What do we know about the development of motor skills in children and adults with Down syndrome?

Research into the development of motor skills in children and adults with Down syndrome is limited at the present time.^[1] [TODO: 11-12] [TODO: Add Ringenbach et al 2022, Needham et al 2021] The available research can be divided into two main types - descriptive studies and experimental studies.

Types of research

The studies of infants and children are mainly descriptive. Descriptive studies usually document the ages at which skills are attained. These may be basic gross and fine motor skills, and sometimes recreational skills as well as component skills such as balance, or hand-eye coordination. There have been a small number of experimental studies of children but most of the experimental work has examined the skills of teenagers and adults. Experimental studies usually require participants to learn a new motor action or to carry out actions at speed and then measure various aspects of their performance.

Limits of research

Unfortunately, the findings of many research studies in the area of motor skills have to be interpreted with caution for several reasons.

Small numbers. Researchers have often studied very small numbers of children or adults. Given the considerable variability of progress among children and adults with Down syndrome, it is impossible to judge how representative the performance of such small numbers of children actually is, and therefore whether the findings can be generalised to all other children and adults with Down syndrome.

Date of studies. Some studies from the 1970s and 1980s will include children who grew up with low expectations, little or no early intervention support, and limited social and educational opportunities. Early studies may therefore be difficult to interpret.

Comparison groups. Another weakness of many studies lies in the comparison groups that they use. Many studies of both adults and children compare their motor skills with typically developing individuals of the same chronological age, usually reporting significant differences in performance, with those with Down syndrome having ‘poorer’ skills. However, when the comparison group is matched on mental age, then there are often no significant differences in the overall motor performance of the groups. Any differences that are found tend to reflect strength and balance issues or speed and accuracy of performance, rather than overall motor control. Examples of these findings are given in the relevant sections later in this overview.

Learning and practice effects. One problem that arises when the motor skills of children or adults with Down syndrome are compared with those of others is that it is difficult to control for their past experiences and the opportunities that they have had to develop their motor skills. They will usually have had less opportunity to practise than those they are being compared with. Practice improves motor skills until an optimal level of skill is achieved which does not improve further. In research studies, it is only possible to draw conclusions about differences in motor abilities if the participants are able to practise until they reach their peak performance, and there is evidence that individuals with Down syndrome require significantly more practice than others to reach their peak performance [TODO: Check linking] (see ’ Practice improves performance’).

Practical relevance. A number of studies are of theoretical rather than practical relevance. Currently many researchers are interested in the detailed way in which movements are carried out by individuals with Down syndrome and they measure differences in the angles of joint movements, take measures of the actual activation patterns of muscles, or study the differences in patterns of gait. Most of these studies indicate largely normal movement patterns.^[2] [TODO: 16] Some do indicate difference in muscle activation patterns [TODO: 5],[TODO: 15],[TODO: 17] or joint movements in experimental situations. However, since no one has conscious control over the sequence of actions of muscles or joints when moving, these studies have little direct practical relevance. It is also not clear from most of these studies whether these differences are developmental (i.e. seen in the early stages of learning a skill) and will disappear with practice.

Descriptive studies

The pattern of motor development for children and adults with Down syndrome

One of the important issues in the study of motor development in people with Down syndrome is whether there is delay in achieving milestones and/or whether movements are abnormal or not properly suited for their purpose. Some of the relevant research is considered in this section.

Development is the same but delayed for age

Motor development for children with Down syndrome is usually significantly delayed. All the basic motor skills are achieved by infants and children with Down syndrome in mostly the same order, but usually at significantly older ages when compared with typically developing infants and children. This is illustrated by the examples for gross motor and fine motor skills given in Tables 1 and 2. Note that these tables give the average age that a skill is achieved but also show the wide range of individual differences for both groups of children. The ranges are of more practical relevance.

[TODO: Insert Table 1 and 2 from motor 0-5 - replacing this Table 1]

Table 1. Motor Milestones - A guide to ages of attainment for children with Down syndrome^[3]

There is evidence that some motor skills, such as those requiring fine finger to thumb opposition position (pincer grasp) and those requiring fine control of balance, may be achieved later than is typical and therefore slightly out of the usual sequence. One study of 220 young children with Down syndrome aged 3 months to 60 months^[4] [TODO: Check reference - chapter?] assessed their progress on specific gross and fine motor skills on the Bayley Scales of Infant Development. This test provides norms for the ages and expected sequence of the achievement of early motor skills in typically developing children. This study found that picking up tiny objects, walking backwards, standing on one foot, jumping and walking downstairs without support, were all achieved later than is typical, and late in relation to other motor skills. It seems that it is skills requiring more complex balance control that are achieved later. Balance is discussed more fully in the next section.

There is a wide range of individual differences

There is greater variability in the basic motor progress of children with Down syndrome when compared with typically developing children. For example, the average age for walking in typically developing children is 13 months and the range is 9-17 months, while the average age for walking in children with Down syndrome is 24 months and the range is 14-42 months. Some of this greater variability may reflect the effects of health status for some children. Children with major heart abnormalities may be slower to achieve some motor milestones until they have corrective surgery, and the minority who cannot have corrective surgery will continue to be delayed. Similarly, a small number of children with Down syndrome have additional brain damage and will be more severely delayed in their motor progress. We need to study the progress of large numbers of children and take account of their health status, in order to develop sufficiently detailed data to enable parents and practitioners to accurately predict the progress to be expected of individual children.

Slower progress may not affect final performance

It is important to note that, at present, we do not know whether being a slower starter affects the eventual level of competence achieved in any particular skill. A study of Canadian infants and young children discussed below[TODO: references 11] suggests that, for gross motor skills up to the age of 6 years, the severity of motor impair­ment ‘affected the rate [of progress] but not the upper limit of motor function’.

[11:p.494] Research studies[12,13] and personal experience indicate that, given appro­priate opportunities, motor development for individuals with Down syndrome continues to improve throughout childhood and into adult life. Many adults with Down syndrome can and do considerably improve both fine and gross motor skills when given the opportunity to do so.

