ArticlePDF AvailableLiterature Review

The Impact of Instability Resistance Training on Balance and Stability

Authors:

Abstract

The most predominant literature regarding balance has emphasised the physiological mechanisms controlling stability. Topics range from extrinsic factors (environment) to intrinsic factors (i.e. muscle coordination, vestibular response). Balance is achieved through an interaction of central anticipatory and reflexive actions as well as the active and passive restraints imposed by the muscular system. However, less research has attempted to document the effects of balance on performance measures (i.e. force, power). Furthermore, short- and long-term adaptations to unstable environments need more substantial research. While force and other performance measures can be adversely affected by a lack of balance, the transferability of instability training to activities of daily living and sport is not precisely known. The applicability of instability and resistance training using unstable platforms or implements may have strong relevance in a rehabilitative or athletic setting. Therefore, a comprehensive review of the literature in this area may possibly be of benefit to practitioners who deal with the general population, athletes or persons debilitated by balance and/or stability disabilities.
Sports Med 2005; 35 (1): 43-53
R
EVIEW
A
RTICLE
0112-1642/05/0001-0043/$34.95/0
2005 Adis Data Information BV. All rights reserved.
The Impact of Instability Resistance
Training on Balance and Stability
Kenneth Anderson and David G. Behm
School of Human Kinetics and Recreation, Memorial University of Newfoundland, St John’s,
Newfoundland, Canada
Contents
Abstract .....................................................................................43
1. Mechanics of Posture .....................................................................44
1.1 Proprioceptive and Peripheral Control ..................................................44
1.2 Central Processing: Anticipatory Postural Adjustments ....................................45
2. Effect of Stable Resistance Training on Balance ..............................................46
3. Stabilising Function of Muscle...............................................................47
3.1 Local and Global Trunk Stabilisation ....................................................47
4. Effect of Instability Training on Trunk Musculature .............................................48
5. The Effects of Instability on Muscle Force and Activation ......................................49
6. Resistance Training ........................................................................50
7. Conclusions ..............................................................................51
The most predominant literature regarding balance has emphasised the physio-
Abstract
logical mechanisms controlling stability. Topics range from extrinsic factors
(environment) to intrinsic factors (i.e. muscle coordination, vestibular response).
Balance is achieved through an interaction of central anticipatory and reflexive
actions as well as the active and passive restraints imposed by the muscular
system. However, less research has attempted to document the effects of balance
on performance measures (i.e. force, power). Furthermore, short- and long-term
adaptations to unstable environments need more substantial research. While force
and other performance measures can be adversely affected by a lack of balance,
the transferability of instability training to activities of daily living and sport is not
precisely known. The applicability of instability and resistance training using
unstable platforms or implements may have strong relevance in a rehabilitative or
athletic setting. Therefore, a comprehensive review of the literature in this area
may possibly be of benefit to practitioners who deal with the general population,
athletes or persons debilitated by balance and/or stability disabilities.
There has been an increasing awareness of the ment system. The mechanisms of human motion
importance and relevance of the specialised and have largely been studied under simplified move-
integrated action of the muscular system in main- ment conditions.
[1-4]
By analysing single-joint
taining posture and optimal function of the move- movements, such principles as force production,
44 Anderson & Behm
force or torque due to joint positions, muscle ments of body position to keep the centre of gravity
mechanics and the synchronisation of muscle activi- over the base of support. The smaller the base, the
ty, studies have described the basic features of more accurate such adjustments must be to maintain
human movement. In the more complex motion of balance. It is proposed that the differential effect of
bi-articular movements, findings have not precisely postural instability on balance could be accounted
substantiated those results found with single-joint for by two main mechanisms: (i) those related to the
movements.
[5]
The complexity of multi-articular alteration of proprioceptive messages at the periph-
movements underlies the difficulty in formulating eral level; and (ii) those related to the central
training exercises and programmes to improve per- processing.
[6]
formance requiring dynamic balance.
Neuromuscular mechanisms play an important
1.1 Proprioceptive and Peripheral Control
role in balance not only when motionless but also
Optimal control of balance in upright posture is
during movement. The human body is not a rigid
an essential requirement for sport, daily activities, or
unit, as it is capable of changing shape, thereby
for the prevention of injury. Stabilisation of postural
complicating some of the simple principles of bal-
equilibrium is achieved by continuous afferent and
ance normally applied to inanimate objects. Moving
efferent control strategies within the sensorimotor
a human body through three dimensions at differing
system with feedback from somatosensory, vestibu-
velocities and while experiencing varying torques
lar and visual inputs.
[7]
For example, viscoelastic
and forces places great demands on the strength,
forces inherent to the ankle muscles correct per-
endurance and coordination of the system. A less
turbations to the upright posture in humans provided
than efficient neuromuscular system may not adapt
the ankle rotation is small.
[8]
For larger displace-
well to the stresses resulting in impaired perform-
ments, active contractions are required if balance is
ance and injury. Trunk stability is an essential com-
to be maintained. The literature identifies that these
ponent for providing a solid base or core to exert or
contractions could originate from stretch or ves-
resist forces. It is still uncertain what type of training
tibulospinal reflexes, or be a voluntary response
is most effective for improving trunk and joint sta-
triggered by multimodal sensory inputs.
[9]
It has
bility in its roles in the prevention of injury and its
been postulated that a confluence of trunk and up-
contribution to balance and force output. As balance
per-leg proprioceptive input establishes the basic
and stability have a functional role for vocational
timing of automatic, triggered balance corrections,
purposes, recreation, daily tasks or injury prevention
which is then preferentially weighted by vestibular
and rehabilitation, it would be beneficial to identify
modulation in muscles that prevent falling.
[10]
While
if a particular exercise regimen and/or technique
human postural control is shared among the vestibu-
could maximise dynamic balance and the ability to
lar, visual and somatosensory systems, the vestibu-
exert forces while maintaining balance. As a number
lar system is considered the main control system for
of neuromuscular mechanisms responsible for bal-
a vertical detector.
[11]
ance exist within the human body, we must first
The afferent information is processed in the
attempt to identify and then understand these partic-
brainstem and cerebellum, followed by the initiation
ular mechanisms and the movement considerations
of motor commands to maintain balance. Unstable
involved. The objective of this paper is to review the
environments stress sensory and motor feedback
literature concerning the need or desirability of un-
loops resulting in increased body sway and muscle
stable environments for training.
activity.
[12]
Standing on an unstable support calls
upon higher levels of the control system and re-
1. Mechanics of Posture
quires an essential change in the mode of utilisation
The apparently simple act of standing motionless of incoming proprioceptive information. This theory
is actually a continuing process of minute adjust- of postural mechanisms was investigated while
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Impact of Instability Resistance Training 45
standing on a rigid floor and varied amplitude ‘see- when they were performed from an initial unipedal
saws’.
[13]
Electromyographic (EMG) activity of the
posture (unstable).
soleus and tibialis anterior during standing on the
Lynn and Woollacott
[17]
found that during quiet
rigid floor and on a see-saw resembled each other.
stance without support, EMG activity was clearly
However, during standing on the more unstable see-
evident from the soleus, therefore, identifying the
saw, the amplitude of the movement in the ankle
role the soleus muscle had in maintaining standing
joint was larger and a marked modulation of the
posture. In their study, measuring EMG activity of
EMG activity of the soleus muscle was observed.
the muscles of the lower limb, they found that when
These results suggest that directionally specific tor-
the subjects were unstable, both the tibialis anterior
que changes in response to centre of gravity shifts
and soleus muscle would fire before any movement
provide important information for maintenance of
would occur. However, during the same task but
posture.
while under a stable condition (holding on to sup-
ports), the activity prior to the movement phase was
abolished. Other results with an unstable base show
1.2 Central Processing: Anticipatory
the occurrence of an early inhibition of the EMG
Postural Adjustments
activity of the triceps surae muscles in advance of
their bursting activity leading into the intended
To achieve the primary goal of a given task, the
movement. Also, the occurrence of an early increase
fundamental role of the central nervous system is to
in triceps surae EMG activity before the voluntary
coordinate the focal movement. Anticipatory pos-
activation of the tibialis anterior was also identified.
tural adjustments play an important role in maintain-
These phenomena outline a complex pattern of ac-
ing balance during task performance. As a result of
tivities, whereby a muscle’s activity is decreased
the enhanced central drive and the corresponding
just prior to fast activation of the same muscle, or is
augmented gamma motor neuron activity during
enhanced when the only intended command is the
balancing, co-contraction of the muscles involved
contraction of its antagonist. Slijper and Latash
[18]
can be implemented.
