What is currently known about hypotonia, motor skill development, and physical activity in Down syndrome
Mark Latash, Louise Wood and Dale Ulrich
A great deal of variability exists in the Down syndrome population in terms of their motor control, coordination, and skill. Virtually all papers on motor control, motor development, and motor learning in Down syndrome mention low muscle tone or hypotonia as a major contributor to the typical differences between movements performed by individuals with and without Down syndrome. Our paper makes an effort to discuss what is currently known about hypotonia, motor skill development, and physical activity in Down syndrome. There is a critical need for more objective measures of muscle tone or stiffness and the design and testing of interdisciplinary interventions to maximise physical activity, health, and community participation in the Down syndrome population.
Considerable variability exists among individuals with Down
syndrome with regard to the degree of disability and the specific features
affected. Greater joint range of motion, presumably attributable to ligamentous
delayed development of postural reactions and myelination,
low muscle tone,
and congenital heart defects,
have been hypothesised as major contributors to delayed motor skill development.
In this paper, we will discuss potential causes for hypotonia in individuals
with Down syndrome, why the development of motor skills are important in young
children, adolescents, and adults with Down syndrome, what is known about
physical activity levels in Down syndrome and the importance to health and
movement skill development. Persons interested in a good overview of what is
generally known about motor development and Down syndrome are encouraged to
access the work by Sacks and Buckley, Palisano et al., Jobling and Mon-Williams,
Block, and Henderson[5-9].
Potential causes for hypotonia in Down syndrome
Virtually all papers on motor control, motor development, and
motor learning in Down syndrome mention
low muscle tone
as a major contributor to the typical differences between movements performed by
persons with and without Down syndrome[3,9-12].
is a frequently used clinical term that has no clear definition, no unambiguous
interpretation in terms of possible mechanisms, and no universally accepted
method of measurement[3,13,14].
This situation has introduced a lot of confusion into the literature; for
persons with Down syndrome it was summarised by Greg Anson:
"In sum, the role of hypotonia in accounting for movement
disorders in individuals with Down syndrome can no longer be considered a
default explanation when all alternatives fail[15:
Nevertheless, it is impossible to ignore the fact that there
is a phenomenon or a complex of phenomena that allow practitioners to
distinguish a person with â€˜normal toneâ€™ from a person with â€˜high toneâ€™ (for
example, in spasticity, reviewed in Katz and Rymer),
and from a person with â€˜low toneâ€™ (for example, in Down syndrome, for a review
see ref 12).
The purpose of this paper is not to argue about the terminology but to try to
understand what mechanisms could bring about a subjective perception in an
examiner that leads to claiming
hypotonia in persons with Down syndrome. We believe
that a good first step would be to introduce an operational definition of
â€˜hypotoniaâ€™ that follows the most common practice of its assessment. There are
other methods of measuring â€˜toneâ€™, for example studies of tissue deformation to
a light pressing or pinching
[3,17] and of joint mechanical reactions to random
However, to avoid confusion, let us accept the one that seems to be most
An examiner moves a joint of a person smoothly and slowly,
while the person is instructed to relax and not to resist the motion. The
examiner compares the feeling of resistance to his or her â€˜internal gaugeâ€™ based
on previous experience â€“ what he or she associates with being â€˜normalâ€™ â€“ and
lower than expected resistance is called â€˜hypotoniaâ€™.
This operational definition, although suboptimal (since it
relies on a subjective feeling of the examiner), allows to identify a few
potential contributors to muscle
tone. These contributors reflect a number of factors
that may affect the resistance an examiner feels when he or she tries to move a
limb segment of another person.
1) Viscoelastic properties of tendons and ligaments and inertia
of body segments
Assuming that a person is relaxed completely, and during the
examination muscle activation levels show no deviations from zero, joint
resistance will be defined primarily by the mechanics of peripheral tissues. In
a first approximation, resistance to an external motion gets contribution from
inertia, elasticity (resistance to stretch), and damping (resistance to
velocity). In particular, human tendons and ligaments provide for a non-linear
viscoelastic behaviour of passive joints, while relaxed muscle fibres show
relatively low resistance to stretch[18,19].
If joint motion is performed quickly, the inertial resistance also cannot be
The following factors can potentially lead to lower
resistance to externally applied motion in persons with Down syndrome. Laxity of
ligaments, lower inertia of the body segments (in particular, they are shorter),
and more compliant tendons. The first two factors may be viewed as
The shorter limbs of persons with Down syndrome allow to expect significantly
smaller moment of inertia. In fact, a 20% shorter limb segment (assuming
proportional scaling of all its dimensions) provides less than half of the
inertial resistance to motion given the same angular acceleration.
2) Ability to relax muscles crossing the joint
This ability cannot be taken for granted. In some cases, such
as spasticity, people cannot relax muscles at certain joint configurations,
while under emotional stress, or when their body parts move (reviewed in Dietz).
Even a typical, healthy person may need explanation and time to be able to relax
when his/her limb segments are manipulated by another person. It is common
knowledge that some people are able to relax â€˜completelyâ€™ during massage or
other manipulations while others cannot or, at least, require reminders and time
It is theoretically possible that persons with Down syndrome
can relax quicker and more completely than persons without Down syndrome. If so,
this contributor to hypotonia
reflects their BETTER control of muscles! Unfortunately, recording minimal
muscle activation during incomplete relaxation is very difficult. However, this
is not impossible, and we would not be surprised if residual muscle activation
levels prove to be higher in persons without Down syndrome as compared to those
with Down syndrome.
