Course:KIN366/ConceptLibrary/Muscular Dystrophy

Movement Experiences for Children
KIN 366
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Instructor:	Dr. Shannon S.D. Bredin
Email:	shannon.bredin@ubc.ca
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Important Course Pages
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	Course Discussion

Overview of Muscular Dystrophy and Movement Experiences for Children

Muscular Dystrophy is a set of heterogeneous inherited disorders that causes severe muscle degeneration and muscular weakness (Lovering & Porter & Bloch, 2005). The effects of this disorder vary depending on the type of muscular dystrophy, however, most children will display muscle wasting and a developmental delay (MacIntosh & Gardiner & McComas, 2006). Motor Development observes the change in motor behaviour and is influenced by biological and environmental factors (Gabbard, 2009). Quality of life for children with muscular dystrophy can be improved by providing them with appropriate equipment and supports, along with affordances such as a daily stretching and exercise regime (Bushby et al., 2009). Both the teacher and the parent of the child with muscular dystrophy should become familiar with different movement constraints and understand ways in which the task or environment can be manipulated to overcome these constraints (Haywood & Getchell, 2009). Understanding the health concerns and need for movement intervention is necessary to optimize development and to allow these children to maintain motor skills and movement patterns as the disease progresses.

The Function of Skeletal Muscle

Skeletal muscle is a type of striated muscle tissue controlled by the somatic nervous system (MacIntosh et al., 2006). It is one of three major muscle types in addition to cardiac and smooth muscle (MacIntosh et al., 2006). Skeletal muscle is composed of myofibrils made up of actin and myosin filaments, which form sarcomere units (MacIntosh et al., 2006). A sarcomere is the basic functional unit of the muscle fiber and allows muscle contraction to occur (MacIntosh et al., 2006). Muscle force is proportional to physiologic cross sectional area and muscle velocity is proportional to muscle fiber length (MacIntosh et al., 2006). The ability to generate a controlled force that is finely regulated is done through voluntary control of the rate and extent of motor unit activation (MacIntosh et al., 2006).

The Function of Dystrophin

Dystrophin is involved in the anchoring of sarcolemma proteins to the cytoskeleton in a muscle fiber and functions to support muscle fiber strength and reduce muscle stiffness (Ervasti & Sonneman, 2008). In skeletal muscle, these complexes function together in mechanical stabilization of the sarcolemma against stresses imposed during muscle contraction (Ervasti & Sonneman, 2008).

Muscular Dystrophy

Muscular Dystrophy is a genetic disease caused by the absence or abnormal expression of the dystrophin gene located on the X chromosome (Lovering & Porter & Bloch, 2005). The lack of this protein complex causes membrane destabilization and defective intracellular calcium handling resulting in abnormal muscle protein degradation (Lovering & Porter & Bloch, 2005). The absence of the protein also impedes the muscles ability to tolerate conformational changes induced by contraction (Leung & Wagner, 2013). This leads to a series of deficits initially involving skeletal muscle wasting and progressing to limited use of all striated muscle including cardiac and smooth muscle (MacIntosh et al., 2006). A defective gene on the X chromosome for Dystrophin causes Duchene Muscular Dystrophy where the dystrophin protein is absent (Anderson & Head & Morely, 2002). A mutation in the dystrophin gene can also lead to a partially functional dystrophin protein, which results in a milder form of Duchenne Muscular Dystrophy known as Becker muscular dystrophy (Aartsma-Rus & Van Deutekom & Fokkema & Van Ommen & Den Dunnen, 2006).

Classification

There are nine types of muscular dystrophy but the most common are Duchenne and Becker muscular dystrophy (Lovering & Porter & Bloch, 2005).

