Skeletal alignment

Positioning is important toward developing postural stability, but it is also required for children to participate in daily occupations. When the skeletal system is aligned and children are positioned symmetrically, each side of the body develops adequate muscle strength needed for postural stability. Symmetrical alignment helps children maintain the full range of motion (ROM) for movement. Therefore, symmetrical positioning with head, neck, trunk, and pelvis aligned, allows children to move the arms and legs efficiently, bring the hands to midline to work with objects, and maneuver the legs. Positioning children symmetrically provides physical comfort, reduces fatigue, and promotes stability so that they may engage in occupations such as feeding, dressing, and playing. Thus, one of the first principles of positioning is to make sure that children are symmetrical and well aligned. OT practitioners may use positioning devices to support children in symmetrical positions. Often providing external support helps children maintain a position to perform daily occupations (Figure 17-1).

Typical development

When helping children maintain a position, OT practitioners consider typical development and the many different positions children assume as they interact with their environments. OT practitioners provide a variety of options for positions so that children experience a full range of experiences. For example, OT practitioners understanding typical development realize that infants (between 7 and 10 months) begin to explore their surroundings by crawling. Thus, the OT practitioner provides positioning opportunities that promote the prone-on-extended-arms position and support the infant’s efforts to crawl. Similarly, infants at this age enjoy sitting, and some may require external support to maintain the upright position.

Perception and body awareness

Not only does assuming and maintaining various positions promote motor development, they also stimulate perceptual development and body awareness. For example, moving from the sitting position to the standing position provides children with a different viewpoint, engages the vestibular system, and enhances children’s perception of the surroundings. Each new position provides different opportunities and experiences that help children make sense of their bodies and their environments. Children develop perception and body awareness as they make sense of their position in space and view things from different angles. For example, infants’ early feeding experiences occur while they are in the reclining position, whereas toddlers feed in the upright sitting position, and older children may eat while lying in front of a television.

Changing positions stimulates different sensory experiences. For example, weight bearing on hands provides infants with tactile sensations and experiences that are important for later hand development. Children develop body awareness as they experience proprioceptive feedback from their muscles and joints about where their bodies are in space. As children develop the ability to sit upright, they see things at different angles; they feel different sensations; and they develop a sense of balance, which helps promote postural stability for mobility and functional activity (Figure 17-2).

Postural control for balance and functional activity

Maintaining positions requires postural control, which refers to the ability to sustain the necessary trunk control to use the arms, hands, and legs and efficiently carry out skilled tasks, such as playing, coloring, or feeding. See Box 17-1 for a description of the relationship between stability and mobility. Along with adequate muscle tone and skeletal alignment, children need a sense of balance to maintain postural control. Balance, also referred to as postural stability, refers to the ability to maintain the center of gravity over the base of support. The center of gravity is the point where the total body weight is most evenly distributed over the base of support. The center of gravity is also referred to as the center of mass when it relates to the child’s center of distribution. Children must first sense changes in the center of mass before they are able to respond to these changes. Children respond to changes in balance through righting and equilibrium reactions. Righting reactions are those reactions that bring the body back to midline position and are defined as the maintenance of the proper alignment of the head and trunk in space. For example, righting reactions are present as an infant moves his head upright and vertical when tilted to the side (righting the head on the neck). Another example of righting reactions is when the head, trunk, and pelvis rotate on an axis, as seen in rolling to maintain alignment of the body segments (head, trunk, pelvis). This is observed as infants turn their bodies in alignment to roll toward a toy. An infant develops head righting reactions in the first few months of life in response to visual and vestibular sensory input. Equilibrium reactions help one maintain balance when the body’s center of mass is shifted too far over the base of support. Equilibrium reactions may require the use of the head, trunk, arms, and legs to flex or abduct in order to adjust the body’s center of mass over the base of support to prevent a fall. The maturation of equilibrium reactions occurs in an orderly sequence—prone, supine, sitting, quadruped, and standing—as the infant gains antigravity muscle strength and postural control (Figure 17-3). Equilibrium reactions may also involve subtle changes in muscle tone to maintain position. For example, equilibrium reactions can be observed as a child maintains balance when standing on one foot. This involves subtle adjustments in muscle tone to maintain the upright position. Protective extension reactions occur when the body’s center of mass is shifted too far off the base of support and righting and equilibrium reactions cannot bring the body back to midline. They involve extending an arm or a leg forward to “save face” when the change in balance is so extreme that children feel unable to correct their position to avoid falling. Protective extension can be observed as a child quickly places a hand on the floor to catch himself or herself when pushed off balance suddenly. (Refer to Table 17-1 for a description of the development of postural reactions.)

All movement requires an initial weight shift. The term weight shift refers to the change in the center of mass so that one can move a body part. During a lateral weight shift in the sitting or standing position, the side that accepts the weight will respond with trunk elongation, and the side that is unweighted will respond with trunk shortening. This allows a person to maintain an upright position with the head remaining in proper alignment with the body and avoid falling into gravity during shifts of the body’s center of mass. Children may also initiate cephalo-caudal (head to tail) or caudal-cephalo (tail to head) weight shifts. For example, a cephalo-caudal weight shift is required when initiating movement from the supine position to the prone position. Anterior–posterior weight shifts involve tilting the pelvis. The posterior weight shift is used when moving from the quadruped position to the tall-kneel position.

OT practitioners examine the components of children’s movement so they can determine pieces that may be missing or atypical. Intervention is frequently aimed at helping children perform typical movement.