The work of Latash and colleagues[14,15] has shown that, with practice, adults with Down syndrome can achieve skills in fine-motor tasks equivalent in speed and accuracy to those of non-disabled adults. The first author’s daughter dra­matically improved her handwriting abilities, her running and her ability to tie shoelaces quickly and competently in her twenties. She did not walk until she was 4 years and 6 months of age and she could not legibly copy her name at 16 years of age. There are several possible factors at work here. It is possible that many children and teenagers are functioning below the levels they could attain because they have not had sufficient practice of motor skills and/or it may be that their nervous systems take much longer to mature and reach peak per­formance. Latash and others[15,16] suggest that motivation may play a part and that, if movements are difficult to carry out successfully, children with Down syndrome may experience frequent failure and, therefore, avoid these move­ments and hence have less practice and experience.

Exploring individual differences

Table 3: The percentage of children with Down syndrome expected to achieve skills at each age point. differences Adapted with permission from Elsevier [11 p.499]

Two useful types of data illustrating the variability of development are provided from a study of 121 children aged 1 month to 6 years involved in a Canadian early intervention programme. [TODO: references 11] The children’s attainment in gross motor function was measured using the Gross Motor Function Measure (GMFM)[TODO: references 17] and the quality of their movements was also assessed.

Rates of progress

The information obtained from the GMFM assess­ments has been analysed to provide guidance on the percentage of children who are likely to have achieved a skill by a particular age. This is presented in Table 3 (0-5 table) . It is another way of showing the wide variability in rates of progress but it is more useful for interpreting and predicting individual progress than just knowing the means and ranges. The criteria for passing the items are given in the box below the table.

The data in Table 3 provide information on the differing rates of progress of children for parents and teachers to use to assess the rate of progress of an individual child, that is, to determine whether the child is progressing faster or more slowly than the average child with Down syndrome. The authors of the article suggest that specific therapy may only be needed when a child is going more slowly than most other children with Down syndrome.

A more important implication would be that interventions should be adapted to the individual needs of the child rather than a specific package offered simply because the child has Down syndrome.

Milestone 6 12 18 Age (months) 24 30 36 48 60 72 Rolling 51 64 74 83 89 93 97 99 100 Sitting 8 78 99 100 100 100 100 100 100 Crawling 10 19 34 53 71 84 96 99 100 Standing 4 14 40 73 91 98 100 100 100 Walking 1 4 14 40 74 92 99 100 100 Running 1 2 3 5 8 12 25 45 67 Climbing step 0 0 1 1 3 5 18 46 77 Jumping forward 0 0 0 1 2 5 18 52 84

Rolling - rolls to prone over side from lying supine (on back) Sitting - sits on floor at least 3 seconds, arms free Crawling - crawls reciprocally forward at least 6 feet (1.82 metres) on hands and knees Standing - stands with arms free and no support for at least 3 seconds Walking - walks forward 10 steps with arms free and no support Running - runs 15 feet (2.74 metres), stops, and returns Climbing stairs - walks up at least 2 steps from the base of the stairs, alternating feet, without holding on Jumping - jumps forward at least 2in (5.08cm), both feet simultaneously

Differences in the severity of motor impairments

In order to explore this issue of individual differences further, the authors of the Canadian study have rated the characteristics and quality of the children’s movements and classified them as having Mild, Moderate or Severe motor impairment based on the ratings of experienced assessors. The assessors’ ratings represent their overall judgement of muscle tone, strength, range of motion, motor control, efficiency of move­ment and quality of movement. In other words, they are not just considering whether a child has reached a milestone and can, for example, sit or walk, but how they do so. Is the child able to sit with a straight back or do they still tend to be leaning forward with a rounded back? Is the child walking steadily with feet forward and a narrow based gait or with a wide based gait, feet turned out and still rather wobbly? The definitions that they used to categorise the children into Mild, Moderate or Severe motor impairment are given in the box above.

Of the 121 infants and young children in the study 51 (42%) were classified as having Mild motor impairments, 64 (53%) as Moderate and only 6 (5%) as Severe. Because only 6 children were classified as Severe, the authors combined them with the Moderate group to make comparisons with regard to rates of progress. Their data indicated that the children in the Mild group progress faster than the rest of the children - about 25% faster. However, all the study children eventu¬ally reached the gross motor milestones. To quote, the authors state that (the degree of) “motor impairment has a discernable effect on rate of improvement but only a slight effect on ultimate achievement of gross motor function in early childhood”.[11:p.497] All children are walking by 5 years of age.

Some skills mastered more slowly than others

All the children in this study showed faster mastery of those skills which are acquired earlier in motor development. The authors suggest that the reason for faster progress with early skills indicates that “children with Down syndrome require more time to learn movements as move­ment complexity increases. The motor control requirements for posture, weight support, muscle force production, and balance increase as children progress from floor mobility to walking, to the ability to perform movements used in play and rec­reation such as running and jumping. During infancy, when GMFM scores improve fastest, children with Down syndrome are developing the ability to sit and move on the floor. Between the ages of 18 months and 3 years, most children with Down syn­drome are learning to stand alone and to walk. The slower improvement in scores during this period may correspond to the increased motor control required to move when standing where the centre of gravity is higher and the base of support smaller and less stable compared to creeping and crawling”.

The authors go on to point out that the slowest improvement was seen between the ages of 3 and 6 years, when most children with Down syndrome are learn­ing to run, walk up and down stairs, and jump. They suggest that this “may reflect the increased motor control required for limb co-ordination, speed and balance”.[11:p.498]

In their discussion of their findings, these authors make three specific obser­vations, which we will return to again later with regard to their relevance for intervention priorities.

Can age of walking be accelerated?

Firstly, they compare their findings for the age at which their children had walked with the data from earlier studies of groups of children with Down syn­drome and found no significant differences in age of walking. The children in their study had received early intervention but the earlier studies provide data on the progress of children before early intervention was available. They sug­gest that this finding may indicate that “early intervention by parents and professionals does not lower the age of walk­ing in children with Down syndrome below constraints imposed by maturation of the nervous or musculoskeletal system”. However, the work of Dale Ulrich and colleagues[TODO: references 18] does indicate that it is pos­sible to accelerate progress to walking by as much as 3 months using tread­mill practice (discussed in detail on page 27), highlighting the need to decide exactly what kind of intervention activities do or do not have an effect.