1. Duchenne: Severe X linked recessive genetic disease due to the absence of the dystrophin protein in muscle tissue causing progressive muscle wasting. Onset is approximately 2-6 years (Lovering & Porter & Bloch, 2005)
2. Becker: Has a later onset occurring during adolescence and a longer survival period but is caused by a mutation in the DMD gene encoding the cytoskeletal protein dystrophin (Blake & Weir & Newey & Davies, 2002)
3. Limb Girdle: Muscle weakness affects the shoulder girdle and pelvic girdle first and the progression is slow (Lovering et al., 2005)
4. Congenital: Onset occurs at birth, general muscle weakness and joint deformities (Lovering et al., 2005)
5. Distal: Onset is late at 40-60 years and includes weakness of muscles of the hands, forearms and lower legs with slow progression (Lovering et al., 2005)
6. Emery-Dreifuss: Onset is from childhood to early teens and includes weakness of shoulder and upper arm (Lovering et al., 2005)
7. Facioscapulohumeral: Onset is from childhood to early adult and includes facial weakness and shoulder weakness (Lovering et al., 2005)
8. Myotonic: Onset is from 20 to 40 years and includes weakness of all muscle groups and delayed relaxation of muscles after contraction (Lovering et al., 2005)
9. Oculopharyngeal: Onset is late at 40-70 years and includes weakening of throat muscles and eyelids (Lovering et al., 2005)

Important Terms

Affordance

An action or behavior provided or permitted for a child by the places, objects and events in an environment ( Haywood & Getchell, 2009).

Contracture

Occurs when a muscle becomes permanently shortened or contracted (Bushby et al., 2009).

DMD

Abbreviation for; Duchenne Muscular Dystrophy.

Scoliosis

The curvature of the spine sideways to compensate for a muscular imbalance (Backhouse & Harding & Hindman & Rodger, 2012).

Lordosis

The trunk is positioned anterior to the hip resulting in an inward curvature of the spine (Backhouse & Harding & Hindman & Rodger, 2012)

Gower's Sign

The use of the child’s arms to climb up their body when moving from a seated position to a standing position (Bushby et al., 2009)

Developmental Progressions and Characteristics in Children with Muscular Dystrophy

Signs and Symptoms

Symptoms vary with the different types of muscular dystrophy. Boys with muscular dystrophy display a progression of muscle weakness and wasting in the larger, proximal muscles and the lower extremities first (MacIntosh & Gardiner & McComas, 2006). Muscle weakness then progresses to the distal muscles and upper extremities (MacIntosh & Gardiner & McComas, 2006)

Indications for Delayed Development

• Delayed development of muscle motor skills (Lovering et al., 2005)
• Difficulty thinking, learning (Lovering et al., 2005)
• Limited fine movements (Lovering et al., 2005)
• Poor balance and coordination (Lovering et al., 2005)
• Difficulty using one or more muscle groups (Lovering et al., 2005)
• Frequent falls due to calf deformation (Lovering et al., 2005)
• Joint contractures of the ankle and hips which cause painful tightening of the muscles and tendons (Elke & Roland, 2013)
• Loss of muscle size (Lovering et al., 2005)
• Delayed ability walking or displays a waddling gait (Elke & Roland, 2013)
• Difficulties with postural control will cause scoliosis or lordosis to develop (Dusing & Harborne, 2010)
• Difficulty getting up from a seated position (Dusing & Harborne, 2010)

Developmental Progression of Muscular Dystrophy

Typical diagnosis of DMD occurs around 2-5 years of age, however, earlier diagnosis can occur due to delayed development of motor milestones such as independent walking or climbing (Bushby et al., 2009). Muscle wasting can be difficult to observe because in some cases, pseudohypertrpohy of the calves occurs from a buildup of fat and connective tissue (Lovering et al., 2005). Wheelchair use typically occurs between the ages of 8-12 and death usually occurs in late teens or early 20s from broncopnemonia or heart failure since cardiac and smooth muscle are also affected in DMD (MacIntosh & Gardiner & McComas, 2006). The development of Becker Muscular Dystrophy resembles DMD however it has a later onset, runs a slower course and is less severe than (Dusing & Harborne, 2010).