Typically, researchers assume that participants in
experimental studies and clinical examinations do not react voluntarily unless
they are instructed to do so. However, persons without Down syndrome may show a
creeping change in their â€˜relaxedâ€™ muscles towards higher activation (or closer
to the threshold of activation) with joint motion, particularly if the test
lasts for some time. Persons with Down syndrome typically show less initiative
and may be more compliant with the instruction to relax and stay relaxed over
the examination time.
3) Ability to avoid or minimise involuntary muscle activation
during joint motion
We assume that the motion produced by the examiner is smooth
and not very fast. As such, it is not expected to produce monosynaptic reflexes
or long-latency pre-programmed reactions (also known as M2-3,
reviewed in Chan and Kearney;
McKinley et al.)
in the stretched muscles. Involuntary muscle activation during not very quick
joint motion can be seen if the threshold for muscle activation is reached
during the motion (Figure 1).
Muscles with zero activation can be deeply relaxed (their activation threshold
is very far, possibly beyond the anatomical range of joint motion) or
superficially relaxed (their activation threshold is close and can be easily
reached if the muscle is stretched). Note that a similar explanation has been
offered for involuntary muscle activation in spasticity[25,26].
If joint motion leads to muscle activation, the viscoelastic properties of
muscle fibres take over the contribution of the tendons and ligaments to joint
resistance to motion and define this resistance[27,28,29].
Figure 1 |
Two force-length dependences are shown on the force-length (F-L)
plane. In the initial position (the black dot), muscle length is shorter than
the threshold for muscle activation corresponding to either curve. The muscle is
completely relaxed. A passive motion stretching the muscle (the arrow) may lead
to different levels of muscle activation and different active muscle forces
depending on the actual location of the force-length muscle relation. Curve-1
corresponds to a "less relaxed" muscle as compared to curve-2.
These considerations allow us to offer the following
hypothesis: Persons without Down syndrome typically are ready to produce
corrective actions in situations of unexpected events in the environment. Hence,
even when they seemingly relax muscles completely (there is no visible
electrical muscle activity), muscle activation thresholds are never too far and
can be easily reached with passive joint motion (as illustrated by curve-1 in
Persons with Down syndrome are known for their slower reactions to virtually any
stimuli. This may be partly due to their deeper relaxation, such that it takes
more time to bring muscles to activation thresholds (illustrated by curve-2 in
The deeper relaxation is reflected in smaller active muscle force (and smaller
muscle activation) during passive joint motion (compare the final points P1 and
P2 in Figure 1)
and, respectively, to lower resistance to joint motion.
4) Effects of reactive muscle activation on joint resistance to
There are two basic types of muscle reaction to joint motion,
reciprocal and co-activation. The reciprocal pattern leads to activation of the
stretched muscle without activating the shortened one.
illustrates muscle torque-angle characteristics for a pair of muscles opposing
each other (an agonist-antagonist pair). Note that the antagonist muscle
produces negative torque. Both muscles are relaxed in the initial joint
position, that is the active torque produced by each muscle is zero. If in
response to joint motion the characteristics move in the same direction
(reciprocal shift, see ref 30)
to counteract the imposed action, the stretched muscle becomes likely to show
non-zero activation, while the shortened muscle remains quiescent. An
alternative, co-activation pattern is illustrated in
Figure 2B. Joint
motion leads to shifts of the two torque-angle characteristics in opposite
directions such that both muscles may be expected to show a non-zero activation
level. Note that if one assumes similar magnitudes of the shifts of the
characteristics, the net resistance in the case of the reciprocal pattern (net
torque, TNET) is expected to be higher than in the co-activation
Figure 2 | Originally, both muscles acting at a joint are relaxed (black
dot). In response to passive motion, in panel A the muscle torque-angle curves
shift in the same angular direction (recipricol shift). In panel B, the two
curves shift in opposite directions (co-activation shift). As a result, the net
active joint torque is higher in A than in B (open circles).
Persons with Down syndrome are known to show co-activation
patterns in many tests where persons without Down syndrome show reciprocal
patterns. Such patterns have been shown during voluntary movements, during
anticipatory postural adjustments, and during reactions to perturbations of limb
joints and of vertical posture[31,32,33].
suggests that reciprocal activation of the agonist-antagonist muscle pair is
expected to create a larger resistance to motion as compared to that produced by
a co-activation pattern. So, somewhat counter-intuitively, preference for
co-activation patterns in Down syndrome may be a contributor to hypotonia!
Another factor that may distinguish between persons with and
without Down syndrome is the slope of the relation between muscle length and
active muscle force. However, available data suggest that the slope of muscle
and joint characteristics is not changed in persons with Down syndrome[34,35].
This conclusion is also supported by a study of postural responses to unexpected
platform displacements, which led the authors to conclude that Down syndrome is
associated with a basically intact segmental spinal apparatus.
Consideration of potential contributors to muscle tone during
The preceding discussion of potential contributors to muscle
tone during passive limb movements suggest several limitations of previous
research which has largely relied on the subjective assessment of resistance to
an external motion, including failure to:
i) document joint range of motion and the velocity of
limb movement. This neglects the rate and deformation dependency of muscle
and connective tissue responses,
ii) standardise the position of force
application/resistance measurement in relation to limb segment length or the
use of anthropometric measurements to aid interpretation of resistance
iii) use EMG to monitor involuntary muscle activation or
level of voluntary reciprocal/co-activation.