A focus on playground skills once walking

Secondly, the authors of the Canadian study suggest that there is a need to focus on encouraging running, jumping and stair climbing for the 3 to 6 years olds as these activities are important in playgrounds and will improve the ability to be included socially, as well as affect children’s confidence and self-esteem.

Therapy should be linked to expectations for children with Down syndrome

Thirdly, they suggest that children with Down syndrome whose motor develop­ment is age-appropriate or advanced relative to the expectations for children with Down syndrome, “may successfully achieve motor goals and activities through play and struc­tured developmental activities; ….Conversely, children whose gross motor function is delayed relative to expectations for children with Down syndrome may be less likely to achieve goals without therapy intervention”.

This advice would indicate that at least some 42% of children with Down syn­drome, with Mild motor impairment, will make good motor progress through play and the encouragement to be active like all other children.

In an American study,[TODO: references 19] using a different classification system (based on actual skills the child achieved rather than quality of movement) delays in children’s gross motor skills were rated on a 5 point scale from Mild to Severe (1=Mild, 3=Moderate, 5=Severe). In a group of 27, children 17 (63%) were rated as 1 or 2 - Mild, 6 (22%) were rated as 3 - Moderate, 4 (15%) were rated as 4, and none were rated as 5 - Severe.

This data again highlights the individual differences in motor development for children with Down syndrome and the need to match support and interven­tion to the needs of the individual child. It also emphasises the fact that motor delays may be Mild for about 50% (42% - 60% in these studies) of children, yet many early guides for parents continue to stress the seriousness of motor delays for all children with Down syndrome.

Table 3. The percentage of children with Down syndrome expected to achieve skills at each age point. Adapted with permission from Elsevier [22 p.499]^[5]

[TODO: Format]

Rolling - rolls to prone over side from lying supine (on back) Sitting - sits on floor at least 3 seconds, arms free Crawling - crawls reciprocally forward at least 6 feet (1.82 metres) on hands and knees Standing - stands with arms free and no support for at least 3 seconds Walking - walks forward 10 steps with arms free and no support Running - runs 15 feet (2.74 metres), stops, and returns Climbing stairs - walks up at least 2 steps from the base of the stairs, alternating feet, without holding on Jumping - jumps forward at least 2in (5.08cm), both feet simultaneously

[TODO: “Definitons of motor impairments” - p.11 of 0-5 book]

More detailed and recent norms for gross motor development have been published based on longitudinal clinic data collected on 509 children with Down syndrome from birth to 10 years. The children were all receiving physiotherapy from the same therapist and illustrate the median age a skill was achieved plus the wide range of individual differences. [TODO: Add winders wolter-warmerdam Hickey 2019]

Another study has published more detailed information on gross motor progress of 20 children with Down syndrome from 3 to 12 months. It identifies each small step in progress for the prone, supine, sitting and standing postures through the first year of life. [TODO: Add Pereira, K., Basso, R.P., Lindquist, A.R.R., da Silva, L.G.P. & Tudella, E. (2013)]

Norms have also been published for fine motor skills from clinic records for 274 children from 4 months to 18 years of age. They identify early achievers (10-30% and representative achievers, that is age when most children achieve the skills (75-95%) They give comparisons with expected progress of typically developing children which illustrate that on a number of skills, some early achievers are within the typical range. Frank, A. & Esbensen, A.J. (2015) These published sets of norms all indicate the wide range of induvial differences in progress. We discuss this further in the next section.

Progress in teenage years

There is only one study reporting in detail on the motor progress of older children with Down syndrome and this does not provide any normative data for the achievement of particular scores but it does illustrate continued improvement for most children on most skills from 10 to 16 years.^[6],[TODO: 24] In this study, information on the fine and gross motor skill development of 105 Australian children was studied over a number of years. The children were assessed at regular intervals on the Bruininks Oseretsky Test of Motor Proficiency (BOTMP) which has 8 subtests designed to assess:-

1. Running speed and agility - the speed with which a child can run 13.7 metres, pick up an object and return to the start.
2. Balance - a number of balance items such as standing on one leg with eyes open and closed.
3. Bilateral coordination - a number of items requiring different limbs to be temporally coordinated e.g. synchronised tapping of the right finger and left foot or right finger and right foot.
4. Strength - tasks requiring strength, including sit-ups and push-ups.
5. Upper-limb coordination - items exploring ball skill and manual dexterity (e.g. finger/thumb opposition).
6. Response speed - reaction times to a simple stimulus.
7. Visual-motor control - items involving cutting, drawing and copying, without being timed.
8. Upper-limb dexterity - items needing a sequence of manual movements e.g. posting coins through a slot, and requiring tasks to be completed within a time limit.

The BOTMP provides norms for the typical ages at which specific levels of performance on the tasks will be achieved and age-related scores can be computed for each of the 8 skill areas.

On all the skill areas the group showed some progress between 10 and 16 years. There was considerable individual variability and the rate of the children’s progress was largely predicted by their mental age, rather than chronological age. While there was a close link between mental and motor age, with those with higher mental age scores tending to have higher motor age scores, on most motor subtests the group had significantly higher mean ages for motor skills. All the subtests scores are higher except for balance, which is lower, and response speed, which is at the level expected for mental age. It is difficult to know how to interpret these findings, as it is always difficult to draw firm conclusions when comparing age-equivalent scores in different areas of development when the tests used have been standardised on different groups of children at different times.

Looking at a subgroup of 16 boys and 13 girls for whom consistent longitudinal data was available, the boys scored higher than girls on running speed and agility, strength, and upper-limb coordination. While a number of the teenagers were reported to be overweight (the Body Mass Index Scores were analysed for the whole group), there was no measurable link between being overweight and motor skill achievements on the BOTMP tests at this early stage of adolescence.