[14]
It is known that postural
reported an anticipatory increase in activity of the
adjustments of the trunk or legs may be initiated
tibialis anterior, biceps femoris, erector spinae and
prior to the onset of voluntary movements of the
rectus abdominus when experiencing unstable
trunk or upper limb.
[11]
These postural adjustments
standing. In the soleus and rectus femoris, changes
appear to have the aim of minimising the equilibri-
in the background activity were less pronounced. In
um disturbances provoked by these movements.
the absence of additional support (touch or grasp),
Kornecki et al.
[15]
reported that when the support
arm muscles (wrist flexors/extensors, biceps, tri-
object was unstable, the myopotentials of all the
ceps) tended to show an increase in the background
investigated muscles preceded the instant of force
EMG activity. For these reasons, the authors specu-
application (anticipation). The stabilising muscles
late that these phenomena are anticipatory postural
of the task dominated this specific neuromuscular
adjustments, and serve the purpose of minimising
anticipation. This may be explained by the fact the
the subsequent postural destabilisation.
supporting structures must first be stabilised before
In very stable conditions, the requirements of
a motor movement can be efficiently elicited. In
stabilising posture under the action of transient,
addition, the postural adjustments in a number of
motion-related perturbations are alleviated. On the
different stances were measured and found that
other hand, in very unstable conditions, anticipatory
stabiliser muscles fired approximately 30ms prior to
postural adjustments themselves may be viewed as
movement muscle activation.
[16]
The main result
sources of perturbations, which can move the centre
was that anticipatory postural adjustments were
of mass beyond the decreased area of support. This
large when the lower limb flexions were performed
anticipatory increase in synergistic muscle activity
from an initial bipedal posture (stable) and absent
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
46 Anderson & Behm
was also documented using an inverted pendulum to years) with reduced balance showed that short-term
induce instability of the arm.
[1]
strength and endurance training had no restorative
effect on balance of the study cohort.
[26]
Testing to
When we move, we are usually unaware of the
determine if a strength-training programme can im-
complex neuromuscular processes that control our
prove measures of balance among adults aged 65
posture. The mechanical problem of maintaining
posture is particularly challenging but with internal years (n = 55) was also done.
[27]
At post-test, the
central processing within the cerebellum paralleled
exercisers demonstrated enhanced balance, although
with anticipatory postural adjustments and proprio-
none of the post-test measures were significantly
ceptive feedback (vestibular, visual and somatosen-
different from the control group. Furthermore, a
sory inputs), we are able to meet the constant de-
randomised, controlled trial compared the effects
mands for maintaining posture and balance. While
of resistance training on static balance.
[28]
The
instability resistance training should certainly tax
strength-training group exercised three times per
the proprioceptive control of posture, it has not been
week using exercise machines with balance being
established whether any positive adjustments would
measured on a force platform. Results indicate that
be mediated through anticipatory postural adjust-
double-stance measurements were unchanged after
ments (central processing). There is some literature
training. In single stance, the centre of displacement
to suggest that resistance training under stable con-
of the centre of pressure improved by 17%. Finally,
ditions can improve balance, especially in older
no significant between-group differences for one-
adults.
leg blind balance time suggests that strength training
alone does not appear to enhance standing balance
2. Effect of Stable Resistance Training
in active, community dwelling older adults.
[29]
on Balance
In a study of younger healthy subjects, partici-
pants were assigned to either strength- or balance-
The effect of resistance exercise on muscle
training regimens.
[7]
After 1 month, the training was
strength and size has been clearly documented,
[19-22]
exchanged between groups. At the first follow-up,
but evidence suggests that resistance training, absent
balance training led to significant increase in the
of balance training, also has a positive effect on
performance outcomes of the balance-training
balance. It was found that strength exercises contrib-
group, whereas the strength-training group did not
ute to better balance and gait in women aged 57
(p < 0.001). However, at the second follow-up,
years.
[23]
In a separate study, the mean increase in
scores of both groups were significantly increased
balance scores in a balance-training group was
when compared with baseline.
146% and 34% in the strength-training group (p <
Motor-skill training, including balance training,
0.01).
[24]
A prospective, blinded, randomised trial of
increases the sensitivity of feedback pathways and
moderate intensity strength exercise was conducted
shortens the onset times of the selected muscles by
on 132 older adults.
[25]
They found that gait stability
improved significantly more in the resistance exer- improving the sensitivity of the position sense of
cise group than in the control group. These results
both agonistic and antagonistic muscles.
[7]
The mus-
show that even moderate strength gains (17.6%)
cle, as the termination of the final pathway of the
may benefit gait and balance, thus providing a sound
sensorimotor system, particularly contributes to the
basis for the encouragement of low-intensity
maintenance of body balance. It has been document-
strength training for individuals with functional lim-
ed that resistance training that increased muscular
itations.
strength also increased stability and coordination.
[30]
Improvements in task performance were accompa-
A number of studies were conducted to test if a
nied by changes in the pattern of recruitment of the
training programme can restore balance in older
muscles that were the focus of the resistance-train-
individuals.
[26-29]
The effect of strength and endur-
ance training on balance in older adults (aged 65–85 ing programme. Specifically, the trained muscles
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Impact of Instability Resistance Training 47
were recruited in a more consistent fashion after tractions plays a significant role in stabilising the
training. However increased strength does not guar- shoulder joint.
[32]
antee improved balance. Kollmitzer et al.
[7]
showed
This coordination leads to the extraordinary com-
that strength training actually reversed any benefit
plexity of the nervous system, of which one of the
from the balance training in their study. Training of
most important tasks is to control the stabilisation of
the muscles that contribute to posture may reasona-
the joints’ degrees of freedom unused in a given
bly change not only muscle force output, but also the
motor task by stimulation of antagonistic muscles.
coordination of synergistic and antagonist muscle
Behm et al.
[33]
studied agonist/antagonist relation-
activation. Thus, depending on the specific training
ships of the leg extensors with instability. During leg
programme and population in question (i.e. a frail,
extensions, antagonistic hamstring activity in-
aged individual may benefit more from the benefi-
creased by 29.1% (p = 0.05) under unstable versus
cial effects of increased force output for responding
stable conditions. Milner et al.
[34]
provided evidence
to perturbations), the role of resistance training on
from comparison of forceful flexor and extensor co-
balance is unclear.
contractions that EMG was always less during maxi-
mal co-contractions than it would be as a prime
mover. Slijper and Latash
[18]
demonstrated that dur-
3. Stabilising Function of Muscle
ing standing on an unstable board, there was a
Although much is known about how muscles
tendency for an increase in the background muscle
maintain static equilibrium, little is known how they
activity, which would increase the resting stiffness
maintain dynamic balance when exerting an exter-
or tonus of the muscle in response to the unstable
nal force. Exerting external forces while attempting
platform. Adding manual support typically resulted
to maintain dynamic balance is tantamount to suc-
in decreased background activity. The cost of cop-
cess in the majority of sports and a necessity in the
ing with instability is an increase in co-contractions
activities of daily living (i.e. carrying shopping
resulting in a decrease in external force. However, it
bags, babies). Exerting a force with the upper ex-
can be argued that the task would not be able to be
tremity upon an external object requires coordina-
performed without this co-activation.
tion of the neuromuscular system. This coordination
Thus, this stabilisation process consists of estab-
would ensure the inhibition of some muscles to
lishing active muscular constraints to minimise the
achieve simultaneously coupled motions to take
degrees of freedom within a joint or series of joints
place in other joints. Sporrong et al.