Diagnostic Tests

• Physical examination and medical history can be used to determine the type of muscular dystrophy (Bushby et al., 2009).
• A muscle biopsy test can be used to confirm muscular dystrophy when a small piece of muscle tissue is removed and examined (Dusing & Harborne, 2010).
• Genetic testing also provides information to determine if a hereditary disease is causing the problem through a DNA blood test (Bushby et al., 2009).
• A blood test for Creatine Phosphokinase is also a good indicator, as abnormally high levels of the enzyme in the blood usually indicates that there has been stress to muscle tissue, the heart or the brain (Bushby et al., 2009).

In some cases, it is delayed language milestones not motor milestones that are the earliest signs of DMD; therefore, these also need to be observed during diagnosis (Cyrulnik & Fee & DeVivo & Goldstein & Hinton, 2007). Determining how children with DMD present from a cognitive perspective may be the best solution for an early diagnosis and intervention (Cyrulnik et al., 2007).

Canadian Trends and Statistics

• DMD affects 1 in 3,500 boys (Blake & Weir & Newey & Davies, 2002)
• DMD is the 2nd most common genetically inherited disease (Anderson & Head & Morely, 2002)
• There are approximately 23,350 people with Muscular Dystrophy in Canada according to data from 2010-2011 (Statistics Canada, 2011)
• Estimated prevalence rates of the most common forms are 1 in 5,000 male births (Leung & Wagner, 2013)
• Males are more commonly affected by DMD due to a genetic recessive disorder of the X chromosome (Ervasti & Sonneman, 2008)
• Children with DMD have been found to be 40% less active than the general population regardless of age (Backhouse & Harding & Hindman & Rodger, 2012)
• The average age for wheelchair dependency is approximately 10 years with a range of 7-12 years (Dusing & Harborne, 2010)

Concerns for Childhood Motor Development in Children with Muscular Dystrophy

Newell's Model of Constraints

The main concerns for children with muscular dystrophy are made clear in Newell’s model of constraints which combines both the biological and ecological systems perspective (Gabbard, 2009). The model is used for studying the motor development of a child and observes differences in individual, environmental and task constraints (Gabbard, 2009). A movement results from the dynamic interaction between an individual, the task and the environment and will either permit a movement to emerge or restrict a movement from occurring (Gabbard, 2009). Task constraints are external to the body while environmental constraints are global and relate to the world outside the body (Gabbard, 2009). When considering muscular dystrophy, an individual and structural constraint is the abnormal muscular development, which poses problems for movement pattern execution (Bushby et al., 2009). As the disease progresses, there is more physical limitation and an increased sedentary lifestyle which gradually causes secondary physical deterioration aside from the obvious loss of muscular strength (Bushby et al., 2009). In addition, there are functional constraints relating to muscular dystrophy including anxiety and fear, which is exacerbated by cognitive deficits in mental flexibility and adaptability (Bushby et al., 2009).

Developmental Problems in Children with Muscular Dystrophy

Development is the interrelationship between growth and maturation in relation to the passage of time (Long term athlete development, 2011). The rate and extent of development is individually determined and influenced by demands of a task as well as environmental factors (Long term athlete development, 2011). The child’s level of growth, maturity and development that enables them to perform tasks and meet the demands of daily living are known as readiness (Long term athlete development, 2011). Atypical development is common with muscular dystrophy; therefore it is necessary to understand what constitutes a normal range for these children so that appropriate intervention and remediation can be done when there is significant deviation from the expected development timeline (Long term athlete development, 2011).

Concerns for Fundamental Movements

Fundamental movement concepts including balance, agility and coordination are critical for the development of all children and are required to progress towards gross motor skills (Gabbard, 2011). Fundamental movements are gross movements common to daily living and are typically mastered in early childhood (Gabbard, 2011). They are the skills that children need for living and functioning effectively thereby forming the basis for competent movement (Gabbard, 2011). In children with muscular dystrophy there is a delay in the development of motor milestones known as the landmarks in an individual’s motor development (Backhouse & Harding & Hindman & Rodger, 2012). Force production is key for the development of motor milestones but is limited in children with muscular dystrophy due to the deficient integrity of the muscular complex (Backhouse & Harding & Hindman & Rodger, 2012).