Clumsiness and refinement of movements

Some authors observe that many movements continue to seem somewhat ‘clumsy’ in individuals with Down syndrome.^[7] It takes them longer to improve their skills and they may not reach quite the same levels of fine coordination that most of us take for granted, but the levels they do achieve will usually be adequate for successful performance. Improvements in basic fine motor skills such as tying a shoelace or writing often continue to improve through early adult life. However, it is important to stress the wide variability in progress again, as many children and adults with Down syndrome do not seem at all ‘clumsy’ when walking, running, picking up a cup, writing, skiing, skateboarding or doing gymnastics. The final level of co-ordination and skill achieved seems to have much to do with encouragement and opportunities to take up sports and to practice. We know many individuals who have achieved high levels of competence in basic, recreational and employment skills, and therefore we should never assume that having Down syndrome necessarily puts an upper limit on what a particular individual may achieve.

More difficulty with balance and strength

A number of studies^[8] [TODO: Missing text]

(However, recent intervention studies suggest that more young people with Down syndrome can master a two wheel bike with adapted instruction and this is discussed later in the intervention section).

Strength also tends to be less even when the comparison is with young people of similar age and general mental abilities.^[9] [TODO: 26] The explanation for this is not clear. Everyone increases their muscle strength through active movement and it could be that individuals with Down syndrome engage in less active movement.

Active movement matters

There are now some studies looking at the active movements of infants which do suggest links between amount of physical activity and motor progress. These are discussed in xxxx [TODO]. It could be that children with Down syndrome need more exercise to reach the same levels of strength. This is another area where we know from our practical experience that there are considerable individual differences, with some teenagers with Down syndrome being as strong or stronger than their non-disabled peer group in school. Teenagers who do gymnastics, karate or weightlifting, for example, can be as strong as non-disabled peers, so again, having Down syndrome per se does not impose upper limits on strength. . However, some studies do identify that teenagers and adults with Down syndrome may not be as physically active as their peers. In a study of 104 young people with Down syndrome aged 8 to 16 years, the findings indicate that activity decreased with age [TODO: Add Esposito, P.E., MacDonald, M., Hornyak, J.E. & Ulrich, D.A. (2012)]. Activity was monitored during waking hours over 7 days with a monitor on the right hip during waking hours. The 10-11 year age group was the most active with older teens spending more time in sedentary activities. Vigorous activity was limited at all ages with only 20% engaging in more that 60 minutes a day. While almost half of the teenagers (45.5%) were overweight or obese this was not linked with activity patterns in the study but that does not mean that it is a concern for both health and activity. A later study by the same research team [TODO: Add Pitchford, E.A., Adkins, C., Hasson, R.E., Hornyak, J.E. & Ulrich, D.A (2018)] compared 22 12-18 year olds with Down syndrome with and 17 age matched typically developing young people on measures of weight and body fat, puberty stage and moderate to vigorous activity. The young people with Down syndrome had higher weight measure and lower activity rates than their peers. Their activity rates were more closely linked to body fat rather than BMI. Body fat was influenced by puberty.

Experimental studies of movement skills

Studies which compare children or adults with Down syndrome with typically developing individuals of the same age almost always report differences or delays.[TODO: References to be added?] These comparisons are of limited value as we need to know if these differences simply reflect developmental immaturity - that is, are the individuals with Down syndrome carrying out the task as a younger person of similar mental age would? This is the only way to identify any differences which would have a practical implication for therapy or teaching approaches. We have focused, therefore, on reporting studies that include mental age matched comparison groups and discuss some representative examples of these studies.

Laboratory studies of basic skills

Some experimental studies have looked in detail at the way in which basic skills such as reaching and grasping or walking are carried out by children and adults with Down syndrome, others have studied the ways in which they perform experimental movement tasks.

Reaching and grasping. In a study of reaching and grasping - the movements used throughout the day to handle objects, the skills of 12 children aged 8 to 10 years with Down syndrome were compared with two groups of typically developing children, one of the same age and one younger and mental age matched.^[10] The researchers report that the performance of the children with Down syndrome was essentially the same as that of the younger children. They performed the tasks at the same speed and showed the same ability to adjust their grasps for the size of the object to be picked up as the younger children. They mostly showed the same use of a pincer grip, although 2 children with Down syndrome had unusual grasps, with a tendency to use the palm and all their fingers, rather than finger and thumb. There was more variability in the movement patterns, and a little less accuracy, which the researchers suggest indicates that more practice would be needed to establish more effective motor patterns. Overall, the study indicated that reaching and grasping were delayed rather than different. Similar findings, indicating the ability to adjust to the size of the object, are reported in another study of grasping in 4 to 11 year olds with Down syndrome.[TODO:40]

There are more recent studies of reach and grasp movements in children aged between 4 and 18 in different studies but as they are compared with children of the same chronological age the differences in movements and strategies reported are difficult to evaluate as the children with Down syndrome will have different experiences and opportunities to practice. Some progress with age is reported. [TODO: Refs Jover 2010, Jover 2014 Valvano 2017]

Some research groups have studied the development of reach and grasp longitudinally and have also looked at how children explore objects once they can grasp them. One study flowed 9 infants with Down syndrome and 9 typically developing peers from 4 months of age and then for two further months from the time that they first reached. [TODO: de Campos, A.C., da Costa, C.S.N., Savelsbergh, G.J.P., & Rocha, N.A.C.F. (2013)]

Some infants started to reach by 4 months including 4 with Down syndrome, others at 5 months (3 with Down syndrome) and the remaining two by 6 months of age. The infants with Down syndrome reached for and explored objects less frequently. Reaching increased with age but not exploring objects. This study highlights the links between motor and cognitive delays as less object exploration means the children are learning about objects more slowly. The implication of this is that more support for their experience of handling objects may be important.