[31]
studied how
and results in stabilisation of the excessive mobility
handgrip exercises/activities increased shoulder
of external objects. Trunk or core stabilisation is
muscle activity. Subjects were asked to perform
essential for maintaining static or dynamic balance
isometric contractions against a handgrip dynamom-
and especially when attempting to exert forces upon
eter. In the supraspinatus and infraspinatus muscles,
external objects. A lack of trunk stabilisation may
there was a positive correlation between the degree
also be a major contributor to the back pain endemic
of the shoulder muscle activity and the intensity of
within our society.
handgrip exertion. This could have practical value in
the rehabilitation of the hand, as not only the mus-
3.1 Local and Global Trunk Stabilisation
cles of the hand and forearm should be rehabilitated,
but also the stabiliser muscles of the shoulder as well Functional joint stability and its effect on balance
for maximal rehabilitation of grip strength. Further- are dependent on integrated local and global muscle
more, muscle activity occurred simultaneously in function.
[35-37]
Comerford and Mottram
[36]
have pro-
muscles producing a movement and in antagonistic posed a classification system for muscle function.
muscles of a number of different shoulder move- They have defined and characterised vertebral mus-
ments (i.e. flexion, extension, adduction, abduc- cles as local stabilisers, global stabilisers and global
tion), showing how coordination due to muscle con- mobilisers. They identify that role of the local sta-
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
48 Anderson & Behm
bilisers is to maintain low force continuous activity Arokoski et al.
[35]
identified that the stability of
the spine was increased with either increased flexor-
in all positions of joint range and in all directions of
extensor muscle co-activation forces or increased
joint motion. Their activity usually increases in an-
intra-abdominal pressure. Deep local stabilising
ticipation to a load and/or movement, thus providing
muscles, especially the multifidus and the transverse
joint protection and support. Global stabilisers gen-
abdominus muscles, mainly contribute to stability.
erate torque and provide control over some motions.
In the investigated exercises, the researchers found
Global mobilisers are required to have adequate
the lumbar multifidus muscle function patterns ap-
length to provide full range of motion around a joint
peared to be coupled with longissimus thoracis mus-
without causing overstrain elsewhere in the move-
cles, thus the local and global back muscle function
ment system; however, they do have a stability role
showed similar activation patterns and simultaneous
under high load or strain. The normal function of the
function.
local muscle system is to provide sufficient segmen-
It has been suggested that back muscle contrac-
tal stability to the spine. The global muscle system
tions as low as 25% of maximal voluntary contrac-
provides general trunk stabilisation and enables the
tion (MVC) are able to provide maximal joint stiff-
static and dynamic work necessary for daily living
ness.
[39]
A low percentage of maximal voluntary
and sport activities.
[38]
The multifidus has been iden-
isometric contraction from the trunk musculature
tified as a local stabilising muscle that acts simulta-
thus stabilises the spine during normal movements
neously with the global muscles (longissimus tho-
and motor control, not just muscle strength is impor-
racis, rectus abdominus).
[35]
One definition of global
tant to dynamic stability training.
[40]
Furthermore,
muscles is that they are muscles that act on the
because lumbar stabilising multifidus muscles are
spinal column via the rib cage (i.e. erector spinae,
mainly composed of type I muscle fibres,
[41]
only
rectus abdominus), which control the overall re-
relatively low loads (approximately 30–40% MVC)
sponse, and local muscles that are attached directly
are needed to improve their effectiveness.
[42]
There-
to the lumbar spine.
[37]
fore, resistance training under unstable conditions
In a study of muscle recruitment patterns during
with relatively high loads may not automatically
asymmetric lifting in healthy individuals, it was
provide a suitable training environment for vertebral
found that the left and right internal obliques, rectus
stability and dynamic balance. On the other hand,
femoris and multifidus showed symmetrical co-con-
the integration of balance and resistance training
traction in all variants of the lifting activities.
[37]
In
may augment motor control while increasing muscle
contrast, significant left/right differences were ob-
activation, strength and stiffness.
served in the external oblique, gluteus maximus,
illiocostalis lumborum pars thoracis and latissimus
4. Effect of Instability Training on
dorsi. These results show a symmetrical activation
Trunk Musculature
of the local muscles during the performance of low
load, asymmetric lifting tasks, which suggest that
It is proposed that training under unstable condi-
these muscles play a stabilising role during these
tions will stress the neuromuscular system to a
manoeuvres. The global muscles, however, show
greater extent than traditional resistance training
asymmetric patterns of activation during the same
methods using more stable benches and
tasks, supporting their role of global stabilisers and
floors.
[12,14,43,44]
Strength gains can be attributed to
prime movers. In addition to these findings, it was
both increases in muscle cross-sectional area and
identified that the multifidus, transverse abdominus
improvements in neuromuscular coordination.
[45]
A
and the internal obliques act as part of the local
number of researchers have reported that neural
stabilising system; whereas the longissimus
adaptations play a vital role in strength gains in
thoracis, rectus abdominis and external obliques
the early portion of a resistance training pro-
constitute a part of the global stabilising system.
[35]
gramme.
[45,46]
In addition, it is suggested that the
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Impact of Instability Resistance Training 49
specific neural adaptations occurring with resistance significantly fewer recurrent sprains. Also, signifi-
cantly fewer patients in a wobble-board training
training are not increased recruitment or activation
group had functional instability of the ankle com-
of motor units, but an improved coordination of
pared with a no wobble-board training group.
[44]
The
agonist, antagonists, synergists and stabilisers.
[47,48]
authors concluded that training on a wobble board
With the current interest in stability training for
was effective in reducing residual symptoms follow-
the injured low back and home fitness equipment
ing ankle ligament trauma compared with no train-
available to the consumer, the use of labile (movea-
ing.
ble) surfaces to challenge the motor control system
Behm and colleagues
[52]
had subjects perform a
is becoming more popular. However, this could be
variety of typical trunk strengthening exercises
of concern as little is known about the effects of
under stable and unstable (Swiss ball) conditions.
these unstable surfaces on muscle activity.
Overall, activation of the lumbo-sacral and upper
To maximise functional performance, individu-
lumbar erector spinae as well as the deep abdominal
als should attempt to train in an environment that
stabilisers was significantly greater with the unsta-
mimics their real-world situation. Often in sport and
ble condition. Thus, the very few investigations of
activity, the individual is not in a stationary, stable
unstable exercises on trunk muscle activation seem
position, therefore, numerous training aids have
to concur that the introduction of instability into the
been developed to simulate these real-world situa-
activity increases the extent of muscle activation.
tions. One of these training aids is the ‘Swiss ball’.
Siff
[49]
found that the Swiss ball provided a wider
5. The Effects of Instability on Muscle
range of movement (with an optimal starting posi-
Force and Activation
tion from a few degrees of active trunk extension),
which he described as preferable to similar actions
Unstable platforms or loads can lead to increased
performed in most circuit training gyms. The impor-
stabilisation functions at the expense of motive or
tance of ‘Swiss balls’ in a rehabilitative setting has
force functions.
[48,53]
Thus, even with substantial
been documented in the re-education of postural
force decrements, overall muscle activation may
muscles and to facilitate movement and postural
remain virtually unchanged. Kornecki et al.
[15]
found
reactions in neurologically impaired patients.
[50]
that contributions of stabilising muscles increased
on average by 40% when the handle changed from
Vera-Garcia et al.
[51]
tested the type of surface
stable to unstable during pushing movements They
(stable or unstable) on the muscle mechanics of the
showed that the process of muscular stabilisation of
abdominal wall. They indicated that performing
the investigated joint caused, on average, 30% drops
curl-up exercises on an unstable surface increased
in force, velocity and power (p < 0.01). Instability-
abdominal muscle activity. EMG analysis showed
induced muscular stabilisation of the wrist joint
the rectus abdominus muscle activity on a stable
caused a significant increase in the EMG contribu-
surface was 21% of the MVC and external oblique
tions of the stabilising muscles and a visible drop in
muscle activity was 5% of MVC. For the curl-up on
the contributions of the muscles that realised motor
an unstable ball, rectus abdominus activity was 35%
functions, which in turn bring about a significant
of MVC and external oblique muscle activity was
loss of maximum force, velocity and power pro-
10% of MVC. This study suggests a much higher
duced against an external object.
demand on the motor control system when perform-
ing abdominal exercises on labile equipment. In
A number of other authors have examined the
addition, a stability ball training group’s perform-
function of limb stabilising muscles. It was found
ance in trunk flexion and back extension improved
that both the short and long heads of the bicep have
significantly more (p < 0.05) than either the tradi-
similar functions as anterior stabilisers of the gle-
tional group or the controls.