How Does Muscular Dystrophy Affect Childhood Movement Experiences

Reflexes

Reflexes are involuntary movement reactions elicited by forms of sensory stimuli such as sounds, light, touch or body position (Haywood & Getchell, 2009). They are key components that need to be established in order for a child to progress from a rudimentary phase of development, to a fundamental movement phase (Haywood & Getchell, 2009). Aside from the loss of muscle fiber integrity, the tendon reflexes are lessened due to replacement of muscle by connective tissue and fat (Bushby et al., 2009). Research by Moody and Dimitrijevic (1964), suggests there is a correlation between the severity of the muscular weakness and the clinical loss of the deep tendon reflexes. When degeneration had advanced to the point where distal muscles were severely affected, the Achilles tendon reflex was absent (Moody & Dimitrijevic, 1964). This poses problems for walking, as there is a tendency for the child to walk on their toes due to the shortened Achilles tendons (Moody & Dimitrijevic, 1964).

Postural Control

The ability to maintain body posture and to move the body voluntarily into a desired position underlies all motor behavior (Gabbard, 2009). Postural control is the ability to detect changes in the body’s center of gravity in relation to base of support (Gabbard, 2009). Posture supports other action systems including locomotion, orientation and manipulative functions (Dusing & Harborne, 2010). Because all interaction with the environment includes some aspects of postural control, children with deficits in postural control such as those with muscular dystrophy are limited in their experiences (Dusing & Harborne, 2010). In addition, postural control is important for the development of sitting as children learn through active touch about surfaces and develop strategies to stabilize the body (Dusing & Harborne, 2010). Highly complex variability of postural control drives change and serves as a foundation for function in the first year of life (Dusing & Harborne, 2010). Limited complexity during development of postural control has been identified in children with muscular dystrophy and is problematic for their exposure to perceptual motor experiences (Dusing & Harborne, 2010).

Sitting

Due to proximal muscle weakness, young boys with muscular dystrophy will have extreme difficulty in their ability to move themselves into a sitting position (Moody & Dimitrijevic, 1964). Gower’s sign is usually a complication of muscular dystrophy and results from proximal weakness of the pelvic girdle muscles (Backhouse & Harding & Hindman & Rodger, 2012) The child must use their hands and arms in order to push their body up into a squatting position due to a lack of hip and thigh strength (Backhouse & Harding & Hindman & Rodger, 2012). This makes is extremely difficult for the child to move into a seated position or rise from the floor without the need to press on their thighs for support (Backhouse & Harding & Hindman & Rodger, 2012).

Walking

During early walking, a child must have enough muscular strength in the trunk and extensor muscles to be able to maintain an upright posture on a small base of support (Gabbard, 2009). Children with muscular dystrophy will always experience a delay in walking, unsteadiness and difficulty in running (Backhouse & Harding & Hindman & Rodger, 2012). The child usually has a waddling gait pattern and difficulty climbing stairs due to weakness of the gluteus muscles, pseudohypertrphy of the calf muscles and proximal limb muscle weakness (Bushby et al., 2009). Those with muscular dystrophy can also have a toe-walking gait pattern due to tightness of the Achilles tendon and weakness of the hip extensors (Elke & Roland, 2013).

Krajewska (1977) observed the motor development in children with Duchennes Muscular Dystrophy and found the affected children started to walk in the 19th month of life. This is significantly different from the general population as most infants are taking their fist steps between 9 and 12 months and walking well by the time they are 14 or 15 months (Krajewska, 1977).