In addition, ratings of tonus may be influenced by perception
of muscle strength and joint range of motion. Sanger noted that muscle weakness
may coexist with hypotonia
â€“ but muscle weakness may be the biggest contributor to the observed patterns of
everyday movements. Unsurprisingly therefore, typical subjective clinical
assessments demonstrate poor ability to discriminate tone at the lower ends of
weak inter-observer agreement and inconsistencies in the characterisation of
tone in infants.
Reliable, objective methods are required to substantiate hypotonia in Down
syndrome and to subsequently examine the relation between tone and motor
development. It is also proposed that definitions of hypotonia differentiate
between passive properties of a joint (inertia and viscoelastic soft tissue
properties), intrinsic muscle activation/co-ordination patterns and involuntary
This will aid the understanding of the neurophysiological basis of hypotonia.
Assessment of musculotendinous properties
The ability to assess and compare connective tissue
properties of individuals with and without Down syndrome will enable further
insight into key determinants of motor development. It may also enable the
development of more sensitive methods of clinical assessment. Relatively little
is known about the development of muscle elastic development with age and
maturation in typically developing children.
This may reflect the relatively recent development of methods allowing
noninvasive in vivo measurements.
To develop a more objective measure of â€˜hypotoniaâ€™ in
children with Down syndrome, it is useful to revisit our initial definition
regarding current clinical assessment: An examiner moves a joint of a person
smoothly and slowly, while the person is instructed to relax and not to resist
the motion. The examiner compares the feeling of resistance to his or her
â€˜internal gaugeâ€™ based on previous experience â€“ what he or she associated with
being â€˜normalâ€™ â€“ and lower than expected resistance is called â€˜hypotoniaâ€™. This
reflects the perception of â€˜passive resistance to motionâ€™ â€“ resistance observed
when the relaxed musculotendinous structures are stretched throughout a
specified joint range of motion. It may be considered to represent a simplified
measure of â€˜stiffnessâ€™ which is the ratio of stress (force per unit
cross-sectional area of the material) to strain (change in length relative to
original length) â€“ characterising the deformation of a material under load. Due
to the difficulty of measuring the cross-sectional area and fibre length of
biological tissues in vivo, the ratio of the force or torque resisting motion to
joint angular displacement (assessed using dynamometry and EMG) can be used as a
simpler representation of stiffness.
Considering the factors that are known to influence muscle
tone/stiffness (inertia and viscoelastic soft tissue properties, intrinsic
muscle activation/co-ordination patterns and involuntary activation, the
examination of stiffness in infants is complicated by ethical issues and subject
compliance. Maximal muscle actions cannot be electrically evoked prior to
perturbation of the joint to separate the contribution from reflexive and
non-reflexive stiffness components. Neither can the infants be instructed to
voluntarily maintain a fixed torque during perturbation. Therefore, as a start
point, it may be prudent to objectively examine the passive stiffness of muscle
groups (confirmed by EMG) during joint movement. Eliminating intrinsic muscle
and reflex activation contributions, the objective measurement of passive
resistance to motion will allow muscle and connective tissue material properties
during stretch to be examined. As previously stated this would require the
degree and velocity of stretch to be controlled. Surprisingly this does not
appear to have been studied in children with Down syndrome, even though
protocols for assessing passive resistance to motion have been described in the
An extension of the objective assessment of passive
resistance to motion in children would be to estimate muscle/tendon
cross-sectional area and fibre length data in vivo to allow more reliable
stiffness values to be derived. Techniques for assessing contractile and/or
tendon length and muscle cross-sectional area in vivo include: sonomicrometry,
magnetic resonance imaging (real-time and cine phase contrast), X-ray scanning
and ultrasound .
Of these methods, ultrasound has gained popularity due to being non-invasive,
more affordable, portable and may be less time consuming;
its ability to be used during passive resistance to motion assessment
(measurements are not constrained to the confines of a scanner), and due to
improvements in musculotendinous visualisation and tracking.
Therefore in addition to passive resistance to motion tests, the measurement of
musculotendinous properties and response to stretch would aid the interpretation
of variation within and between individuals (since differences in muscle/tendon
cross-sectional area and elongation during stretch can be considered). These
analyses will enable â€˜hypotoniaâ€™ to be examined more reliably, and quantitative
data will assist examination of links to motor performance making intervention
strategies more reasonable to test.
Tone and motor skill performance
Muscle structural properties and neural activation influence
the development of mature postural reactions and movement performance[2,46,47].
A critical level of musculotendinous stiffness/tone is necessary for contractile
forces to be transmitted to the skeleton.
The rate of force or torque development (indicative of the ability to perform
explosive muscle actions) has also been correlated with in vivo estimates of
connective tissue stiffness.
Despite this research, further studies are required to examine the role of
tone/stiffness in the motor development of children with Down syndrome. Aside
from the consideration of how to objectively assess muscle tone, methods of
assessing skill performance should also be briefly evaluated.
The walking development of infants with Down syndrome has
frequently been compared to typically developing infants to aid understanding of
motor delay. Sutherland et al. identified five determinants of mature gait:
duration of single limb stance, walking velocity, cadence, step length and ratio
of pelvic span to ankle spread.