[50]
Possible rehabilita-
nohumoral joint and their roles in stabilisation in-
tive benefits were suggested with the occurrence of
crease as joint stability decreases.
[54]
The stabilising
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
50 Anderson & Behm
function of scapular stabilisers while performing ferent muscles (muscle co-ordination) were identi-
fied. For example, the flexor pollicis longus EMG
push-ups on miniature trampolines was also ex-
was significantly greater during stable opposition
amined.
[55]
They found no significant difference in
pinch whereas EMG activity in the dorsal interos-
stabiliser EMG activity between stable and unstable
seus muscle was significantly greater in the unstable
conditions; however, they acknowledged the degree
condition.
of stability induced by the miniature trampolines
The literature indicates that instability affects
was likely to be insufficient to illicit an unstable
force output in numerous ways (i.e. decreased force
platform.
output, increased co-contractions, altered muscle
Anderson and Behm
[56]
also reported no signifi-
coordination). The goal of instability resistance
cant difference in EMG activity of the pectorals,
training would be to accommodate to an unstable
triceps, latissimus dorsi and rectus abdominus when
environment, and thus hopefully diminish the loss of
performing maximal isometric chest presses under
force and the extent of co-contractions.
stable and unstable conditions. However, maximum
isometric force was decreased by 60% with the
6. Resistance Training
unstable base. They suggested that the decreased
balance associated with resistance training on an
Resistance training can be used to induce
unstable surface might force limb musculature to
strength, power and endurance adaptations with a
play a greater role in joint stability. In a further study
myriad of exercises and equipment that will provide
from the same laboratory, upper lumbar, lumbo-
a spectrum of stable and unstable loads. The range
sacral erector spinae, abdominal stabilisers and
of stable and unstable platforms and loads used
soleus activation were all activated to a greater
during resistance training might also induce motor
extent when performing squats under unstable con-
learning adaptations with the goal of improving
ditions with the same submaximal load.
[57]
The au-
dynamic balance and force outputs while unstable.
thors explained that the increased EMG activity of
Several modes of training are currently available,
these muscles may be attributed to their greater
with some of the more popular methods being the
postural and stabilisation roles with the unstable
use of free-weights, weight stack machines and
condition.
isokinetic devices. Each method has associated free-
In contrast, Behm et al.
[33]
reported that unstable
doms and constraints.
leg extensor and plantar flexor activation averaged
The advantages of free weights over machines
44.3% and 2.9% less, respectively, than during sta-
are well documented.
[59-61]
The major advantages
ble conditions. Unstable leg extensor force was
arise from the ability of free-weight exercises to
70.5% less than stable force while unstable plantar
mimic the movement demands of real-life sport and
flexor force was 20.2% less than its respective stable
everyday activities from the numerous possible vari-
force. They suggested that under conditions of great
ations with free-weight exercises. This use of free
instability, as was experienced with the destabilising
weights is vital in the principles of exercise specific-
torque of unilateral leg extensions performed on a
ity (training in a specific manner to produce a specif-
Swiss ball, increased stabilisation functioning of the
ic outcome). In addition, free-weight lifting requires
muscles was insufficient to maintain balance result-
the lifter to balance and stabilise the bar/dumbbells
ing in decreased overall activation. In contrast, no
in all movement planes. Having the individual lift
statistical difference was found in the magnitude of
dumbbells unilaterally can further augment the in-
forces produced in a stable versus an unstable proto-
stability of free weights. Behm et al.
[52]
reported
col of the thumb musculature (nine separate mus-
greater trunk muscle activation when dumbbell
cles) in individuals using a modified clinical pinch
chest presses were performed unilaterally rather
meter.
[58]
Although force output remained constant
than bilaterally. Further advantages of free weights
between protocols, changes in the activation of dif- include a constant external resistance baseline
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Impact of Instability Resistance Training 51
throughout the particular movement as well as the be experienced with a stability/balance programme,
ability for full body training. The movement of a it would be beneficial for fitness and health practi-
free weight is constrained by the lifter, as opposed to tioners to combine balance training modalities with
a machine, which often does not require the muscles resistance training so their clients, especially if so-
to work in the similar stabilising role.
[62]
matosensory impaired, can maximise the positive
effects of their training time. Although force outputs
In contrast to free weights, most machines create
are diminished under unstable conditions, the de-
a forced or guided one- or two-dimensional move-
creased balance associated with instability resis-
ment pattern for the user opposed to the three-
tance training may force limb and trunk musculature
dimensional movement pattern of free weights. This
to play a greater role in joint stability. The use of
forced pattern does not allow as much movement
unstable platforms as a resistance training modality
freedom in movement patterns partly caused differ-
for strength gains can be employed to allow high
ences in people’s limb lengths, bone articulations
muscle activation levels to be developed through an
and muscle attachment sites. Rubber tubing and
increased reliance on stabilising functions. As this
machines using cables that can move in three dimen-
high level of muscle activation can be achieved with
sions are more adaptable to individual anthropomet-
less resistance, this training modality may have pos-
ric differences. However, cables and rubber tubing
itive implications in progressive muscle and joint
typically offer a fast-to-slow movement pattern,
rehabilitation as well as sport-specific training.
with greater resistance and slower speed toward the
Since most sports involve a combination of stabilis-
end of the movement, which contrasts with the
ing and force producing functions (running forehand
typical slow-to-fast pattern of many sport move-
in tennis, baseball pitcher wind-up, moving slap shot
ments.
[63]
Another disadvantage of machines is that
in hockey and many others), instability resistance
they often provide resistance only at a single joint.
training provides similar challenges to the neuro-
Also, because most machines support the user, few,
muscular system. However, in order to induce maxi-
if any demands are required to stabilise and balance
mum or near maximum overload forces upon the
both the user and/or the load. However, machines do
limbs, a stable platform may be necessary. It is
offer some benefits as they often ensure the correct
recommended that a comprehensive, sport-specific,
range of motion and movement pattern, lowering the
strength-training programme incorporate exercises
likelihood of injury, especially with individuals un-
under both stable and unstable conditions.
familiar to resistance training.
[64]
Numerous authors have attempted to make the
Free-weight exercises are generally agreed upon
connection in identifying the effects of strength
by the fitness community as the most advantageous
training versus balance training on balance; howev-
method of weight training due to the positive effects
er, little research has been done regarding actually
of unstable training protocols on neuromuscular
performing this strength training on stable and un-
function.
[12,14,43]
stable platforms and its resultant effect on balance. It
is now proposed that the scientific community iden-
7. Conclusions
tify which methods and exercises offer the most
It is now evident that a large amount of resistance
benefit with reference to stability and balance while
training information exists stemming from different
offering the highest degree of carry-over into a real-
equipment for varied training regimens. However, it
world setting.
is essential to summarise and apply this knowledge
in a more functional and activity-specific model to
Acknowledgements
identify if a parallel exists for the need, practicality
and importance of stability training.
No sources of funding were used to assist in the prepara-
Through the training-induced functional in-
tion of this review. The authors have no conflicts of interest
creases in balance and muscle coordination that can that are directly relevant to the content of this review.