Practical Application: Strategies and Recommendations to Enhance Movement Experiences for Children with Muscular Dystrophy

Non-pharmacologic Strategies

For children with muscular dystrophy, the muscular system acts as a rate limiter that slows the emergence of motor skills (Gabbard, 2009). During development there are a series of systems that will either contribute to the emergence of a motor skill or hinder its development and act as a rate limiter (Gabbard, 2009). These children don’t develop according to chronological age; therefore it is necessary to provide them with appropriate affordances for the basic motor skills to ensure optimal development (Gabbard, 2009). An affordance is the function or opportunity an environmental object, surface, place or event provides to an individual to enhance movement experience and allow optimal development (Haywood & Getchell, 2009).

Types of Exercise for Optimal Development

Resistance exercise used to hypertrophy the wasting muscle is controversial as eccentric exercise imposes the most stress on a muscle due to the lengthening of the muscle fiber (Leung & Wagner, 2013). Resistance training may make the disease worse as efforts to increase muscle strength may be countered by the risk of overuse and excessive breakdown of muscle that already has a limited regenerative capacity (Leung & Wagner, 2013). However, there is evidence to suggest that when an exercise program is done effectively and safely, it can temporarily improve muscle function and enhance walking ability (Leung & Wagner, 2013). Sub maximum aerobic type exercises are recommended, especially in the early course of the disease when residual strength is higher (Bushby et al., 2009). Activities such as bike riding and swinging strengthen gross motor skills while ball games are important to incorporate some sensory development for balance and coordination (Cyrulnik & Fee & DeVivo & Goldstein & Hinton, 2007). Land-based activities that require a lot of running or walking upstairs are quite taxing on the muscles, where as water exercises such as swimming result in minimal muscle damage because gravity is eliminated (Cyrulnik & Fee & DeVivo & Goldstein & Hinton, 2007). Walking becomes very difficult as the disease progresses and falling occurs more frequently, therefore, the child becomes more sedentary causing deformities of the feet to occur (Carroll, 1985).

Tips for the Parent: Minimizing Constraints

Parents of children with muscular dystrophy should minimize their child’s daily environmental and task constraints to allow the child to perform skills more proficiently (Haywood & Getchell, 2009). An individual constraint such as a loss of muscular strength cannot be modified on a daily basis but interactions between the environment and the task can be manipulated to make permanent changes in the individual constraint and facilitate more desired movements (Haywood & Getchell, 2009).

Stretching

A daily routine consisting of moving the joints through their full range with gentle pressure will allow the child to maintain some flexibility and minimize the risk of contractures (Cyrulnik & Fee & DeVivo & Goldstein & Hinton, 2007). Stretching also allows the child to maintain some non-locomotor fundamental movement concepts such as bending and postural control (Bushby et al., 2009). Passive heel-cord stretching exercises need to be done twice daily for at least 5 minutes on each foot (Elke & Roland, 2013). The parent dorsifelxes their child’s foot to the point of slight discomfort and then holds the position for five seconds (Elke & Roland, 2013). The maintenance of a good range of motion and bilateral symmetry are important to allow optimal movement and functional positioning (Bushby et al., 2009).

Affordances in the Home to Enhance Movement Experiences for Children with Muscular Dystrophy

• Orthopedic appliances such as braces allow for the improvement of mobility and prolonged elongation and stretching of a muscle-tendon unit to maintain movement patterns (Bushby et al., 2009).
• Banisters can be used along a staircase to aid in the child’s ability to climb stairs (Carroll, 1985).
• Night splits or ankle-foot orthoses can be used to hold the feet in a desired position to minimize progressive contractures and deformity (Leung & Wagner, 2013).
• Spinal supports can be used to delay the development of scoliosis (Bushby et al., 2009).
• Knee-ankle-foot-orthoses or KAFOs can be used when walking becomes progressively more difficult
• Standing pivot transfers can be used when increased muscle weakness and lower extremity deformities cause frequent falling (Hunt, 1981).
• Wheelchairs can be used in the late stages of DMD to allow children to perform activities of daily living more efficiently.
• In the household environment, appliances such as sinks and countertops can be scaled to the child’s relative seated height to minimize environmental constraint.

