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/
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