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
52 Anderson & Behm
control, muscular strength, and cholesterol in type I diabetic
References
men. Diabetes Care 1990; 13 (10): 1039-43
1. Stokes I, Gardner-Morse M. Strategies used to stabilize the
21. Goreham C, Green H, Ball-Burnett M, et al. High-resistance
elbow joint challenged by inverted pendulum loading. J Bi-
training and muscle metabolism during prolonged exercise.
omech 2000; 33 (6): 737-43
Am J Physiol 1999; 276 (3 pt 1): E489-96
2. Gardner-Morse M, Stokes I, Laible J. Role of muscles in lumbar
22. Hakkinen K, Newton R, Gordon S, et al. Changes in muscle
spine stability in maximum extension efforts. J Orthop Res
morphology, electromyographic activity, and force production
1995; 13 (5): 802-8
characteristics during progressive strength training in young
3. Milner T, Cloutier C. Compensation for mechanically unstable
and older men. J Gerontol A Biol Sci Med Sci 1998; 53 (6):
loading in voluntary wrist movement. Exp Brain Res 1993; 94
B415-23
(3): 522-32
23. Lord S, Clark R, Webster I. Physiological factors associated
4. Eloranta V. Coordination of the thigh muscles in static leg
with falls in an elderly population. J Am Geriatr Soc 1991; 39
extension. Electromyogr Clin Neurophysiol 1989; 29 (4):
(12): 1194-201
227-33
24. Heitkamp H, Horstmann T, Mayer F, et al. Gain in strength and
5. Lacquaniti F, Soechting J. Responses of mono- and bi-articular
muscular balance after balance training. Int J Sports Med 2001;
muscles to load perturbations of the human arm. Exp Brain Res
22 (4): 285-90
1986; 65 (1): 135-44
25. Krebs D, Jettte A, Assmann S. Moderate exercise improves gait
6. Ivanenko Y, Solopova I, Levik Y, et al. The direction of postural
stability in disabled elders. Arch Phys Med Rehabil 1998; 79
instability affects postural reactions to ankle muscle vibration
(12): 1489-95
in humans. Neurosci Lett 2000; 292 (2): 103-6
26. Buchner D, Cress M, de Lateur B, et al. The effect of strength
7. Kollmitzer J, Ebenbichler G, Sabo A, et al. Effects of back
and endurance training on gait, balance, fall risk, and health
extensor strength training versus balance training on postural
services use in community living older adults. J Gerontol
control. Med Sci Sports Exerc 2000; 32 (10): 1770-6
1997; 52 (4): M218-24
8. Nashner L. Adapting reflexes controlling the human posture.
27. Topp R, Mikesky A, Wigglesworth J, et al. The effect of a
Exp Brain Res 1976; 26 (1): 59-72
12-week dynamic resistance strength training program on gait
9. Allum J. Organization of stabilizing reflex responses in tibialis
velocity and balance of older adults. Gerontologist 1993; 33
anterior muscles following ankle flexion perturbations of
(4): 501-6
standing man. Brain Res 1983; 264 (2): 297-301
28. Judge J, Lindsey C, Underwood M, et al. Balance improvements
10. Allum J, Honegger F. Interactions between vestibular and pro-
in older women: effects of exercise training. Phys Ther 1993;
prioceptive inputs triggering and modulating human balance-
73 (4): 254-62
correcting responses differ across muscles. Exp Brain Res
29. Schlicht J, Camaione D, Owen S. Effect of intense strength
1998; 121 (4): 478-94
training on standing balance, walking speed, and sit-to-stand
11. Mizuno Y, Shindo M, Kuno S, et al. Postural control responses
performance in older adults. J Gerontol 2001; 56 (5): M281-6
sitting on unstable board during visual stimulation. Acta Astro-
30. Carroll T, Barry B, Riek S, et al. Resistance training enhances
naut 2001; 49 (3): 131-6
the stability of sensorimotor co-ordination. Proc R Soc Lond
12. Nardone A, Schieppati M. Postural adjustments associated with
2001; 268 (1464): 221-7
voluntary contraction of leg muscles in standing man. Exp
31. Sporrong H, Palmerud G, Herberts P. Hand grip increases
Brain Res 1988; 69 (3): 469-80
shoulder muscle activity, an EMG analysis with static hand
13. Ivanenko Y, Levik Y, Talis V, et al. Human equilibrium on
contractions in 9 subjects. Acta Orthop Scand 1996; 67 (5):
unstable support: the importance of feet-support interaction.
485-90
Neurosci Lett 1997; 235 (3): 109-12
32. Kronberg M, Nemeth G, Brostrom L. Muscle activity and
14. Gantchev G, Dimitrova D. Anticipatory postural adjustments
coordination in the normal shoulder: an electromyographic
associated with arm movements during balancing on unstable
study. Clin Orthop 1990; (257): 76-85
support surface. Int J Psychophysiol 1996; 22 (1-2): 117-22
33. Behm D, Anderson K, Curnew S. Muscle force and neuromus-
15. Kornecki S, Kebel A, Siemienski A. Muscular cooperation
cular activation under stable and unstable conditions. J
during joint stabilization, as reflected by EMG. Eur J Appl
Strength Cond Res 2002; 16 (3): 416-22
Physiol 2001; 85 (5): 453-61
34. Milner T, Cloutier C, Leger A, et al. Inability to activate muscles
16. Nouillot P, Bouisset S, Do M. Do fast voluntary movements
maximally during co-contraction and the effect on joint stiff-
necessitate anticipatory postural adjustments even if equilibri-
ness. Exp Brain Res 1995; 107 (2): 293-305
um is unstable? Neurosci Lett 1992; 147 (1): 1-4
35. Arokoski J, Valta T, Airaksinen O, et al. Back and abdominal
17. Lin S, Woollacott M. Postural muscle responses following
muscle function during stabilization exercises. Arch Phys Med
changing balance threats in young, stable, older, and unstable
Rehabil 2001; 82 (8): 1089-98
older adults. J Motor Behav 2002; 34 (1): 37-44
36. Comerford M, Mottram S. Functional stability re-training: prin-
18. Slijper H, Latash M. The effects of instability and additional
ciples and strategies for managing mechanical dysfunction.
hand support on anticipatory postural adjustments in leg, trunk,
Man Ther 2001; 6 (1): 3-14
and arm muscles during standing. Exp Brain Res 2000; 135
37. Kiefer A, Shirazi-Adl A, Parnianpour M. Stability of the human
(1): 81-93
spine in neutral postures. Eur Spine J 1997; 6 (1): 45-53
19. Hortobagyi T, DeVita P. Favorable neuromuscular and cardio-
38. Danneels L, Vanderstraeten G, Cambier D, et al. A function
vascular responses to 7 days of exercise with an eccentric
subdivision of hip, abdominal, and back muscles during asym-
overload in elderly women. J Gerontol Biol Sci Med 2000; 55
metric lifting. Spine 2001; 26 (6): E114-21
(8): B401-10
20. Durak E, Jovanovic-Peterson L, Peterson C. Randomized cross- 39. Cresswell A, Oddsson L, Thorstensson A. The influence of
over study of the effect of resistance training on glycemic sudden perturbations on trunk muscle activity and intra-ab-
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Impact of Instability Resistance Training 53
dominal pressure while standing. Exp Brain Res 1994; 98 (2): 54. Itoi E, Kuechle D, Newman S, et al. Stabilizing function of the
336-41
biceps in stable and unstable shoulders. J Bone Joint Surg
1993; 75 (4): 546-50
40. Vezina M, Hubley-Kozey C. Muscle activation in therapeutic
exercises to improve trunk stability. Arch Phys Med Rehabil
55. Lear L, Gross M. An electromyographical ananlysis of the
2000; 81 (10): 1370-9
scapular stabilizing synergists during a push-up progression. J
Orthop Sport Phys Ther 1998; 28 (3): 146-57
41. Thorstensson A, Carlson H. Fiber types in human lumbar back
muscles. Acta Physiol Scand 1987; 131 (2): 195-202
56. Anderson K, Behm DG. Maintenance of EMG activity and loss
42. Richardson C, Jull G, Hodges P, et al. Therapeutic exercises for
of force output with instability. Can J Appl Physiol 2003; 28
spinal segmental stablization in low back pain. London:
Suppl.: S27
Churchill Livingston, 1999
57. Anderson K, Behm DG. Trunk muscle activity increases with
43. Sheth P, Yu B, Laskowski E, et al. Ankle disk training influ-
unstable squat movements. Can J Appl Physiol 2003; 28
ences reaction times of selected muscles in a simulated ankle
Suppl.: S26
sprain. Am J Sports Med 1997; 25 (4): 538-43
58. Johanson M, Valero-Cuevas F, Hentz V. Activation patterns of
44. Wester J, Jespersen S, Nielson K, et al. Wobble board training
the thumb muscles during stable and unstable pinch tasks. J
after partial sprains of the lateral ligaments of the ankle: a
Hand Surg [Am] 2001; 26 (4): 698-705
prospective random study. J Orthop Sports Phys Ther 1996; 23
(5): 332-6
59. Garhammer J. Free weight equipment for the development of
athletic strength and power: part I. Natl Strength Cond Assoc J
45. Behm D. Neuromuscular implications and applications of resis-
1981; 3 (6): 23-33
tance training. J Strength Cond Res 1995; 9 (4): 264-74
46. Sale D. Neural adaptation to resistance training. Med Sci Sports
60. Stone M. Considerations in gaining a strength-power training
Exerc 1988; 20 (5): S135-45
effect (machines versus free weights): free weights, part II.
