankle angular motion, hip angular motion, mediolateral sway of the COG, and the correlation between linear motions of the shoulder and knee in the frontal plane. Correlations between COG and COP and linear motions of the shoulder and knee in the sagittal plane were decreased. The correlation between the hip angular sway in the sagittal and frontal planes was dependent on interaction between support and vision. 4. Low, significant positive correlations with time lags of the maximum of cross-correlation of 250-300 ms were found between the EMG activity of the lateral gastrocnemius muscle and anteroposterior motions of the COG and COP during normal stance. Narrow stance width decreased both correlations whereas absence of vision increased the correlation with COP. 5. Ankle mechanisms dominate during normal stance especially in the sagittal plane. Narrow stance width decreased the role of the ankle and increased the role of hip mechanisms in the sagittal plane, while in the frontal plane both increased. 6. The modulation pattern of the lateral gastrocnemius muscle suggests a central program of control of the ankle joint stiffness working to predict the loading pattern. ----------------------- This article reveals major differences in stabilisation strategy if you weight is on one foot at any given instant, a situation which confronts the athlete and average person whenever they walk, run or take part in most land-based sports. Note the emphasis placed not on the much-vaunted "critical core stabilisation" or "core strength", but on vital peripheral mechanisms. Postural control in single-limb stance. Tropp H, Odenrick P J Orthop Res 1988;6(6):833-9 Postural control in single-limb stance has previously been shown to be impaired among soccer players with functional instability (FI) of the ankle joint. The aim of the present study was to further study the role of the ankle in postural control. A dynamic method was used involving optoelectronic movement recordings of body segments and force-plate recordings of the reaction ground force. Surface electromyography was recorded for the peroneus longus muscle. Thirty physically active men were selected. Fifteen of them had FI of the ankle chosen for recording. The results show that different patterns exist for maintaining equilibrium in single-limb stance. The ankle has a central role for postural corrections. The position of center of pressure is highly correlated to the position of the ankle and peroneal muscle activity. When the body was in disequilibrium, corrections were made at the hip. It is proposed that a change from an inverted pendulum model to a multisegmental chain model takes place when adjustments at the ankle joint no longer suffice to maintain postural control. The men with FI showed impaired postural control associated with increased upper segmental corrections. ---------------------- Here is an article which examines the role played by the central nervous system in quiet standing balance. Stiffness control of balance in quiet standing. Winter DA, Patla AE, Prince F, Ishac M, Gielo-Perczak K J Neurophysiol 1998 Sep; 80(3):1211-21 Our goal was to provide some insights into how the CNS controls and maintains an upright standing posture, which is an integral part of activities of daily living. Although researchers have used simple performance measures of maintenance of this posture quite effectively in clinical decision making, the mechanisms and control principles involved have not been clear. We propose a relatively simple control scheme for regulation of upright posture that provides almost instantaneous corrective response and reduces the operating demands on the CNS. The analytic model is derived and experimentally validated. A stiffness model was developed for quiet standing. The model assumes that muscles act as springs to cause the center-of-pressure (COP) to move in phase with the center-of-mass (COM) as the body sways about some desired position. In the sagittal plane this stiffness control exists at the ankle plantarflexors, in the frontal plane by the hip abductors/adductors. On the basis of observations that the COP-COM error signal continuously oscillates, it is evident that the inverted pendulum model is severely underdamped, approaching the undamped condition. The spectrum of this error signal is seen to match that of a tuned mass, spring, damper system, and a curve fit of this "tuned circuit" yields omega n the undamped natural frequency of the system. The effective stiffness of the system, Ke, is then estimated from Ke = I omega n2, and the damping B is estimated from B = BW X I, where BW is the bandwidth of the tuned response (in rad/s), and I is the moment of inertia of the body about the ankle joint. Ten adult subjects were assessed while standing quietly at three stance widths: 50% hip-to-hip distance, 100 and 150%. Subjects stood for 2 min in each position with eyes open; the 100% stance width was repeated with eyes closed. In all trials and in both planes, the COP oscillated virtually in phase (within 6 ms) with COM, which was predicted by a simple 0th order spring model. Sway amplitude decreased as stance width increased, and Ke increased with stance width. A stiffness model would predict sway to vary as Ke-0.5. The experimental results were close to this prediction: sway was proportional to Ke(-0.55). Reactive control of balance was not evident for several reasons. The visual system does not appear to contribute because no significant difference between eyes open and eyes closed results was found at 100% stance width. Vestibular (otolith) and joint proprioceptive reactive control were discounted because the necessary head accelerations, joint displacements, and velocities were well below reported thresholds. Besides, any reactive control would predict that COP would considerably