In another study by this research team, they do report improvement in reaching strategies and using both hands (bimanual reaching) over time in 4- 8 month olds with Down syndrome. They also report that the infants were less able to adjust to object sizes and identify the need to give them experience of a range of sizes. [de Campos, A.C., Cerra L.C.V., Dos Santos Silva, F.P. & Rocha, N.A.C.F. (2014)]

[TODO: Add Wills Haptic matters]

Walking

[TODO: add Virji Babul, Maiano refs ]

In a study of the walking patterns of children and adults with Down syndrome, 5 children aged 4 to 9 years and 3 adults of 30 to 38 years were compared with a typical adult of 22 years on several tasks, walking and running in bare feet on a hard floor, walking on the elastic surface of a trampoline and walking on a narrow beam. The researchers report^[2] p.79,80 that the walking patterns of the children with Down syndrome on a hard floor were very similar to those of the adults with Down syndrome and the typical adult. The movements of their joints are described as showing ‘very smooth trajectories’ and to ‘resemble adult patterns of walking’. The children and adults with Down syndrome also showed patterns of co-ordination similar to that of the typical adult when running. There was some evidence of differences in the precise details of the range of joint and limb movements but the overall picture was of effective, smooth and largely normal movement. As this study does not include any mental age matched children or adults for comparison, any reported differences may only indicate immaturity at this point. On the trampoline and the balance surfaces, the children and adults with Down syndrome had more difficulty. Both tasks require more skill in balance and they were less able to manage these tasks competently than the typical adult. The changes that they showed in their knee movements and step lengths were attempts to compensate for balance difficulties. Here again, with no mental age comparison and small numbers, the significance of these patterns cannot be interpreted. They could indicate ongoing difficulties with balance, and/or delayed progress. A more recent study of walking explored gait initiation when moving from standing to walking in 17 adults with Down syndrome form 17 to 40 years and 19 aged matched typical peers. They report differences on a number of measures but again these are difficult to interpret and intervention studies which provide practice are needed to see if this results in changes to a more typical pattern. [TODO: de Campos, A.C., Cerra L.C.V., Dos Santos Silva, F.P. & Rocha, N.A.C.F. (2014)]

Laboratory studies of specific movements

Slower reaction times

When teenagers and adults with Down syndrome are asked to perform motor tasks in experimental situations, such as tapping a particular button when a particular light comes on, their reaction times have been reported as slower than those of typical individuals of the same age and the same when compared with mental age matched controls.^[11] [TODO: 15] However, in some studies there is a difference in reaction times for people with Down syndrome when instructions are visual rather than verbal. They show faster reaction times when instructions are visual and show significantly slower reaction times when the instructions are verbal. In everyday life, reaction times influence the speed of starting a movement from the time an instruction is given, for example, at the start of a race.

Slower movement times

Some studies have reported slower times (compared with mental age matched groups) for the movement component of tasks as well as the reaction time.^[11] [TODO: 15] The movement time is the time taken from the initiation of the movement to reaching the end point of the movement - for example, the time taken from initiating the movement to completing the tap in the reaction time task. Individuals with Down syndrome show slower movement times on experimental tasks when instructions are verbal, but when instructions were visual, their performance was the same as mental age matched peers. [TODO: 14] One research group suggests that this indicates a specific verbal-motor impairment in individuals with Down syndrome and that this may reflect different brain organisation for movement control,[TODO: 27] but this hypothesis needs more research.

Delayed but visual learners

Overall, this group of leading movement researchers identify that research studies consistently show that the development of motor skills of individuals with Down syndrome is essentially delayed rather than different. It is linked to progress in general mental age and progresses in a typical but slower way, except for the specific difficulty in processing verbal instructions. They conclude therefore that “a developmental model of information processing and skill acquisition should be used to guide the instructional protocols used by clinicians, teachers and parents attempting to optimise skilled performance”.^[11] p. 67. The advice to use a ‘developmental model’ means that parents and teachers should expect movements to be achieved and improved in the same way as they are in typically developing children and adults, although more slowly. Teaching activities should, therefore, be those appropriate for the stage of movement skill that a child or adult has achieved. The practical implications of the verbal instruction findings are that, within a developmental framework, instructions for motor activities of all kinds, from writing to dancing, should be by modelling or demonstrating actions whenever possible. There are, in fact, studies showing that the motor areas of the brain which control movement are activated by passively watching a movement, which may partially explain the advantage of learning by watching, rather than by verbal instruction.[TODO: 45]

Practice improves performance

Data from experimental studies requiring fine motor tasks to be carried out^[12],[TODO: 15] and from real life studies of activities such as running,[TODO: 28] report significant improvement in the performance of tasks with practice - improvements in both speed and accuracy of movements. For example, a group of adolescents with Down syndrome enrolled in a physical training programme showed considerable improvements as a result of training. The mean time to run the 50 metre dash dropped from 15.39 to 10.69 seconds. However, some of these studies concluded that individuals with Down syndrome require about twice as much practice to reach the same level as typically developing individuals of the same mental age.[TODO: 28] They seem to need more practice to establish motor programmes.

The positive effects of practice are well illustrated in a series of studies^[13] -[TODO: 31] in which the researchers compared the performance of 10 adolescents with Down syndrome, average age 16 years, with that of 3 other groups of students; one group of the same age with learning disabilities but not Down syndrome, one group of typically developing high school students of the same age and one group of younger typically developing children of the same developmental age. The young people were asked to perform a pursuit-tracking task (see [Figure 2]) which requires them to move the pointer to the target light. The pointer is moved by turning the steering wheel and once the pointer has been on that target light for 200 milliseconds, the light goes off and another comes on. The pointer then has to be moved to that light. In one trial of 100 moves, the lights come on in a pattern that requires 50 moves to the right and 50 moves to the left. The probability of moving in a particular direction varies according to current position, as illustrated in [Figure 2]. If the pointer is on the far left light, there will be 100% probability that the next required move will be to the right and if the pointer is on the middle light, the probability of moving right or left is the same - 50%. The probabilities for each light are illustrated in the figure. In the studies, the researchers were interested in the speed (measuring both reaction time and movement time) and accuracy with which the young people could carry out the task, and whether they used the probability information to improve their performance.

!

Figure 2. Pursuit tracking device

Speed and accuracy

In the first study^[13] the young people carried out 8 trials comprising 800 actual moves of the pointer. The young people with Down syndrome scored at the same level on reaction times as their peers with learning disabilities and both these groups were slower than the typically developing high school and elementary school students. On movement times the pattern was the same. However, on accuracy, the young people with Down syndrome were significantly better than all the other groups - therefore they were even more accurate than non-disabled peers of the same chronological age. They were slower than their non-disabled peer group but they made fewer errors. The mean error rate for the group with Down syndrome was 8%, and for the learning disabled and high school groups 13%. However, the young people with Down syndrome did not show any evidence of making use of probability data, that is, they did not react faster when it was possible to predict the likely direction of movement, although the other groups were able to do this.