Natl Strength Cond Assoc J 1982; 4 (4): 22-54
47. Rutherford O, Jones D. The role of learning and coordination in
strength training. Eur J Appl Occup Physiol 1986; 55 (1):
61. Stone M, O’Bryant H. Weight training: a scientific approach.
100-5
Minneapolis (MN): Burgess International, 1987
48. Kornecki S, Zschorlich V. The nature of stabilizing functions of
62. Baechle T. Essentials of strength and conditioning. Champaign
skeletal muscles. J Biomech 1994; 27 (2): 215-25
(IL): Human Kinetics, 1994
49. Siff M. The functional mechanics of abdominal exercise. South
63. Behm D, Sale D. Velocity specificity of resistance training.
Afr J Sports Med 1991; 6: 15-9
Sports Med 1993; 15 (6): 374-88
50. Stanforth D, Stanforth P, Hahn S, et al. A 10-week training
64. McCaw S, Friday J. A comparison of muscle activity between a
study comparing Resistaball and traditional trunk training. J
free weight and machine bench press. J Strength Cond Res
Dance Med Sci 1998; 2 (4): 134-40
1994; 8 (4): 259-64
51. Vera-Garcia F, Grenier S, McGill S. Abdominal muscle re-
sponse during curl-ups on both stable and labile surfaces. Phys
Ther 2000; 80 (6): 564-9
Correspondence and offprints: Dr David G. Behm, School of
52. Behm DG, Leonard A, Young W, et al. Trunk muscle EMG
Human Kinetics and Recreation, Memorial University of
activity with unstable and unilateral exercises. Can J Appl
Newfoundland, St Johns, Newfoundland A1C 5S7, Cana-
Physiol 2003; 28 Suppl.: S30
da.
53. Kornecki S. Mechanism of muscular stabilization process in
joints. J Biomech 1992; 25 (3): 235-45
E-mail: dbehm@mun.ca
2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
... When examining the upper limbs, improvements were mixed (Table 4), where CF improved in all three directions for all time points, while TRAD only observed improvements at T2, and LM failed to show any improvement. Anderson and Behm (2005) summarized from the literature that stable resistance training without integrating the balance factor has also a positive effect on the general balance of the body. Additionally, they cite the importance of the use of free weights to develop balance, which was greatly implemented in both CF and TRAD programming. ...
... As the MVIC was only a 4-second duration, impairments to focus and concentration would probably not have a substantial impact on corticospinal excitability or muscle activation. . When balance is perturbed, the system needs to respond quickly (reaction time) with appropriate muscle contractile force (strength) to offset the perturbation (Anderson and Behm 2005). While RFD was adversely affected, muscle strength (MVIC peak force) and reaction time were not signi cantly impaired by the cannabis inhalation, which generally seemed su cient to maintain a similar duration of balance in three of the four tests. ...
Preprint
Full-text available
Background Assessing the impact of cannabis on cognitive and physical performance is imperative, especially in safety-sensitive environments. This study investigated the degree and duration of performance impairment after cannabis consumption. Methods Fourteen cannabis users were subjected to physical and cognitive testing before and after smoking cannabis. Tests included assessment of intoxication, vital signs, psychomotor abilities, and muscle function. Blood, urine and saliva were analyzed for Delta-9-tetrahydrocannabinol (THC) and Carboxy-THC at baseline, and 1-, 6-, and 12-hours post-consumption. Results Blood THC levels peaked significantly at 1 hour and declined by 6 hours (p < 0.001), whereas Carboxy-THC levels showed a less pronounced but consistent variation over time (p = 0.005). Urine Carboxy-THC levels displayed a non-significant similar trend (p = 0.068). Acute cannabis use significantly (p = 0.01 – p < 0.001) raised systolic blood pressure and heart rate, increased force variability, reduced rate of force development, and compromised balance and muscle endurance up to 12 hours post-consumption. Conclusions Acute cannabis consumption results in physical impairments, impacting essential functions required for safety-sensitive tasks. The sustained presence of Carboxy-THC indicates prolonged pharmacological effects and necessitates cautious policy-making for workplaces. Trial Registration This study was not registered as a clinical trial as the ClinicalTrials.gov indicates that the study must answer yes to all four questions on their checklist. Although, our study was interventional, it was not conducted in the US nor involved a new FDA investigational new drug application, and the cannabis was not manufactured or exported from the US. The focus of the study was on the recreational use of a single cannabis cigarette on subsequent physiological or work performance and safety measures over 12 hours.
... This suggests a direct carryover effect on daily activities. Similarly, primary studies have demonstrated an inconsistent application of the specificity principle across training and assessment [115,116]. In one study, the authors argued that the benefits of traditional resistance training for improving muscle strength have limited transfer to the performance of activities of daily living (ADLs) in the elderly population [116]. ...
Article
Full-text available
This article challenges the prevalent approach in exercise science for improving functional performance in older adults. It argues that contemporary exercise research and practice adhere to an outdated paradigm that undermines the principle of specificity in training and assessment. The author supports this central critique by examining fundamental issues including conceptual imprecision, paradigmatic limitations, and misapplications of core theories of motor learning. Additional evidence from exercise science literature demonstrates how these issues compromise the effectiveness of interventions by violating the specificity principle. To address these limitations, the author proposes a preliminary framework titled 'The Emergence of Skilled Mobility in Ageing' (ESMA), which aligns training and evaluation with individual task environment constraints. This framework recognises the critical role of adaptive variability and representative practice design in optimising coordination, skills, and mobility. The proposed preliminary framework has significant implications for interdisciplinary collaboration and knowledge translation through focused and ecologically valid assessments and interventions. Overall, this article identifies key gaps in the current exercise science paradigm for older adults and offers an integrated solution that promotes specificity and real-world functioning. Future research will focus on the development and validation of this framework.
... Furthermore, it connects upper and lower extremities via the abdominal fascial system, hence assuming not only a stabilizing but also a mobilizing function [73][74][75]. For such reasons, our AST protocol expressly focused on core recruitment and strengthening, also combined with upper and lower limb motion and unstable surface utilization [76][77][78], since it represents the fulcrum of the whole-body functional kinetic chain. Literature has repeatedly evidenced the importance of the core in optimizing force control and minimizing upper and lower body injuries, especially in overhead athletes [79,80]. ...
Article
Full-text available
Background and Objectives: Vision significantly contributes to postural control, balance, coordination, and body kinematics, thus deeply influencing everyday functionality. Sight-impaired subjects often show upper body anatomofunctional and kinetic chain alterations negatively impacting daily living efficiency and autonomy. The present study aimed to investigate and train, for the first time, upper body sensorimotor control in an Italian blind baseball team to boost global and segmental functionality while contemporarily prevent injuries. Materials and Methods: The whole team underwent a validated test battery using both quantitative traditional tools, such as goniometric active range of motion and muscular/functional tests, and an innovative biofeedback-based device, a Libra proprioceptive board. Consequently, a 6-week adapted training protocol was designed and leaded to improve sensorimotor control and, hence, counteract disability-related deficits and sport-specific overuse syndromes. Results: Statistically significant improvements were observed in all the investigated parameters. Noteworthy, an overall boost of global and segmental stability was detected through an orthostatic dynamic balance enhancement during the Y Balance test (p = 0.01) and trunk multiplanar control improvement on the Libra board (p = 0.01). Concurrently, the comparison of baseline vs. post-intervention outcomes revealed a consistent increase in upper body mobility (p < 0.05 for all the assessed districts), core recruitment (p = 0.01 for all the administered functional tests), and proprioceptive postural control (p = 0.01 for the Libra board validated test). Conclusions: Our findings suggest that a tailored sensorimotor training, conceived and led by an adapted physical activity kinesiologist, may effectively improve upper body functional prerequisites and global proprioceptive control, thus potentially promoting autonomy, quality of life, and physical activity/sport practice adherence in visually impaired individuals.