Step length/limb length was also suggested to be an important marker of
neuromuscular maturation. Several kinematic differences between individuals with
and without Down syndrome have been noted which may contribute to the delayed
development of walking in children with Down syndrome. Rast and Harris noted
less ability to control anti-gravity movements of the lower extremity and
difficulties in adjusting head position in space in individuals with Down
Pelvic and hip instability, particularly excessive degrees of thigh abduction
have also been documented.
This may limit stepping ability, since the position of the hip is important for
load reduction at the end of stance and for swing initiation.
Also reduced plantarflexion moment of force and power generation in 8-36 year
old individuals with Down syndrome have been found suggesting â€˜hypofunctioningâ€™
of the ankle.
This would limit step length and possibly lead to a relative prolongation of the
stance phase of the gait cycle. These kinematic and kinetic differences may
suggest deficits in the strength and postural control (which may or may not be
influenced by muscle tone) required for the demonstration of mature gait
It is important to emphasise that few studies have actually
quantified (using biomechanical analyses), limb kinematics and/or kinetics
during walking development in Down syndrome. Typically developing children
demonstrate a wider base of support, reduced stride length and average walking
speed, a relatively flat-footed foot contact, minimal knee flexion during the
stance phase, externally rotated lower limbs during the swing phase and a lack
or reciprocal arm swing compared to adult gait patterns.
However Ganley and Powers recently noted that the actual differences between
child and adult gait, and the age at which children achieve a mature adult-like
gait are yet to be described.
This may reflect failure to consider factors controlling the acquisition of gait
(and therefore intra-/inter-individual variability) during data analysis. Thus
comparison of the development of gait in children with Down syndrome to
â€˜typicallyâ€™ developing children is difficult. Anthropometric characteristics
(body size, limb proportions) may contribute to the explanation of gait
variation in children and adults. Ganley and Powers compared gait sagittal plane
kinematics and kinetics of 7 year old (typically developing) children to adults
using age-specific anthropometric data (collected using dual X-ray
Joint kinematics did not significantly differ at the hip, knee or ankle between
the children or adults, however peak plantarflexor moments of force and peak
power absorption and generation were significantly lower at the ankle. It is
interesting to note that Cionni et al. interpreted the reduced plantarflexion
moments of force and power in 8-36 year old individuals with Down syndrome as
suggesting â€˜hypofunctioningâ€™ of the ankle
â€“ even though (according to Ganley and Powers)
this may reflect typical gait development in children. In addition, despite the
wide age range in the study by Cionni et al., only 17 participants with Down
syndrome were examined. There is a need to consider anthropometry when comparing
gait characteristics (particularly given the recognised differences between
children and adults with Down syndrome and typically developing children and
adults). Further biomechanical studies are warranted to enable atypical gait to
be differentiated in individuals with Down syndrome and subsequently the
identification of contributing factors.
The previous discussion of walking development in children
highlights other limitations of Down syndrome motor development research. The
majority of studies document the age at which specific motor milestones are
achieved, as opposed to the actual process of achieving these milestones. As in
walking, it is important to identify whether motor development is simply delayed
(with typical movement patterns displayed), or whether the movement patterns
used to achieve the milestone are atypical.
One of the most widely used scales to assess infant motor development â€“ the
Bayley scales of infant development, only enables a pass/fail distinction,
without judgement of the kinematics and kinetics of performance.
In summary, there is a need to re-examine hypotonia in
infants with Down syndrome and the proposed relationship to motor delay and
impairment. This requires more objective assessments to be undertaken. It is
proposed that future studies should explore protocols based on dynamometry (for
the measurement of passive resistance to motion) along with ultrasound
techniques. More sophisticated biomechanical analyses are also needed to assess
childrenâ€™s motor development adjusting for inter-individual differences in
To summarise, the following hypotheses on hypotonia in Down
syndrome may be offered:
H1: Tone does not significantly differ between
individuals with Down syndrome and typically developing individuals.
H2: Individuals with Down syndrome have more compliant
tendons and ligaments and lower inertia of limb segments.
H3: Individuals with Down syndrome have a better ability
to relax muscles completely and stay relaxed over the examination period
compared to persons without Down syndrome.
H4: Individuals with Down syndrome display deeper muscle
relaxation (the muscles are farther away from muscle activation thresholds)
compared to persons without Down syndrome.
H5: Individuals with Down syndrome demonstrate a
preference for co-activation patterns in contrast to reciprocal activation
patterns displayed by persons without Down syndrome.
What can be done to study these hypotheses:
H1: This hypothesis cannot be rejected until more
objective assessments of â€˜toneâ€™ or stiffness (considering confounding
factors) are implemented.
H2: Laxity of ligaments and lower inertia of body
segments may be viewed as proven. Studies should record appropriate
anthropometric measurements to aid explanation of variation in
musculotendinous and performance characteristics. Ultrasound techniques can
be used to assess the relative stiffness of muscle and tendon structures.
The question of how much the mechanical characteristics of peripheral
structures in persons with Down syndrome contribute to hypotonia can then be
addressed. This requires quantitative analysis of the other hypotheses.
H3: This hypothesis is likely to be very hard to study
because its testing requires reliable recording and quantitative analysis of
very small electromyographic (EMG) signals. Such a study may require using
arrays of EMG electrodes to be able to pick up small signals in any portion
of the studied muscles.