lag (150-250 ms) behind the COM. Because the average COP was only 4 ms delayed behind the COM, reactive control was not evident; this small delay was accounted for by the damping in the tuned mechanical system. --------------------- Like the above research, the following article showed that the first strategy used to maintain balance is provided by muscle stiffness, not reflex-activated muscle activity. Balance recovery from medio-lateral perturbations of the upper body during standing. Rietdyk S, Patla AE, Winter DA, Ishac MG, Little CE J Biomech 1999 Nov; 32(11):1149-58 Postural control strategies have in the past been predominantly characterized by kinematics, surface forces, and EMG responses (e.g. Horak and Nashner, 1986, Journal of Neurophysiology 55(6), 1369-1381). The goal of this study was to provide unique and novel insights into the underlying motor mechanisms used in postural control by determining the joint moments during balance recovery from medio-lateral (M/L) perturbations. Ten adult males received medio-lateral (M/L) pushes to the trunk or pelvis. The inverted pendulum model of balance control (Winter et al., 1998, Journal of Neurophysiology 80, 1211-1221) was validated even though the body did not behave as a single pendulum, indicating that the centre of pressure (COP) is the variable used to control the centre of mass (COM). The perturbation magnitude was random, and the central nervous system (CNS) responded with an estimate of the largest anticipated perturbation. The observed joint moments served to move the COP in the appropriate direction and to control the lateral collapse of the trunk. The individual joints involved in controlling the COP contributed differing amounts to the total recovery response: the hip and spinal moments provided the majority of the recovery (approximately 85%), while the ankles contributed a small, but significant amount (15%). The differing contributions are based on the anatomical constraints and the functional requirements of the balance task. The onset of the joint moment was synchronous with the joint angle change, and occurred too early (56-116 ms) to be result of active muscle contraction. Therefore, the first line of defense was provided by muscle stiffness, not reflex-activated muscle activity. ----------------------- The following research on older adults showed that ankle dorsiflexor and hip extensor forces were lower in individuals reporting falls, and force of the ankle dorsiflexors was a reliable predictor of predicted fall status. Note, once again, that the emphasis was on peripheral processes rather than on "core stability", so why is there all of this overemphasis on the core, when it is well known that standing and locomotory balance depends to a critical extent on peripheral factors? Lower-extremity muscle force and balance performance in adults aged 65 years and older. Daubney ME, Culham EG Phys Ther 1999 Dec;79(12):1177-85 BACKGROUND AND PURPOSE: Measures of postural control may be useful for determining fall risk in older people and for determining the outcomes of treatments aimed at improving balance. Commonly used tools measure the output of the postural control system. The purpose of this study was to determine the degree to which one component of postural control (muscle force) contributes to scores on 3 functional balance measures. SUBJECTS: Fifty community-dwelling volunteers between 65 and 91 years of age participated. Based on their histories, 11 subjects were classified as being at risk for falling. METHODS: Measures were the Berg Balance Scale (BBS), the Functional Reach Test (FRT), and the Timed Get Up & Go Test (GUG). The force generated by 12 lower-extremity muscle groups was measured using a handheld dynamometer. RESULTS: In the group reporting no falls, dorsiflexor and subtalar evertor force accounted for 58% of the score on the BBS, ankle plantar-flexor and subtalar invertor force accounted for 48.4% of the score on the GUG, and ankle plantar-flexor force accounted for 13% of the score on the FRT. Ankle dorsiflexor and hip extensor forces were lower in subjects reporting falls, and force of the ankle dorsiflexors predicted fall status. CONCLUSION AND DISCUSSION: Distal muscle force measures may be able to contribute to the prediction of functional balance scores; however, the muscles involved in the prediction differ depending on the measure of balance. --------------------- The following research, like some of the above articles, also showed the different involvement of hip and ankle balancing strategies. It also found that musculoskeletal mechanics dictate that independent control of joints is relatively difficult to achieve, and that the movement strategy necessary to maintain stability without relying on the "stepping reflex" is rather restricted. Human standing posture: multi-joint movement strategies based on biomechanical constraints. Kuo AD, Zajac FE Prog Brain Res 1993; 97: 349-58 We developed a theoretical framework for studying coordination strategies in standing posture. The framework consists of a musculoskeletal model of the human lower extremity in the sagittal plane and a technique to visualize, geometrically, how constraints internal and external to the body affect movement. The set of all feasible accelerations (i.e., the "feasible acceleration set" or FAS) that muscles can induce at positions near upright were calculated. We found that musculoskeletal mechanics dictate that independent control of joints is relatively difficult to achieve. When muscle activations are constrained so the knees stay straight, to approximate the typical postural response to perturbation, the corresponding subset of the feasible acceleration set greatly favors a combination of ankle and hip movement in the ratio 1:3 (called the "hip strategy"). Independent