... Recent research has demonstrated that PT can have equivalent or even superior results than traditional resistance training in terms of enhancing athletes performance by enhancing their balance, power, agility, and strength. [16,17] For instance, it is found that six weeks of physical therapy dramatically increased the dynamic balance and knee proprioception of female badminton players, which ultimately helped to keep players from getting hurt. [18] Exercises performed on Swiss balls are nearly comparable to those performed with body weight, with the exception that they are slightly more difficult due to the unstable surface of the balls, which helps to increase the stability and strength of the muscles that stabilize the body. ...
... Core exercises provide unstable conditions that can stimulate proprioception by providing feedback for maintaining balance and sensing body position [32]. Instability induces rapid changes in muscle-tendon unit length, tension, and neuromuscular activity, which contribute to the ability to detect proprioception and respond reflexive activity accordingly [33]. Pilates exercises utilizing core muscles have been shown to enhance proprioception in healthy adults [34], while core stability training on unstable surfaces has been effective in improving proprioception in athletes with chronic ankle instability [35]. ...
Article
PURPOSE: This study aimed to validate the effect of core-based exercise on proprioception in individuals with neurological disorders through a systematic review and meta-analysis.METHODS: A systematic literature search was conducted using databases such as PubMed, Web of Science, and Scopus for studies published up to October 10, 2023. The search yielded 1,945 articles, with seven studies ultimately included for in-depth analysis. Meta-analysis was performed using Review Manager 5.4 software. Standardized mean differences (SMDs) were calculated using Hedges’ g value using both random-effects and fixed-effects models.RESULTS: The meta-analysis revealed that core-based exercise significantly improved joint position sense (SMD = -1.33; 95% confidence interval [CI] = -2.09 to -0.57; I²= 0%; p < .001) and kinesthesia (SMD = -0.33; 95% CI = -0.62 to -0.05; I²= 0%; p < .05) in individuals with neurological disorders. In a sub-analysis by the type of neurological disease, core-based exercises were beneficial only for stroke patients (SMD = -1.05; 95% CI = -2.07 to -0.03; I²= 58%; p < .05), but not for those with Parkinson’s disease or chorea. An analysis by the type of core exercise showed that core stability exercises had a significant benefit (SMD = -0.55; 95% CI = -0.97 to -0.14; I²= 0%; p < .001), whereas yoga exercises did not demonstrate a significant effect.CONCLUSIONS: In this study, core-based exercises positively improved proprioception in patients with neurological disorders, and were particularly effective in stroke patients. Among various types of core exercises, only core stability exercises had a positive effect on proprioception in patients with neurological disorders.
... However, it is interesting to note that in the present study, deep abdominal muscles, such as the transversus abdominis and internal oblique muscles 31,32 , which have been discussed as muscles related to trunk stability in many studies, did not appear to be related to motor control. The transversus abdominis and internal oblique muscles are considered to contribute to the overall stability of movement rather than direction-specific activity such as the rectus abdominis 33 . In addition, the cessation of trunk movement requires the overall activity of all muscles, not just a single muscle 34 . ...
Article
Full-text available
Objectives To verify the relationship between the indicators of components of lumbar motor control and determine the factors related to the indicators to each of these components. Methods Twenty-five healthy university students were included in the study. The lumbar spine and hip kinematic parameters of posterior/anterior pelvic tilt (mobility and smoothness), ball catching (reactivity), and forward/backward rocking (adaptive stability) were measured as indicators of lumbar motor control. Lumbar proprioception, trunk muscle strength, and lower trunk muscle thickness were also measured. Kinematic parameters of the lumbar spine and hip were measured using a small accelerometer. The data verified the relevance of indicators of lumbar motor control and the relationship with relevant factors. Results No significant correlations were found for most lumbar motor control indicators. Lumbar proprioception and rectus abdominis muscle thickness were identified as relevant indicators of lumbar motor control. Conclusions Each component of lumbar motor control is independent and must be evaluated for the component whose function is required. Additionally, some components of lumbar motor control are associated with lumbar proprioception and rectus abdominis muscle thickness; thus, evaluation of these components is necessary when evaluating lumbar motor control.
... Those who emphasized the importance of an unstable surface in resistance training concluded that greater instability increased neuromuscular stress (Anderson & Behm, 2005a;Anderson & Behm, 2005b;Behm & Anderson, 2006;Norwood et al., 2007). Besides, studies comparing the effects of surface stability in terms of the muscles responsible for exercise in the lower extremities reported different electromyographic activity (Hyong & Kang, 2013;Maior et al., 2009;McBride et al., 2006;McBride et al., 2010;Saeterbakken & Fimland, 2013 squat exercises with stable and unstable conditions, and they concluded that stable conditions showed the same or significantly higher value for VL muscle activity. ...
Article
Full-text available
In this study, it was aimed to compare the vastus medialis and vastus lateralis muscle activations during squat exercises performed on different surfaces. 14 males took part in this study. A ground surface is used as a stable surface, a gymnastics mat and a Bosu ball are used as an unstable surface. Participants performed 2 sets of squats on 3 surfaces and 10 repetitions of each set. Participants performed squat exercises with their own body weight. Muscle activation measurements were made from the vastus medialis and vastus lateralis muscles during the squat movement on each surface. A one-way repeated-measures analysis of variances was used for the statistical comparison of muscle activations between surfaces. As a result of statistical analysis, no significant differences were found in the vastus medialis and vastus lateralis muscle activations between surfaces (p>0.05). In conclusion, it was determined that the vastus medialis and vastus lateralis muscle activation in the squat movement was not affected by the stability of the surfaces.
Article
Context: Suspension training devices are becoming increasingly popular. Most studies analyzed the effectiveness according to diverse measures in patients with or without conditions at any age. The characteristics of suspension training are very specific and can increase instability and; therefore, enhance balance. The goal was to determine the effects of suspension training on balance by comparing it with instability training. Design: Two-arm, randomized trial. Methods: 44 young adults, aged 22.4 years old, with no musculoskeletal condition, took part. There were 2 interventions, suspension and instability training, designed with 12 sessions in 4 weeks. The primary outcome was the Y-Balance test. Other balance outcomes were the Emery and jumping sideways tests, and platform measures while standing. Results: Suspension and instability training were effective in enhancing balance in terms of the primary outcome, the Y-Balance test, with no between-group differences. Instability training enhanced the Emery test over suspension training (P = .018), but the latter was more effective in the jumping sideways test (P = .003). Neither of the training improved static balance measures. Conclusions: Training with suspension devices is effective in enhancing dynamic balance, with similar improvements to instability training. Importantly, the magnitude of change and the frequency of responders to intervention in terms of motor coordination and keeping balance in unstable conditions appear to be sensitive to the type of training.
Article
This study aimed to compare the effects of two elastic band 10-week training programmes on the athletic performance in adolescent female handball players. Participants aged 16.0 ± 0.5 years were randomly assigned to control (CNT, n = 12), standard elastic band (SEB, n = 12), or contrast elastic band (CEB, n = 12) programmes, each performed twice a week supplementing the regular training. The sprint (10 m and 20 m), modified Illinois change-of-direction test (COD), squat jump (SJ), countermovement jump (CMJ), standing long jump (SLJ), back extensor strength (BES), medicine ball throw (MBT), 1-RM bench press, 1-RM half squat, repeated sprint ability, and force-velocity (F-V) tests were measured before and after the intervention. Both CEB and SEB similarly improved sprint (p < 0.01 and p < 0.01) and COD (p < 0.001 and p < 0.01) when compared to CNT. Jumping performance improved significantly (SJ p < 0.01; CMJ p < 0.05) only in CEB, compared to CNT. Strength improved in both experimental groups (p < 0.01; ES: 0.73 < d < 1.59) compared to CNT, and there was a greater increase for CEB than SEB (p < 0.05) in the medicine ball throw (Table 3). Both CEB and SEB increased all RSA scores compared to CNT (p < 0.01; ES: 0.10 < d < 1.22), without significant difference between them. All F-V scores increased significantly in CEB and SEB compared to CNT (p < 0.01; ES: 0.45 < d < 2.47). In addition, CEB showed substantial gains in performance for PPabs, PPrel, and F0 (p < 0.001, p < 0.001 and p < 0.05, respectively) compared to SEB. Ten-week elastic band training conducted within the competitive season improved limb strength, power and F-V profile in female handball players, with a superior effect of the contrast elastic band training mode for upper-limb strength and F-V characteristics.