H4: Can be studied with controlled joint motion
(different amplitudes and velocities) under an instruction "relax the joint
and forget about it". Another approach would be to apply a controlled
mechanical perturbation (slow and smooth!) from a state when both muscles
show minimal, non-zero voluntary activation, for example 2% of maximal EMG
signal. Such an approach would also test the slope of the force-length
relation for the muscles.
H5: The hypothesis on the preference of co-activation
patterns in Down syndrome may be viewed as partly proven. It may be further
studied using controlled externally imposed cyclic joint motion.
Development of functional locomotor behaviours in infants and
children with Down syndrome
Acquiring the ability to locomote is important to infants
because of the impact on cognitive and social/emotional skills, as well as for
the more obvious relevance to subsequent motor skill development. At the
cognitive level, researchers have demonstrated that for typically developing
infants, experience with locomotion accounts for the onset of a broad array of
psychological skills. They include: the onset of wariness of heights, the
concept of object permanence (that objects hidden from sight may still exist), a
shift from self-centred to landmark-based spatial coding strategies, the ability
to follow the pointing gestures and gaze of another person, aspects of social
referencing, and detour reaching[57-61].
These data suggest that infants learn more about spatial cognition and the world
around them as they become able to locomote independently and can actively
explore their environment than through passive observation, i.e., being held or
carried through space. Rosenbloom further suggests that not only is locomotion
important but the quality of movement also effects subsequent development.
He proposes that inefficient locomotion may inhibit development by limiting the
attention and energy infants can focus on exploring stimuli in their
environment. Acquiring stable motor skills may be especially important for the
cognitive development of infants with Down syndrome. In our society delays in
motor development are often tacitly equated with delays in cognitive
development. Such assumptions may foster lower expectations from caregivers and
thus exacerbate their inherent delays.
The onset of the ability to walk alone represents an
important milestone for both infants and their parents, for social and emotional
reasons. Clinicians have described the onset of walking as a time of elation,
exhilaration, and delight, as well as of affective reorganisation and wilful
Parents of infants with Down syndrome report that walking is one of the goals
they value most for their young children. Family and friends repeatedly ask them
if their child has yet begun to walk and talk, a disconcerting question, as the
delays become longer. These are behaviours that are apparently universally
accepted as important. When infants finally walk on there own parents are
relieved and reassured by this quite tangible evidence that progress is indeed
being made. Jones, Liggon and Biringen documented that, following walking onset,
typically developing infants demonstrated greater independence (moved away from
mother more frequently than when they could only crawl) and showed an increase
in positive affect during play.
Interestingly, parents in the Jones et al. study indicated that they did not
notice the impact on their childrenâ€™s affect but consistently observed that
their child was more independent and physically active. For parents of children
with Down syndrome the importance of their childâ€™s increasing independence was
illustrated in a study conducted by Sloper and colleagues.
They studied factors that impacted on the stress levels and satisfaction with
life of 123 families of children with Down syndrome. For mothers, the primary
caregivers, stress level was strongly related to their childâ€™s self-sufficiency.
When children with a disability can walk alone, handling and physically caring
for them becomes easier for their parents. Treatments are therefore recommended
to start early so that the child may achieve optimal development.
In the motor domain, stable and efficient locomotor skills
form the foundation for developing more complex motor skills. Children use these
skills to interact with other children in games and activities. In school and
neighbourhood settings, children with poor motor skills are often excluded from,
or, choose to avoid physical activity. A longitudinal study of children with
Down syndrome from ages 1 month through to 6 years who had been enrolled in
early intervention programmes in Canada was conducted for the purpose of
developing motor growth curves.
Based on the results of the growth curves, the researchers concluded that
children with Down syndrome require considerably more time to acquire early
motor behaviours. For example, they predicted that at 24 months of age only 40%
of the children with Down syndrome would demonstrate the ability to walk across
the room and at 5 years of age only 45% would display the ability to run.
Anecdotal observations of children with Down syndrome suggest
that they tend to fall more often than their typically developing age peers
although no systematic study has verified these informal observations. A recent
study by Virji-Babul and Brown sheds some light on the issue of walking and
negotiating obstacles in children with Down syndrome.
Their findings suggest that children with Down syndrome have adopted one
strategy of negotiating obstacles at different heights and they do not appear to
use anticipatory adjustments as they are approaching the elevated obstacle like
typically developing walkers. The strategy used is to walk up to the obstacle
and stop and then extract the necessary information needed to step over the
obstacle safely. Their unwillingness to explore alternative strategies in this
functional task is in line with their primary goal of remaining safe as they
move in their environment
and their inability to use advance visual information as they move. Based on the
accumulation of research on the acquisition of early motor behaviours in Down
syndrome, one has to conclude that researchers and clinicians have not been
successful in meaningfully reducing the delay in onset of critical locomotor
behaviours and improving performance.
One intervention approach, treadmill training, has
consistently demonstrated positive outcomes in reducing the age of onset of many
Treadmill training of infants with Down syndrome is founded on the theory of
neuronal group selection (NGS)[71,72]
and principles of dynamic systems theory (DST)
applied to motor and cognitive development[20,73,74].
Being supported on a small infant sized treadmill by the parent (see
long before independent walking emerges, affords the infant with skill specific
practice using the alternating stepping pattern employed later in independent
walking. It was hypothesised that the experience resulting from stepping
practice over a longitudinal period strengthens and stabilises the synaptic
connections among motor neurons (neuronal groups) that drive the stepping
pattern. By providing the infant with frequent opportunities implemented in the
home to explore multiple leg coordination patterns in an upright posture,
promotes earlier selection of alternation as the preferred leg coordination
pattern. The treadmill stepping practice also advances critical subsystems
needed to walk: leg extensor strength and postural control.