control of these two joints remains difficult to achieve. When near the boundary of instability, the orientation and shape of this subset show that the movement strategy necessary to maintain stability, without taking a step, is quite restricted. Hypothesizing that regulation of center-of-mass position is crucial to maintaining balance, we examined the feasible set of center-of-mass accelerations. When the knees must be kept straight, the acceleration of the center of mass is severely limited vertically, but not horizontally. We also found that the "ankle strategy", involving rotation about the ankles only, requires more muscle activation than the "hip strategy" for a given amount of horizontal acceleration. Our model therefore predicts that the hip strategy is most effective at controlling the center of mass with minimal muscle activation ("neural effort"). ---------------------------- This article, among other issues, showed that improvement of the upright stance by additional visual feedback is mainly mediated through activation of postural muscles at the ankle level, or ankle strategy. Once again, note the role of peripheral processes in stabilisation of the body. Visual control of human stance on a narrow and soft support surface. Krizkova M, Hlavacka F, Gatev P Physiol Res 1993;42(4):267-72 The influence of additional visual feedback (VF) on stance control was studied under conditions of changed afferent information from the foot sole and ankle joint due to different support surfaces. The changes of body sway amplitudes were analyzed and their frequency spectrum was established. The effect of visual feedback on the amplitude and frequency characteristics of human stance was manifested as: (a) a decrease of the mean amplitude of body sway during visual feedback, corresponding to the decrease of power spectrum density (PSD) of stabilograms in the frequency range below 0.05 Hz, (b) an increase of mean velocity of body sway corresponding to the increase of PSD of stabilograms in the frequency range of 0.4-1.5 Hz. The results showed that the improvement of the upright stance by additional visual feedback is mainly mediated through activation of postural muscles at the ankle level, or ankle strategy. The stabilization effect of visual feedback on stance control is slight or negligible if the performance part in ankle joint (narrow support) was reduced. ---------------------------- This article streses the complexity involved in different balancing situations. Central programming of postural movements: adaptation to altered support-surface configurations. Horak FB, Nashner LM J Neurophysiol 1986 Jun; 55(6): 1369-81 We studied the extent to which automatic postural actions in standing human subjects are organized by a limited repertoire of central motor programs. Subjects stood on support surfaces of various lengths, which forced them to adopt different postural movement strategies to compensate for the same external perturbations. We assessed whether a continuum or a limited set of muscle activation patterns was used to produce different movement patterns and the extent to which movement patterns were influenced by prior experience. Exposing subjects standing on a normal support surface to brief forward and backward horizontal surface perturbations elicited relatively stereotyped patterns of leg and trunk muscle activation with 73- to 110-ms latencies. Activity began in the ankle joint muscles and then radiated in sequence to thigh and then trunk muscles on the same dorsal or ventral aspect of the body. This activation pattern exerted compensatory torques about the ankle joints, which restored equilibrium by moving the body center of mass forward or backward. This pattern has been termed the ankle strategy because it restores equilibrium by moving the body primarily around the ankle joints. To successfully maintain balance while standing on a support surface short in relation to foot length, subjects activated leg and trunk muscles at similar latencies but organized the activity differently. The trunk and thigh muscles antagonistic to those used in the ankle strategy were activated in the opposite proximal-to-distal sequence, whereas the ankle muscles were generally unresponsive. This activation pattern produced a compensatory horizontal shear force against the support surface but little, if any, ankle torque. This pattern has been termed the hip strategy, because the resulting motion is focused primarily about the hip joints. Exposing subjects to horizontal surface perturbations while standing on support surfaces intermediate in length between the shortest and longest elicited more complex postural movements and associated muscle activation patterns that resembled ankle and hip strategies combined in different temporal relations. These complex postural movements were executed with combinations of torque and horizontal shear forces and motions of ankle and hip joints. During the first 5-20 practice trials immediately following changes from one support surface length to another, response latencies were unchanged. The activation patterns, however, were complex and resembled the patterns observed during well-practised stance on surfaces of intermediate lengths. ---------------------- Although this article is devoted to comparing two and four limbed balancing strategies in humans, a noteworthy finding is that activation proceeds on one side of the lower limb in a distal to proximal sequence during bipedal stance muscles - not from nearer the core to the extremities, as many core evangelists seem to imply. Stance dependence of automatic postural adjustments in humans. Macpherson JM, Horak FB, Dunbar DC, Dow RS Exp Brain Res 1989;78(3):557-66 This study investigated the effect of initial stance configuration on automatic postural responses in humans. Subjects