Development of Walking

OVERVIEW: Gait is a medical term used for walking.  Often, in a pediatric therapeutic environment, there is an emphasis on independent walking. Most parents understandably want to know when and if their child will be able walk. This is most likely because for most people, independent walking translates to increased independence in other areas of life and therefore, decreases the amount that a person will have to rely on others for assistance. As therapists, we must understand the several factors that affect the development of gait and be able to work towards independence when appropriate but also be able to determine when independent walking may not be the most important and functional goal at a given stage of development.

Research has shown that typical walking has 5 major characteristics: stability in stance (when foot is in contact with ground), sufficient foot clearance in swing (when limb is moving through the air), appropriate pre-positioning of the foot for initial contact, adequate step length, and energy conservation.  These characteristics are not present from the moment we take our first steps, which can be anywhere from 9-15 months of age in typical development. They develop over time with growth and maturation. Just as you need prerequisites to advance to higher level courses in college, you need prerequisites to achieve the 5 major characteristics of typical gait.  These prerequisites are adequate motor control and central nervous system maturation, adequate range of motion, appropriate bone structure and composition, and intact sensation (mainly proprioception).  Therefore, in the presence of neuromuscular or musculoskeletal disorders, typical walking may not always be achieved. If all the prerequisites are present, then you should see typical gait, which includes the 5 characteristics listed above, emerge by 3-3.5 years of age.

DEVELOPMENT OF GAIT BY AGE:
Birth to 9 months: During the first few months of life, several things are happening that lead to upright movement.  First, body compostion is changing.  On average, in the first 6 months of life, body fat increases from 12% to 25%.  This increase in fat content makes the infant weaker for a period of time.  In fact, some studies have suggested that larger infants with higher body fat percentage may achieve locomotor milestones later than their smaller friends. As they move towards their first birthday, fat content tends to drop while muscle mass increases and therefore, we see babies getting upright. Second, growth is happening more so in the arms and legs than in the head and trunk. This growth allows the baby to provide a greater resistance against gravity.  Third, the baby is naturally exercising muscles that need to be strong for typical walking.  On their backs, they are kicking which develops antigravity hip flexor strength.  Hip flexors are the big, thick muscles in front of our hips that allow us to pick our leg up and move it forward during walking. On their tummies, they are working out their hip extensors or booty muscles. These muscles work on and off and sometimes with the hip flexors to coordinate smooth walking.  Studies show that antigravity control of movement by these two muscle groups at the hip joint typically develops by 8-9 months of age.  Therefore, the baby may not even be able to stand independently and the hip muscles already know how to control gravitational forces. So, if the baby is moving and growing typically at this point, they are gaining muscle mass, losing fat content, and developing antigravity movement and therefore, postural control.

9 to 15 months: During this time, the baby is weight bearing more and developing independent walking. They are cruising, which develops hip abductor muscles strength.  Hip abductors are the muscles on the outsides of our hips that allow one leg to stay stable while the other one swings throught the air during walking.  Are we starting to see a pattern…development of the hip musculature is an extremely important precursor to typical walking. As therapists, we often go back and address this if independent walking is present but atypical. Also, during this time, increased weight through the legs changes the overall structure and alignment.  Here, the baby’s legs will begin to straighten out from their previously bow-legged shape in infancy.  If they are pulling to stand they are now performing muscle contraction in a closed chain, which means their foot is weight bearing and they are pushing through their hip and knee to achieve upright.  An example of an open chain movement would be kicking where the foot is not in weight bearing.  Closed chain movements create new demands on muscle strength and ability to move against gravity.

18 to 24 months: Now that they child is walking independently, you will see the pattern begin to refine. The base of support will begin to decrease because the hip muscles are learning to stabilize within a smaller range of motion. Also, the legs are growing longer becoming the most rapidly increasing dimension of the body.  This even brings the center of mass of the body lower down the trunk allowing for increased stability. Finally, the child is developing more mature strategies for balance and postural control which may result in a more typical looking walking pattern because it involves the ability to anticipate disturbances in balance rather than only react to them once they have happened.

3 to 3.5 years: If everything has occurred typically up to this point, the structure and angles of joints are maturing in to that of an adults. Balance strategies continue to be refined.  Walking speed normalized for height is consistent with that of adults.

6 to 7 years: By this time, walking is fully mature. Little comparison can be made to an adult pattern.  The center of mass is still slightly higher than an adult and will continue to lower with growth.

As you can see, the development of typical walking begins at birth and continues to evolve over several years during times of rapid growth.