Monday, July 7, 2014

The Importance of Crawling in Infancy

Eight to 10 months is when babies typically begin to crawl. Crawling is the beginning of independently separating from a caregiver, providing a baby a means in which to explore objects and environment with her own volition and self-directed interest. It is a critically important developmental time in which many different sensory systems within the body are stimulated. When crawling, a baby receives tactile input through the many touch receptors located on the palms of the hands, knees, and lower legs and feet. 

A baby can also experience sensations of hot and cold as it crawls towards a heating duct, woodstove, or a cooler area of the room. Proprioceptors, specialized sensory organs located on nerve endings within the baby’s muscles, tendons, and joints, tells the brain information about the baby’s body positioning and movement changes as it crawls. A baby’s developing visual system is stimulated and challenged while crawling, alternating between near and far point distances. As the baby’s gaze shifts from the floor to objects a few feet away, the eye muscles coordinate with the occipital lobe of the brain (primary visual area) to identify and focus on objects in front of the baby, or a parent on the other side of the room. The visual system is also challenged as it communicates with the vestibular system located within the inner ear in order to maintain focus on an object as the head moves in different directions. One such reflex, the Vestibulo-Ocular reflex stabilizes an image on the retina as the head and eyes rotate sideways. This can be observed when a baby is crawling and turns her head to the left or turns her head to respond or orient to auditory or visual stimuli (a dog walking by, or a toy with lights and sounds).

As the baby turns its head to the side, the semi-circular canals and otoliths in the inner ear detect the rotation and change in head position, triggering cranial nerves to communicate with different eye muscles to rotate the eye in a clockwise or counterclockwise direction, compensating for the rotation of the head. These sensory receptors in the inner ear make up part of the human vestibular system, a very important sensory system that detects a person's head position in space, body orientation, movement, balance, and overall body equilibrium.
Read more about it here.

So how does a baby go from a snuggled, swaddled ball of love to locomotion on all fours? Within a few short months, incredible changes are happening within the skeletal system, muscular system, visual, vestibular, and auditory systems that are building the wide range of skills necessary for crawling. Beginning around 5-6 months, when a baby is lying on its tummy (prone), weight is shifted from the belly to forearms, with occasional pushing up and reaching forward on extended arms.

During this time, shoulder strengthening and pelvic stability continues to develop as an important precursor to reciprocal movement patterns needed for ambulation. Legs begin to come closer together with thighs rolling inward toward a more natural alignment. Between 5-8 months, when lying in prone, a baby begins to lift both legs and arms off the floor, strengthening postural extensor muscles, also enabling a pivot in the superman position. This is when the baby spins in one spot on the floor like a compass and may even move across floor in a linear way without use of hands, knees, and feet.

Different pre-crawling skills are developing when the baby lies on its back (supine). Postural flexion begins as the baby lifts its head independently (5-6 months), bringing hands and feet to its mouth, and beginning to reach for toys with one or both hands. These movements facilitate hip flexion greater than 90 degrees, an important precursor to crawling. During this time, segmental movements are also observed (when the baby can separate left and right leg/arm movements or upper and lower body movements).

By 8 months, it is likely that when lying prone the baby can rotate to sidelying, and move into a seated position. Babies at this age are typically sitting with stability for several minutes without support from a caregiver. This type of dynamic sitting gives the baby enough postural stability to reach in all directions, and by 10 months of age, one can easily move in and out of different seated positions. Moving into a seated position from supine (on back) develops a bit later-typically around 12 months.

Although belly crawling (using both sides of the body simultaneously) may be attempted first, pivoting and backward crawling can be seen as early as seven months. Reciprocal movements usually develop soon after as the baby discovers the most effective mode of forward progression. By 11-12 months, (and sometimes earlier) reciprocal hands and knees crawling is typically established, demonstrated by good trunk flexibility and pelvic rotation. Equilibrium responses (reflexes) to quick changes in body positioning are also fully developed at this time. 

In addition to the important benefits of stimulating the different sensory systems, crawling continues to help develop gross and fine motor skills that are necessary throughout one’s lifetime. The reciprocal movements previously mentioned are further developing the neural pathways in the brain that coordinate the left and right hemispheres of the brain. As these pathways continue to form, reciprocal movements become increasingly coordinated with smooth movements leading to greater physical and mental coordination throughout one’s lifetime.

The several arches that form within the hands within the first few years of life (proximal transverse, distal transverse, and longitudinal arch) are essential for in hand manipulation and coordinated tasks such as handwriting, keyboarding, pinching/squeezing, turning a key, holding handles of tools, or picking up small

As a baby crawls, most of the weight bearing in the hands is on the pinky side of the palm. The pinky and ring fingers typically stabilize the baby’s palm on the floor surface. Whereas the thumb, index, and middle fingers are frequently used for fine precision action, furthering developing the separation of the two sides of the palm, necessary for controlled hand movements. As these muscles (and arches) continue to develop, babies can be observed carrying objects with them as they crawl. This separation of the two sides of the hand continues to represent the power, stabilization, and strength side of the hand (pinky and ring finger side) and the fine motor and manipulation side of the hand (thumb, index, and middle finger) throughout the lifespan.

So go ahead, put that baby down and let them explore their environment from their hands and knees. There is so much important neurological development happening in the central nervous system, the skeletal, muscular, visual, and vestibular systems that is far more important than worrying about the germs being picked up from the ground. Plus, they might even clean your floor for you!

My name is Tamasin Kekic and I am a guest writer for the Pediatric Play blog. I recently completed my level 2 Fieldwork in Pediatrics and School-Based practice with Michelle Bonang, OTR/L. After graduating in May with my Masters in Occupational Therapy, I now look forward to passing my licensing exam this summer and finally beginning my career as an Occupational Therapist!

*Note: Many of the milestones discussed are based on statistical norms, some variation in emerging skill areas is expected. If you are concerned that your child is not meeting established milestones for crawling, speak with your pediatrician or an occupational therapist.

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