were tested in both bipedal and quadrupedal stance postures. The postural responses to horizontal translations of the supporting surface were measured in terms of the forces at the ground, movement of the body segments, and electromyographic (EMG) activity. Postural responses to the same perturbations changed with initial stance posture; these responses were biomechanically appropriate for restoring centre of mass. A change in stance configuration prior to platform movement led to a change in both the spatial and temporal organization of evoked muscle activation. Specifically, for the same direction of platform movement, during bipedal stance muscles on one side of the lower limb were activated in a distal to proximal sequence; during quadrupedal stance, muscles on the opposite side of the lower limb were activated and in a proximal to distal sequence. The most significant finding was an asymmetry in the use of the upper limbs and the lower limbs during postural corrections in quadrupedal stance. Whereas antagonists of the upper limb were either co-activated or co-inhibited, depending on the direction of translation, lower limb antagonists were reciprocally activated and inhibited. Human subjects in a quadrupedal stance posture used the lower limbs as levers, protracting or retracting the hips in order to propel the trunk back to its original position with respect to the hands and feet. Postural responses of the subjects during quadrupedal stance were remarkably similar to those of cats subjected to similar perturbations of the supporting surface. Furthermore, the same predominance of lower limb correction is characteristic of both species, suggesting that the standing cat is a good model for studying postural control in humans. -------------------- This article examined the effect of fast arm movements on postural reactions, another consideration that is important in the training of balance skills in the evareg person and athlete. Directional specificity of postural muscles in feed-forward postural reactions during fast voluntary arm movements. Aruin AS, Latash ML Exp Brain Res 1995;103(2):323-32 Healthy subjects performed bilateral fast shoulder movements in different directions while standing on a force platform. Anticipatory postural adjustments were seen as changes in the electrical activity of postural muscles as well as displacements of the center of pressure and center of gravity. Postural muscle pairs of agonist-antagonist commonly demonstrated triphasic patterns starting prior to the first electromyographic (EMG) burst in the prime-mover muscle. Proximal postural muscles demonstrated the largest anticipatory increase in the background activity during movements in one of the two opposite directions (forward or backwards). These changes progressively decreased when movements deviated from the preferred direction and frequently disappeared during movements in the opposite direction. The patterns in distal muscles varied across subjects and could demonstrate larger anticipatory changes during movements forward and backwards as compared to movements in intermediate directions. Bilateral addition of inertial loads to the wrists did not change the general anticipatory patterns, while making some of their features more pronounced. Anticipatory postural adjustments were followed by later changes in the activity of postural muscles, also reflected in the mechanical variables. Changes in leg joint angles revealed a "hip-ankle strategy" during shoulder flexions and an "ankle strategy" during shoulder extensions. The study demonstrates different behaviors of proximal and distal muscles during anticipatory postural adjustments in preparation for fast arm movements. We suggest that the proximal muscles produce a general pattern of postural adjustments, while distal muscles take care of fine adjustments that are more likely to vary across subjects. ---------------------------- The following research showed that there is a strong relationship of lower extremity strength to balance and gait, so that, once again, we have to ask why there currently is such an exaggerated emphasis on "core strength" and "core stability". Strength is a major factor in balance, gait, and the occurrence of falls. Wolfson L, Judge J, Whipple R, King M J Gerontol A Biol Sci Med Sci 1995 Nov;50 Spec No:64-7 We studied the effects of lower extremity strength as well as gait and balance on the occurrence of falls in nursing home residents. Nursing home residents with a history of falls had less than half of the knee and ankle strength of nonfalling subjects residing in the same home. The differences were more prominent at the ankle than the knee, and were most pronounced in the ankle dorsiflexors, where they were one-tenth that of controls. Also of note was the fact that this same group of fallers had slowed gait velocity (58% of control) as well as an impaired response to postural perturbation as determined on the Postural Stress Test (55% of control). In a recently completed study we measured strength as balance (EquiTest balance platform) of community-dwelling subjects. The occurrence of loss of balance during the sensory organization test was correlated with diminished lower extremity as well as ankle dorsi and plantar flexion moments. Using a logistic regression model, we demonstrated an independent effect of strength on the odds ratio of an SOT-LOB; for each newton-meter per kg increase in strength there was a 20% decrease in the odds ratio. The data from both nursing home and community-dwelling subjects indicate a strong relationship of lower extremity strength to balance and gait. The nursing home studies demonstrated an association between these functions and the occurrence of falls. ----------------------- Dr Mel C Siff Denver, USA http://groups.yahoo.com/group/Supertraining/