Article
Full-text available
We examined 4 shoulder muscles-the supraspina-tus, infraspinatus, the middle portion of the deltoid and the descending part of the trapezius-with electromyography (EMG) in abducted and flexed arm positions, in 9 healthy subjects. the subjects were asked to produce a static handgrip force of 30% and 50% of maximal voluntary contraction (MVC) in 8 different arm positions. in all positions, the subjects held a dynamometer in the hand. the myoelectric activity in the shoulder muscles with only the dynamometer in the hand was compared to the EMG activity when static contractions were added. There was an association between static handgrip and shoulder muscle activity, as revealed by EMG. the EMG activity increased in the supraspinatus muscle in humeral flexion from and above 60° and in 120° abduction. in the infraspinatus muscle, the changes were less; a significant increase, however, was noticed in flexion. in the deltoid muscle there was a tendency towards increased activity in positions lower than 90°, in the higher arm positions, the activity decreased. There was no significant alteration regarding the EMG activity of the trapezius. Our findings imply that high static handgrip force, particularly in elevated arm positions, increases the load on some shoulder muscles. the stabilizing muscles (the rotator cuff) were more influenced than the motor muscles by hand activity. Handgrip activity is important to evaluate while assessing shoulder load in manual work and in clinical evaluations of patients with shoulder pain.
Article
Full-text available
Strength gains have been attributed to neural adaptations such as alterations in recruitment, rate coding, synchronization of motor units, reflex potentiation, co-contraction of antagonists, and synergistic muscle activity. Although most training studies show increases in EMG, a few have shown increase in strength with no apparent changes in neural drive. This may highlight the importance of motor control and the reorganization of supraspinal inputs. High intensity concentric and eccentric contractions with arousal and imagery techniques merit further study in promoting optimal neural adaptations. Specificity of training mode, type of contraction, and angle and velocity have been documented. Most velocity specificity studies have emphasized movement rather than contraction speed, which may be the predominant factor. The high rate of force development achieved with ballistic contractions should serve as a template for power training. The extent of muscle hypertrophy is dependent upon protein degradation and synthesis, which may be enhanced through high intensity, high volume eccentric and concentric contractions. (C) 1995 National Strength and Conditioning Association
Article
The benzodiazepine receptor ligand iomazenil was labelled with carbon-11 to allow a direct positron emission tomography/single-photon emission tomography (PET/SPET) comparison with the well-known iodine-123 labelled compound. Imaging showed the same regional distribution for both modalities. Blood sample activity was corrected for metabolites by extraction with chloroform and high-performance liquid chromatographic analysis. Metabolism is very fast: 5 min after application more than 85% of the plasma activity is present as hydrophilic metabolites. Kinetic methods were used to obtain regional estimates of transport rate constants and receptor concentrations. A three-compartment model was employed which gave transport rate constants for brain uptake (K 1) and the distribution volume for the specifically receptor bound compartment (DV s).K 1 varied from 0.32 to 0.50 ml/min per gram for the cortical regions, cerebellum, thalamus and striatum for PET and SPET. MeanDV s-PET andDV s-SPET values were, respectively, 235 and 315 ml/g for the occipital cortex, 113 and 152 ml/g for the cerebellum, 72 and 113 ml/g for the thalamus, 53 and 103 ml/g for the striatum, and 32 and 31 ml/g for the pons. These values correlated very well individually. The coefficient of variation of the SPET parameters was quite comparable to that of the PET parameters, especially after 180 min (PET 90 min) study duration. Thus quantitative benzodiazepine receptor information can be obtained from dynamic SPET imaging in the same way as with PET.
Article
The experiment that was carried out consisted of subjects pushing an external object (a heavy pendulum) using stable and unstable handles of increasing mobility. Using this protocol it was possible to distinguish between the motor and stabilising functions of the muscles of the upper extremity. The motor functions were realised by the extensors of the upper extremity, whereas stabilising functions were effected by the muscles spanning the wrist joint. The experiment involved synchronised measurements of the electromyographic (EMG) activity of the muscles in question together with several mechanical quantities revealed against the external object: force, velocity and power. As a result, the instantaneous and global EMG contributions of the extensor and stabilising muscles were determined. It was found that it is the equilibrium state of the object being set in motion and not its mobility (expressed in terms of the number of degrees of freedom) that influences the forces produced by individual muscles. We also suggest that the realisation of stabilising functions by skeletal muscles is a necessary condition of performing any voluntary and co-ordinated movement.
Article
Objectives: To assess the paraspinal and abdominal muscle activities during different therapeutic exercises and to study how load increment produced by varying limb movements and trunk positions could affect these muscle activities. Design: A cross-sectional study comparing muscle activities between men and women. Setting: Rehabilitation clinic in university hospital. Participants: Twenty-four healthy volunteers (14 women, 10 men) aged 21 to 39 years. Interventions: Subjects performed 16 different therapeutic exercises commonly used to treat low back pain. Main outcome measures: Surface electromyography was recorded from the paraspinal (T9, L5) and abdominal (rectus abdominis, obliquus externus) muscles during these exercises. Average electromyographic amplitudes obtained during the exercises were normalized to the amplitude in maximal voluntary contraction (% MVC) to produce interindividually comparable muscle activity assessments. Results: Mean average normalized electromyographic amplitudes (% MVC) of the exercises were below 50% MVC. At L5 level, the multifidus muscle activities were significantly higher (p <.05) in women than in men, whereas no significant difference was found at T9 level. Similarly, rectus abdominis and obliquus externus activities were significantly higher (p <.001, p <.05) in women than in men. Load increment in hands or unbalanced trunk and limb movements produced higher paraspinal and abdominal muscle activities (p <.05). Conclusions: Simple therapeutic exercises are effective in activating both abdominal and paraspinal muscles. By changing limb and trunk positions or unbalancing trunk movements, it is possible to increase trunk muscle activities. Women were better able to activate their stabilizing trunk muscles than men; but it is also possible that men, having a much higher degree of strength on maximal contraction, only need to activate a smaller amount of that maximum to perform a similar activity.
Article
This study calculated IEMG values during the ascent and descent phases of the bench press and compared the values between lifts performed with free weights versus a guided weight machine. In Phase 1 of the study the 1-RM on each mode was determined for each subject. In Phase 2, EMG data were collected from five muscles of the upper extremity while each subject completed five trials at 80% of 1-RM and five trials at 60% of 1-RM for each mode. Linear envelopes were created from the EMG data of each trial, and IEMG values were calculated during the descent and ascent phases of each trial. Planned comparisons were used to compare mean IEMG values between the two loads within the same mode, and between the two modes at both the 60% and 80% loads. Results suggested greater muscle activity during the free-weight bench press, especially at the 60% 1-RM load, although there were notable differences among the patterns of individual subjects.
Article
Muscle size and strength decrease with aging, and resultant muscle weakness has been implicated in increased risk of falls in older adults, falls which have large economic and functional costs. Most studies examining the effect of exercise on risk of failing have utilized multifaceted exercise interventions. The purpose of this randomized, controlled study was to determine if an 8-week, 3-day per week intense (75% of 1 repetition maximum) strength training program, in the absence of aerobic or flexibility training, could improve postural stability in 24 subjects aged 61-87 (Mean = 72, SD = 6.3). Eleven strength training-naive subjects performed two sets of 10 repetitions for six different lower body exercises. Post-intervention strength was significantly better (p <.017) in all training subjects across all exercises, and no injuries were reported as a result of either training or 1RM testing. After controlling for pre-intervention differences, repeated measure ANCOVAS found a significant difference between experimental and non-intervention control subjects for post-intervention maximal walking speed (F(1, 19) = 5.03, p < .05). There were no significant between-group differences for 1-leg blind balance time or 5-repetition sit-to-stand performance (F(1,19) =.082; F(1,19) =.068, respectively, p >.05). These findings suggest that strength training alone does not enhance standing balance or sit-to-stand performance in active, community-living older adults, but may improve maximal walking speed. The data also reinforce the notion that intense strength training is a safe and effective way to increase muscle strength.