Figure 3 | Mother implementing treadmill training
Treadmill training increases leg strength needed to support
their body weight during walking, and promotes specific postural control
mechanisms that are needed to maintain upright balance as the infant transfers
their weight from one leg to the other. The treadmill intervention initiated by
10-11 months of age takes advantage of a period of maximum neural plasticity and
meets Latashâ€™s recommendation of encouraging the infant with Down syndrome to
engage in early exploratory activity to facilitate the discovery of general
rules of motor coordination.
The results of two randomised intervention studies employing
the treadmill intervention as a supplement to physical therapy with infants who
have Down syndrome have clearly demonstrated that the intervention significantly
increases alternating stepping and reduces the age of onset of independent
walking and other pre-walking locomotor behaviours. The intervention has not
produced obvious harmful effects and may have additional positive outcomes
related to gait and physical activity[65,70].
More interventions, based on principles on NGS and DST, are needed for important
functional movement behaviours for children with Down syndrome and other
Physical activity and learning functional early movements
Physical activity and movement in children with and without
Down syndrome is a critical facilitator of learning.
As infants and children move they learn about the changing properties of their
own systems (e.g., limb lengths, muscle strength, postural control) and their
Neural solutions to movement problems encountered must be discovered as the
young child moves within his/her changing environment. Very limited research has
been conducted on physical activity as it relates to learning of functional
skills in children with and without Down syndrome. The common view based on
parent and professional reports is that young children with Down syndrome are
less active than their age peers without Down syndrome[75,76,77].
Based in part on these anecdotal reports, Henderson hypothesised that children
with Down syndrome have "a self-perpetuating form of sensory-motor deprivation
sparked off by an inbuilt passivity and disinclination to move"
[75:p.74]. If this hypothesis is true, it would help
to explain why infants and young children with Down syndrome experience
significant delays in acquiring early movement skills. Limited research has been
published to test this hypothesis. Ulrich and Ulrich compared the spontaneous
leg movements of infants with Down syndrome and two groups of typically
developing infants matched for chronological age and motor age.
Their results suggest that the frequency of leg movements were not different
between the three groups. These data suggest that poor motor skill development,
over time, is more likely responsible for low levels of physical activity
demonstrated later in life than is an inherent disposition toward inactivity.
Early interventions that promote the development of efficient functional motor
skills may, therefore, have a positive impact on multiple domains during infancy
and may also create a solid foundation for future success in movement settings.
In the Ulrich and Ulrich study, they did report that the infants with Down
syndrome produced significantly fewer complex patterned leg movements in the
form of kicks. In the three infant groups, infants who produced more kicks also
walked earlier. The explanation provided for the relationship between kicking
and age of walking relates to Edelmanâ€™s model[71,78]
which suggests that infantsâ€™ self generated kicks belong to the same category of
behaviours as the leg movements used to walk (hip, knee, and ankle flexions and
extensions). The flexion and extensions used in walking are similar to what is
seen in kicking. Given that the overall frequency of leg activity was not
different between the three groups, it casts doubt on the inherent inactivity
hypothesis. It is hypothesised that inactivity may be a learned or adaptive
pattern of behaviour that emerges with age.
McKay and Angulo-Barroso conducted a longitudinal study of
the spontaneous leg activity of infants with and without Down syndrome from
three to six months of age.
They placed an activity monitor on the right ankle of each infant for a period
of 48 hours. Their findings suggest that infants with Down syndrome spend a
greater duration of time throughout the day in low intensity leg activity. They
also reported a significant relationship between low intensity leg movement and
the age of onset of walking. The lower intensity activity might be attributable
to the muscle properties and slowness of movement discussed in the first section
of this paper.
Figure 4 | Inexpensive Kick Start Gym
A small longitudinal intervention study was conducted to test
if it was possible to increase kicking in 4-6 month old infants with Down
syndrome and, if so, what the effects would be on age of walking onset.
In this randomised study, infants with Down syndrome were given a Kick Start Gym
(see Figure 4)
or a Tummy Time Gym and the protocol required parents to place their infant
under the device that employed a conjugate reinforcement system
for 20 minutes five days each week for 12 weeks. In brief, the Kick Start Gym is
designed to reinforce kicking in a supine posture and the Tummy Time Gym is
designed to reinforce reaching in a prone posture. Each time the infant produced
a kick that resulted in the foot touching the kick pad, a short burst of music
and spinning toy resulted in reinforcing the kick. The frequency of kicks in
both groups prior to the intervention was similar. Results following 12 weeks of
the intervention demonstrated that the infants in the kicking group
significantly increased their kicking compared to the reaching group. The
kicking group also acquired the locomotor milestones earlier but did not reach
statistical significance primarily due to inadequate statistical power. Future
research is needed applying Edelmanâ€™s model
to early motor intervention and functional skill development.
Effects of practice in young adults with Down syndrome
Effects of practice on motor coordination are not limited to
early motor development. Several studies have documented rather dramatic changes
in motor performance and in indices of motor coordination in persons with Down
syndrome within a wide range from early adolescence to over 40 years of age[81-85].