Postural Affordances

Postural correction is used to counter muscle weakness, contractures and spinal irregularities that force individuals with muscular dystrophy into uncomfortable positions (Bushby et al., 2009). Parents should ensure their child is sitting upright when appropriate with their feet at a 90-degree angle to the floor (Bushby et al., 2009). Affordances such as pillows and foam wedges can help to keep the child upright and distribute weight evenly to allow the legs to straighten (Bushby et al., 2009). In addition, a plastic thoracic body jacket can be prescribed by the practioner to maintain the spine in a straight position and prevent an early onset of scoliosis (Elke & Roland, 2013). Postural correction is necessary as joint contractures limit joint function and are usually permanent which makes them difficult to overcome (Lovering & Porter & Bloch, 2005).

Tips for the Teacher: Minimizing Constraints

There should be modification of activities during the day and at school that may be harmful to the child’s muscles. These include the activities done during physical education such as track and field as these types of exercises may put too much eccentric stress on the child’s muscles (Bushby et al., 2009). The teacher at school should consider accessibility issues as well as playground activities that may lead to extreme fatigue (Bushby et al., 2009). The teacher should also be aware of rate limiters in the environment and understand ways to manipulate these constraints. A child with muscular dystrophy won’t have the muscular strength to shoot a basketball on a ten-foot goal. However, if a smaller hoop is provided for the child then they can engage in the same activity without any task constraints.

Daily Exercise Prescription for Children with Muscular Dystrophy: Ages 1-6

• Passive heel-cord stretching exercises, 5 second hold for 5 minutes at least once a day (Carroll, 1985)
• Passive stretching of the hips and ilio-tibial bands at least once a day (Carroll, 1985)
• Daily knee range of motion exercises and knee extension positioning is important for preventing knee flexion contractures (Hunt, 1981)
• Aerobic, non weight bearing activities at least 3 times per week for 30 minutes including swimming (Bushby et al., 2009)
• Tricycles and bicycles with training wheels are also good sources of non weight bearing aerobic exercise (Carroll, 1985)
• Power pumpers can also be used and include plastic cars propelled by the children moving their arms forward and back (Carroll, 1985)

It is important to adjust these exercises for the child if it is too difficult so that they can fully participate in the program (Fragala-Pinkham & Haley & Rabin & Kharasch, 2005).

Importance of Exercise

Without any intervention the child will lose their ability to walk and confinement to a wheelchair results in worsened contractures (Elke & Roland, 2013). Fragala-Pinkham et al. (2005) found that children with chronic diseases such as muscular dystrophy are among the least active subgroup of children and are at an additional risk for a variety of health conditions associated with a sedentary lifestyle. Therefore, these exercises are extremely important for enhancing movement experiences as they will not only slow the rate of increased weakness or contracture development but they can strengthen postural muscles, maintain respiratory capacity and prevent weight gain in these children (Wagner & Vignos & Fonow, 1986). In addition, exercise can have positive effects on self-esteem and self-confidence (Fragala-Pinkham et al., 2005).

Safety Concerns

Before preforming any exercise regime, it is necessary for the children to obtain a complete medical evaluation and receive physician consent before beginning an exercise program (Fragala-Pinkham et al., 2005). Safety concerns include cardiac arrhythmias and right and left ventricular dilation which will limit the ability to exercise (Fragala-Pinkham et al., 2005). Parents of the children should report ay problems associated with the exercise including muscle pain or soreness, as these symptoms will only exacerbate the disease (Wagner & Vignos & Fonow, 1986). Safety in the home is extremely important because any unsupervised, excessive activity may be harmful to dystrophic muscle resulting in further unnecessary degeneration of the muscle (Wagner & Vignos & Fonow, 1986). Parents should ensure their child is avoiding an excessive exercise intensity or maximal effort during exercise to avoid muscle damage (Wagner & Vignos & Fonow, 1986).