Reaction times improve with practice

These researchers went on to extend this work^[14] and in another study using the same groups and design, they increased the amount of practice to 24 trials and, therefore, 2400 moves. For reaction times, again, the typically developing high school students were faster, but the other 3 groups were not different from one another - that is, the young people with Down syndrome were as fast as the younger typically developing children and their peers with learning disabilities. This time, having been given much more practice at the task, the young people with Down syndrome did show evidence of using probability information when reaction times were analysed to take account of this, i.e. the more predictable the direction to move in for the next light the faster their reaction time. However, their reaction times continued to be longer for longer movements, and this is not easy to interpret.

Slower but more accurate

For movement times, the young people with Down syndrome were slower than all the other groups but again, they were more accurate - they made fewer errors than all the other groups.

When given sufficient training, the young people with Down syndrome significantly reduced their reaction times - they were about 36% faster in reacting and initiating movements, but they did not improve their movement times. They seemed to focus on accuracy and were unwilling to increase speed. This is entirely sensible as, in all studies looking at speed and accuracy on this sort of task, there is a link or ‘trade-off’ as a point is reached where it is not possible to improve one without a negative effect on the other; after this level of performance has been reached, an increase in speed leads to a decrease in accuracy (this is called Fitt’s Law).

Individual differences

Within the group of 24 young people with Down syndrome who took part in one of the studies^[15] using this task, the performance of individuals tended to be linked to general mental age, that is, those with higher mental ages did better on the tasks than those with lower mental ages.

The importance of practice

These general findings of improvement with practice, slower movement speeds and a focus on accuracy rather than speed have been confirmed in other studies.^[16] Many studies indicate that teenagers and adults show considerable improvement with practice. This indicates that they have not yet reached their optimal levels of performance, possibly because they have not had enough opportunity to practise both gross and fine motor skills during childhood. In some studies, their performance after practice is as good as typically developing individuals of the same age.[TODO: 5],[TODO: 43]

[TODO: Consider splitting here with rest in new article]

Why this profile of development?

At the present time, we do not have enough knowledge about the reasons for these features of motor development in individuals with Down syndrome but we do have several facts which may provide some clues and guidance for more effective intervention.

Closely linked to mental age

Both the descriptive studies of children’s progress and some experimental studies of motor skills in adults identify that the motor performance of individuals with Down syndrome is closely linked to their general cognitive progress. In other words, for gross motor, fine motor and experimental tasks, they usually perform like other children or adults with the same cognitive or mental age. This suggests that the main effect is delay rather than difference in motor progress. Movement for some tasks may need some planning so will be influenced by cognitive progress. The link may also suggest that movement abilities influence cognitive progress. A number of recent studies and reviews highlight the effects that motor developments and delays have on cognitive, language and social development. These point is discussed further [TODO]

Early childhood

A link between mental and motor development

Some studies suggest that, for infants,[TODO: references 22] children[TODO: references 23] and teenagers[12,13] with Down syndrome, motor development progresses at about the same rate as mental development, when progress is measured on standard assessments which sample a range of motor and mental 35 tasks. The similar rates of progress are illustrated in ###### Figure 1. These graphs show 30

the rates of progress of 220 children as

25

assessed on the Mental and Motor Scales of the Bayley Scales of Infant Develop­ment. The graphs are actually based on 707 Mental Age (months) 20 15 10

assessments, as some of the children were assessed at several different ages as part of longitudinal studies. This data is the result of an international collaboration and includes children in Australia, Canada and Germany. It is the largest data set that is available. The papers published on this study do not actually state the statistical correlations between the mental and motor scores of the children and, therefore, we should be cautious about interpreting the similar rates of progress suggested by the graphs. If the 5 0

Figure 1. Mental and motor progress in children with Down syndrome from birth to 5 years (Adapted from [22, p.339] with permission)

rates of progress are similar for each child, we would have graphs like these but if some children have motor skills ahead of mental skills, and a similar number have mental skills ahead of motor skills, then the pooled data would still look the same.

Personal communication with several authors has provided some relevant infor­mation on this issue. Hellgard Rauh, at the University of Potsdam in Germany has shared unpublished data with us on the 202 children in the international study illustrated in the graph. This indicates that some children do show very similar rates of mental and motor development, while others show a little more varia­tion - usually with motor progress slightly behind mental progress between 12 months and about 36-40 months of chronological age, sometimes longer. Her data indicates very high correlations between mental and motor scores on the Bayley Scales (correlations of .93 at 6 months, .81 at 15 months, .78 at 36 months and .79 at 48 months, with a smaller correlation of .54 at 24 months - possibly reflecting late walking).[Rauh - personal communication]

Cliff Cunningham at John Moores University, Liverpool, UK, found Bayley Mental and Motor Scale correlations of .59 at 6 months, .67 at 10 months, .55 at 15 months and .64 at 24 months in his large Manchester cohort of 150 children with Down syndrome.[Cunningham - personal communication] He also pointed out that up to the 15 month level some 60% of the items on the Bayley Mental Scale require motor skills in order to complete them (e.g. to build blocks and to manipulate objects), therefore high correlations would be expected. Gerald Mahoney of Case Western Reserve University, Ohio, USA, found correlations of .71 between the Bayley Mental Age scores and Peabody Motor Age scores for 27 children with Down syndrome at 14 months and a correlation of .53 at 26 months. [Mahoney - personal communication] These are the children in the study of early intervention reviewed on page 23.

Later childhood

Two studies of older children[12,13] do also indicate significant correlations between motor scores and mental scores for children with Down syndrome.