Performance of young adults with Down syndrome shows dramatic
improvement with practice even in tasks that are very simple and seem to offer
little room for improvement. For example, when a person without Down syndrome is
instructed to perform a very quick and accurate movement of a joint (e.g., the
elbow) to a target, it takes only a few familiarisation trials to reach a
performance level that remains virtually unchanged in the course of practice. In
contrast, persons with Down syndrome show relatively poor performance in such
tasks prior to practice. Their peak movement velocities are low, the
trajectories show multiple velocity peaks, and muscles crossing the involved
joint show irregular activation patterns, commonly with episodes of simultaneous
activation of flexors and extensors.
However, after only five days of practice, these movements become much faster
(peak speed nearly doubles) with the emergence of a more typical pattern of
A question emerges: Why did not those persons perform the
movements with the typical patterns and characteristics at the onset of the
study? The changed performance was likely due to adjustments at a neural level.
One conclusion is that persons with Down syndrome have all the machinery, both
muscular and neural, to perform movements with characteristics like those seen
in persons without Down syndrome. Hence, their movement patterns that look
clumsy and less efficient to an external observer are likely to reflect adaptive
changes that have to be deciphered.
Effects of practice on coordination have been notoriously
hard to quantify, mostly because of the lack of an accepted quantitative index
of coordination. Recently, a particular quantitative approach to motor synergies
has been introduced that allows us to quantify patterns of coordination of
muscles, joints, limbs, and fingers over a variety of tasks (reviewed in
ref 88). This method
was applied to analysis of multi-finger coordination in persons with Down
syndrome who performed a task of accurate force production by pressing with the
four fingers of the dominant hand on four force sensors[84,89].
Persons with Down syndrome showed patterns of finger force coordination that
were dramatically different from those seen in subjects without Down syndrome.
In a sense, persons with Down syndrome used their fingers as the prongs of a
fork turned upside down pressing with all the fingers stronger or weaker and not
using the flexibility of the hand design.
After only three days of practice, persons with Down syndrome
started to show more typical, flexible patterns of finger coordination such that
an increase in the force of one finger could be accompanied by a decrease in the
force of another finger. Participants in this study who were encouraged to
perform various tasks during practice showed significantly larger improvements
in their performance and indices of finger coordination as compared to those who
practised only the main task.
In a recent study, effects of practice of treadmill walking
were analysed in persons with and without Down syndrome.
These persons produce patterns of locomotion that suggest atypically high values
of the apparent joint stiffness in the lower extremities. Four sessions of
practice have been shown to lead to changes in the stiffness indices towards
more typical values observed in persons without Down syndrome.
Overall, the cited studies suggest that practice can be a
powerful tool for improving motor coordination in persons with Down syndrome
over their lifetime, not only during the early stage of motor development.
Physical activity and health
Individuals with Down syndrome are at higher risk for
overweight and obesity than their typically developing peers. The prevalence of
obesity in Down syndrome is estimated to be higher than in the typically
developing populations, with many studies reporting a prevalence of overweight
between 45% and 56%[90,91,92].
Research over the past 10 years has demonstrated the critical role played by
physical activity in achieving and maintaining health in all children, youth,
and adults, including those with disabilities[93,94,95].
The current guidelines recommend at least 30-60 minutes of moderate-intensity
physical activity (MPA) on most days each week. Healthy People 2010 includes a
section with the overall goal to "Improve health, fitness, and quality of life
through daily physical activity"(see
ref 96: Chapter 22). In this document, specific goals are
set out, including: "to increase the proportion of adolescents who engage in
vigorous-intensity physical activity (VPA) that promotes cardiorespiratory
fitness three or more days per week for 20 or more minutes per occasion" (see
ref 96, item
22-7) and "Increase the proportion of adolescents who engage in moderate
physical activity for at least 30 minutes on 5 or more of the previous 7 days" (ref
96, item 22-6) and "Increase the proportion of trips made
by walking" and "Increase the proportion of trips made by bicycling".
A common characteristic shared by individuals with Down
syndrome and other developmental disabilities is a stable pattern of physical
Multiple reports describing the health related physical fitness of children,
adolescents, and adults with Down syndrome consistently demonstrate that their
physical fitness profiles are inferior to their typically developing age peers.
Poorer fitness places them at higher risk for obesity, type II diabetes,
coronary heart disease, early onset of ambulatory problems, difficulty
maintaining their ability to work, and early morbidity[94,102,103,104].
As a result of these consistent findings, the United States Surgeon General
convened an expert panel in 2001. This panel published proceedings that
highlighted the critical problem of physical inactivity and obesity in people
with intellectual disabilities. The panel recommended that major efforts be made
to meaningfully increase the proportion of persons with intellectual
disabilities participating in moderate levels of physical activity on a regular
Subsequent to the published proceedings, a few intervention studies have been
reported in recent years. One study demonstrated success in improving
cardiovascular fitness, muscular strength, and endurance in adults with Down
syndrome participating in an exercise training programme. This programme was
conducted in small groups, similar to programmes available at a local health
This study is very encouraging as it demonstrates that adults with Down syndrome
can improve their fitness profile. Unfortunately, this study did not measure the
physical activity level of the participants prior to, during, or following
conclusion of the 12 week training programme. There is no current empirical
evidence that demonstrates that improvements in selected fitness parameters will
lead to a significant increase in daily participation in physical activity at a
moderate to vigorous intensity once the experimental exercise programme
concludes. The type of training study described above also assumes that persons
with Down syndrome or their family can afford a membership to the health club.