References

Aartsma-Rus, A.,Van Deutekom, J.C., Fokkema, I.F., Van Ommen, G.J., Den Dunnen, J.T. (2006). Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule. Muscle Nerve, 34(2), 135–44.

Anderson, L.J., Head, I.S., Morely, W.J. (2002). Brain function in duchenne muscular dystrophy. Brain: A Journal of Neurology, 125(1), 4-13

Backhouse, M., Harding, L., Hindman, N., Rodger, S. (2012). Duchenne muscular dystrophy using the sensory profile. British Journal of Occupational Therapy, 6(75), p271

Blake, J.D., Weir, A., Newey, E.S., Davies, E.K. (2002). Function and genetics of dystrophin and dystrophin-related proteins in muscle. American Physiological Society, 82, 291-329

Bushby, K., Finkel, R., Birnkrant, J.D., Case, E.L., Clemens, R.P., Cripe, L.,. . . . Constantin, C. (2009). Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol 2010, 9, 177-89

Carroll, E. J. (1985). Diagnosis and Management of Duchenne Muscular Dsytrophy. Pediatrics in Review, 6(7), 195-200

Cyrulnik, E.S., Fee, J.R., De Vivo, C.D., Goldstein, E., Hinton, J.V. 2007. Delayed developmental language milestones in children with duchenne’s muscular dystrophy. The Journal of Pediatrics, 5(150), 474-478

Dusing, C.S., Harborne, T.R. (2010). Variability in postural control during infancy: Implications for development, assessment, and intervention. Journal of the American Physical Therapy Association, 90, 1838-1849

Elke H., Roland, M.D. (2013). Muscular dystrophy. Pediatrics in Review. 21(7), 233-237

Ervasti, M. J., Sonnemann, J.K. (2008). Biology of the striated muscle dystrophin-glycoprotein complex. International Review of Cytology, 265, 191-225

Fragala-Pinkham, A.M., Haley, M.S., Rabin, J., Kharasch, S.V. (2005). A fitness program for children with disabilities. Journal of the American Physical Therapy Association, 11(85), 82-1200

Gabbard, C. P. (2011). Lifelong Motor Development, 6th Ed. San Franscisco, CA: Pearson Benjamin Cummings.

Gabbard, C.P. (2009). A developmental systems approach to the study of motor development. Texas: Nova Science Publishers, Inc.

Haywood, K., Getchell, N. (2009). Lifespan Motor Development:5th Edition. Human Kinetics.

Hunt, K. Antje. (1981). Use of knee-ankle-foot-orthoses for transfers of nonambulatory boys with duchenne muscular dystrophy. Journal of the American Physical Therapy Association, 1(61), 51

Krajewska, G. (1977). Motor Development in children with muscular dystrophy of the duchenne type. Neurol Neurochir Pol, 11(6), 647-51

Leung, G.D., Wagner, R.K. (2013). Therapeutic advances in muscular dystrophy. Animals of Neurology, 3(74), 404-411

Long Term Athlete Development. (2011). Canadian Sport for Life. Published by Canadian Sport Centers. Editors Sheila Robertson, Ann Hamilton

Lovering, M. R., Porter, C. N., Bloch, J.R. (2005). The muscular dystrophies: From genes to genetics. Journal of the American Physical Therapy Association, 85, 1372-1388

Statistics Canada. (2011). Neurological conditions by age group and sex, household population aged 0 and over. Retrieved from http://www5.statcan.gc.ca/cansim/pick-choisir?lang=eng&p2=33&id=1051300

Wagner, B.M., Vignos, J.P., Fonow, C.D. (1986). Serial isokinetic evaluations used for a patient with scapuloperoneal muscular dystrophy: A case report. Journal of the American Physical Therapy Association, 66, 1110-1113