Figure 3. Mental and motor progress in children with Down syndrome (Adapted from^{[17(p. 339)]}

Later childhood

One American study charted the progress of 15 children with Down syndrome who were 7 to 10 years of age, and who had had the advantage of well-organised early intervention and education. The findings in [Table 3] show the close relationship between their mental and motor progress. For the reader interested in the data, the correlations between the fine motor and gross motor skills and mental age are both .64 and statistically highly significant.^[18] A study of 99 Australian 10 to 16 year olds with Down syndrome also showed the close link between motor skills and mental age, with the children’s mental age rather than their chronological age, predicting performance and progress.[TODO: 23],[TODO: 24]

Table 4. Relationship between mental and motor progress in children with Down syndrome. Based on data published in^{[18 Table 2, p.1317]}

The reason for the close association of overall mental and motor development is not clear, but it may reflect that the control of motor skills is largely a central nervous system activity and that brain functions play a central role in motor development in the same way as they do in other aspects of development. It could be that both mental and motor development are delayed by similar differences in brain processes. One of these differences could be speed of information processing in the brain. Another could be the ability to establish learned programmes in the brain. A number of studies have highlighted the inconsistent performance of children with Down syndrome on both cognitive and language tasks. It seems to take them longer (i.e. they need more practice) to effectively consolidate new learning.^[19]

Individual variability

The reader should note that the close link between the development of mental and motor skills indicated in these studies does not mean that this close correspondence will apply to every individual child at any particular stage. For example, a particular three year old with Down syndrome may be making rapid progress with language but still not be walking, another three year old may show the opposite profile, walking but not yet talking. The overall mental and motor age scores used in these studies are each based on a large number of tasks to give an overall picture of mental and motor development and there will be variability in the way individual children achieve their overall scores. However, the link between overall mental age and progress in overall motor skills is a powerful trend in all studies that have looked at both, and is clearly of significance in understanding the issues.

More dependent on visual feedback

Researchers have reported that children and adults with Down syndrome rely more on visual feedback while carrying out a task than typically developing individuals.^[20] [TODO: 35] They may need to rely to a greater extent on visual feedback because they take much longer to establish learned motor programmes for the task. This can make their performance seem as if they are tackling each repetition of the task as if they have not performed it before. It also means that their pattern of movement may be jerky and inconsistent from one time to the next even though they can actually perform the task correctly. This finding could explain longer movement times because, as a learned programme is established, the sequence of movements required for a movement can be performed more quickly.

Balance

As already identified, there is some evidence that balance may be a particular difficulty for individuals with Down syndrome. In one experimental study, the balancing abilities of infants with Down syndrome were compared with typically developing infants and the two groups were carefully matched for their ability to stand unsupported.^[20] The infants were put into a small room in which the floor was stable but the walls could be moved to give the impression of the room tilting. All the infants reacted as if the floor was also tilting by leaning, swaying, staggering or falling, that is, they reacted as if to stop themselves from falling even though the floor they were standing on did not move. The visual information suggested they were being tilted even though the vestibular and proprioceptive feedback would not have suggested this.

The children with Down syndrome were more affected and made larger postural adjustments than the typically developing children. Both groups of children improved as they increased their experience of walking and after some 12 months of walking the typically developing children were finally able to stay stable in the tilting room and not react to the false visual cues. The children with Down syndrome needed longer to become stable and did not show complete stability after a year or more of walking experience, even though they were improving. The authors suggest that these findings indicate that children with Down syndrome are more dependent on visual cues to judge body position than typically developing children at the same stage of walking, because they need extra visual information to compensate for less effective vestibular and proprioceptive feedback at this stage.

Another similar study of 26 older children with Down syndrome (mean age 10.6 years) showed that they were still more affected by this kind of experience and showed more body sway than other children of the same age.^[21]

There is other evidence to suggest that balance continues to be an area of specific difficulty into the teenage years. In an Australian study of the motor skills of 81 twelve year olds,^[6] [TODO: 24] balance was the weakest area and still at a 4 year level when their other motor skills range from 5 to 9 year levels. Their mean mental age was 4 years 9 months and therefore most of the motor skills for the group were higher than might be expected, with response speed at the same level as mental age and only balance lower than mental age. There was considerable variability in motor skills between individuals and, as in other studies, mental and motor skills were related. Individuals with lower mental ages tended to have lower motor skill scores, and vice versa.

Physical differences

Many authors assume that the profile of motor development in Down syndrome is largely the result of physical differences, but the evidence for this point of view is limited. Almost every discussion of motor development in children with Down syndrome starts with descriptions of hypotonia and lax ligaments, and suggests that they are to blame for the motor delays.

Hypotonia and lax ligaments

Many newborn children with Down syndrome have very flaccid muscles and are described as ‘floppy’. There are many specific disorders which are associated with the birth of ‘floppy’ infants; in some cases this disappears as the child develops and in some cases they remain in this ‘floppy’ state. There are a few follow up studies of infants with Down syndrome and it seems that this infant floppiness does improve over time. There is a fairly widespread belief that the children remain with a degree of hypotonia and this state is often invoked as being responsible for much of the ‘poor’ motor function seen in people with Down syndrome.

However, this is a rather controversial issue since there is no proper agreement as to the definition of hypotonia and there is no consensus as to how to measure it.[TODO: Add Latash, Wood, Ulrich 2009] In addition, some studies have demonstrated that the hypotonia seen when children and adults with Down syndrome are not moving (i.e. their tendency to have more ‘floppy’ muscles at rest) is not evident when they are moving and does not actually impair coordinated movement.^[22] [TODO: 15]

It is generally accepted that ligaments and tendons in individuals with Down syndrome are more ‘stretchy’ than is usual. This would explain why they are often able to move their joints into extreme positions. However, research indicates that this does not prevent coordinated control of the joints to perform ordinary movements.^[22] [TODO: 15] Both muscle ‘tone’ and ‘lax ligaments’ improve with age and with movement, and there is no convincing evidence that these factors affect the development of movements, i.e. the brain is likely to be compensating for them as the child moves.

[TODO: Box from p.17 0-5 book - “Definitions”]

Importance of appropriate comparisons

However, researchers also agree that the ligaments become less ‘lax’ and joints become more stable over time and one problem with evaluating the role of ‘hypotonia’ or lax ligaments in the motor progress of children with Down syn­drome, is the tendency for most observers to be comparing infants and young children with Down syndrome with typically developing infants and children at the same chronological ages. When the comparisons are with children of the same developmental ages, then differences often disappear.