More studies are needed that specifically measure outcomes related to physical
activity and do so, on a longitudinal basis.
Physical activity levels in children with Down syndrome have
not received much attention in the research literature. Overall time spent in
moderate to vigorous physical activity (MVPA) as compared to typically
developing peers has been documented through direct observation and
When compared to their typically developing siblings, children with Down
syndrome spent less overall time in vigorous physical activity (VPA) and the
bouts of VPA were also of shorter duration[101,107].
In a recent study, parents of children, teenagers, and young adults with Down
syndrome (aged 3-22 years) participated in focus groups, and were asked
questions related to their perceptions of the health and physical activity needs
of their children.
The parents of preschoolers with Down syndrome generally felt their children
were physically active and that it was very important to them to keep them
active to help prevent the onset of obesity they observe in older children with
Down syndrome. Most of the parents of older children and teenagers with Down
syndrome responded that their children were primarily physically active for
social reasons. The presence of a sibling or peer was the prerequisite stimulus
for the child with Down syndrome to engage in a physical activity. In the
absence of a peer or sibling, sedentary activities dominated. Parents of the
older children concluded that they wished someone would have convinced them
earlier that it was extremely important for their child to learn an individual
sport or activity (e.g., swimming, bicycling, bowling) because their childâ€™s
skill level makes it difficult to engage in team sports that are competitive in
Recent medical research concludes that persons with Down
syndrome have increased levels of oxidative stress
and that oxidative damage has been hypothesised as a contributor to the
neurologic, endocrine, and immunological problems, as well as the premature cell
aging observed in this population.
Obesity is also associated with increased oxidative stress.
While some of the consequences of obesity, such as cardiovascular disease and
diabetes, appear to be less common in Down syndrome than would be expected,
given the high incidence of obesity in this population, other diseases
associated with reactive oxygen species and higher levels of oxidative stress,
such as Alzheimerâ€™s disease, are much more common in this population[111,112,113].
Interestingly, from a preventive health perspective, regular physical activity
has recently been reported to improve erythrocyte antioxidant enzyme system in
teenagers with Down syndrome.
These researchers conclude that increasing physical activity may be valuable for
individuals with Down syndrome beyond improving their health related physical
Based on the conclusion that persons with Down syndrome
become more inactive as they move through primary school, serious efforts must
be made to reduce sedentary activity and increase time spent in moderate to
vigorous physical activity most days each week. It is hypothesised that a major
reason for the emerging, inactive lifestyle in children and young people with
Down syndrome, is that most posses a very small repertoire of physical
activities. We must find activities that are: valued by the child and the
family; popular with siblings and peers; increasing community participation;
promoting independence. We must also be innovative in conceiving and testing
procedures to teach children the most critical activities. So, what physical
activity can meet all of these criteria? One excellent option is riding a two
wheel bicycle without training wheels.
A recently completed randomised trial that was funded by the
National Down Syndrome Society, was designed to test the effects of learning to
ride a two wheel bicycle in 8-15 year old children with Down syndrome.
We learned from a survey we conducted of parents in three large Down syndrome
parent support organisations, who have a child in the 8-15 year old age range,
that only 9.7% reported their child could ride a two wheel bicycle at least 9
metres (30 feet). We recruited 61 children and randomly assigned them to an
experimental or control group. The experimental group received individualised
bicycle training for 75 minutes each day for 5 consecutive days (total of 6
hours and 15 minutes). The control group did not receive the training until the
second year of the study. All children participated in a series of measures
prior to training, 60 days post training, and 12 months post training. The most
exciting result was that 62% of the children (experimental and control groups)
who received training, learned how to ride a two wheel bicycle a minimum of 9
metres within the 5 days of training. Needless to say the parents were thrilled.
The other important result was that when we compared the experimental and
control groups at the 12 month follow-up session, the experimental group
displayed significantly less time in sedentary activity and significantly more
time in moderate to vigorous activity compared to the control group that had not
yet received their bicycle training. Parents have experienced great difficulty
teaching their child with Down syndrome to ride a two wheel bicycle and as a
result the child displays a high level of fear in riding that must be reduced if
learning is to occur. We now have the procedures to teach most children to ride
and anticipate important health and social outcomes. Research questions related
to psychosocial benefits, community participation and increasing independence as
a result of learning to ride a two wheel bicycle appear warranted.
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patient with Downâ€™s syndrome. International Journal of Cardiovascular Intervention.
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Heller T. Nutritional status and risk factors for chronic disease in
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training program on physical activity patterns in youth with Down syndrome:
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review in Pediatrics;2008.
Mark A Latash is at the Department of Kinesiology, Pennsylvania
State University, USA
Louise Wood is at the Department of Sport and Exercise Science,
University of Portsmouth, UK
Dale A Ulrich is at the Division of Kinesiology, University of
Dale A Ulrich, 1402 Washington Heights, Ann Arbor, MI 48109-2013. Fax:
734-647-2808. Email: email@example.com
Paper prepared from presentations and discussions at the Down
Syndrome Research Directions Symposium 2007, Portsmouth, UK. The symposium was
hosted by Down Syndrome Education International in association with the Anna and
John J Sie Foundation, Denver. Major sponsors also included the Down Syndrome
Foundation of Orange County, California and the National Down Syndrome Society
of the USA. Information about the symposium can be found at
Received: 21 January 2008: Accepted: 28 January 2008; Published
online: 11 November 2008
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