For example, in one study of infant motor development,[TODO: references 30] the researchers actu­ally measured a number of the physical characteristics of the children including the following range of joint movements - hip flexion, hip abduction, knee flex-ion, ankle plantarflexion, ankle dorsiflexion (see box) and the following body size, weight and fat measures - foot length, crown-heel length, crown-rump length, thigh circumference, umbilicus fold, thigh skinfold, calf skinfold and weight.

Ten infants with Down syndrome, with a mean age of 22 weeks, ten typically developing infants of the same chronological age, and ten typically developing infants at the same stage in their motor development and a mean age of 15 weeks, were included in this study. There was only one significant difference between the infants with Down syndrome and the typically developing infants at the same stage in motor development on the above list of measures and that was that the infants with Down syndrome were able to abduct their hips to a greater degree. On all the other measures, the infants with Down syndrome showed the same physical characteristics as the younger typically developing infants. It might be concluded that their movement abilities were appropriate for their physical size and that their joint characteristics, with the exception of hip abduction, were typical for their stage of motor development and motor experience. It seems that the significance of ‘hypotonia’ and lax ligaments has been repeatedly and wrongly over-emphasised in ‘explaining’ motor progress in children with Down syndrome.

To stress the importance of making developmentally appropriate comparisons, we include a further example drawing on the views of a respected researcher in this field, Esther Thelen.[TODO: references 31] In emphasising the difficulties of children with Down syndrome, their early walking is often characterised as abnormal, with a wide based gait, stiff knees and short steps. Yet these features of walking in children with Down syndrome may just be reflecting the stage of walking that they have reached.

The reader might like to refer to the quote in the box on the right, which describes the progress of typically developing children.

The point being emphasised here is that it is important to compare the movement abilities of children with Down syndrome with typically develop­ing children at the same stage of motor development, rather than the same chronological age, in order to understand their movement delays or difficul­ties. This is not easy to do as, even when a child with Down syndrome can, for example, walk 20 feet or 6 metres, they may not be as active every day as a typical toddler and therefore not getting as much practice in order to improve strength, improve balance and refine co-ordination and control of the movement. In addition, research studies indicate that individuals with Down syndrome need more practice than others to achieve a specified amount of progress (see the overview book on motor skills development).

Clearly, a great deal of research needs to be done to clarify the different contributions of the stretchiness of ligaments and tendons, the strength of the muscles, the ‘tone’ of the muscles and the contribution of the nervous input to the greater picture of motor function in individuals with Down syndrome.

Health issues

Some authors rightly draw attention to a number of medical conditions that are more common in individuals with Down syndrome and which may affect a child’s or adult’s ability to be active, if not effectively treated.^[1] [TODO: 11] [TODO: 36] These include heart conditions, underactive thyroid function, vision and hearing issues, atlanto-axial instability and obesity. It will be important to take account of health factors for individual children and adults when considering active sports but most will not prevent progress in basic gross or fine motor skills. The relevance of each of these illness conditions for activity will be the same as it is in the rest of the population.

Parents and carers are likely to know about their children’s medical and healthcare needs and will inform teachers and therapists. Some authors also draw attention to the tendency for individuals with Down syndrome to have small stature and small hands relative to typically developing individuals. However many, if not most, have similar stature to those at the small end of the general population and the restrictions this imposes on achievements in sports will be the same for both groups. [TODO: Review] More information on health issues for children with Down syndrome can be found in each age-specific overview in the DSii series - see [Resources] list.

The effects of experience and practice

However, training studies are needed to properly evaluate the achievable levels of motor skills for children, teenagers and adults with Down syndrome. No comparative experimental studies of motor development in young children have measured the effect of training. They usually compare the performance characteristics of individuals with Down syndrome and typically developing individuals on the same number of trials in the laboratory and then draw their conclusions. However, there is no way of taking into account the amount of practice the individuals have had at the motor skill in question during their lives to this point. Even when individuals with Down syndrome are compared with younger, motor-age matched individuals, it is likely that those with Down syn¬drome have not been so active and have actually had less natural experience and practice. One way of tackling this problem is to train those taking part in the studies on the skill being measured until they no longer show improve¬ments and then make the comparisons. Some individuals with Down syndrome become very skilled as swimmers, skiers, dancers, and gymnasts, showing that the upper limits of achievement for individuals with Down syndrome are very much higher than is often suggested.

Being able to take into account the effect of practice in research is particularly important, as studies indicate that adolescents and adults with Down syndrome need more practice trials to improve performance than other people (see the overview book on motor skills development). Is typical development an appropriate comparison?

Some respected researchers in this field such as Mark Latash and colleagues [15,16] argue that it is not appropriate to compare the motor skills of children or adults with their typically developing peers as the differences in their nervous systems and physical make-up can be expected to produce movements that are different in perhaps both characteristics and quality. These researchers argue that the goal should be to help individuals with Down syndrome to become as effective as they can be through a wide variety of experiences and practice, allowing them to develop their motor skills in the way that is best for them and therefore not try to make their movements conform to what is considered ‘normal’ or typical. This view may have some implications for approaches to physical therapies. One problem other experts may have with this approach is the concern that preferred but atypical ways of moving might lead to long term orthopaedic or other problems, although there is no evidence that this is the case. Longitudinal studies are needed to settle this question. In practice, if a child wishes to get around the floor using an unusual movement there is little a parent can do to change this.

Visual learners

Research with adolescents and adults with Down syndrome highlights that they learn motor skills more effectively from watching a person model the action, rather than from verbal instruction.

In summary

The movement skills of children with Down syndrome are largely delayed rather than different and progress at the same pace as their general mental development. They may take longer and need more practice to improve their performance and they may continue to have more difficulty with tasks requiring balance. Most children achieve competence in all everyday gross and fine motor skills even though they develop more slowly. Despite the presence of lax ligaments and possible hypotonia, there is little evidence that they impair controlled movements as the central nervous system controls all movement and usually compensates for such variables.

Teenagers and adults with Down syndrome may be slower to perform movements in some situations, possibly reflecting slower information processing in the central nervous system and/or a focus on accuracy and safe, effective movements rather than on speed.^[7]