Developmental milestones are always a good place to start to understand this transition of skills. The World Health Organization gives guidance for consideration of windows of achievement. As clinicians, we can simply compare the child’s performance to the windows of achievement and ask “what milestones should a child of this age have reached by now?’

Figure 1: Windows of milestone achievement expressed in months

Looking at the figure, hands and knees crawling in typically developing children is achieved at a mean of 8.5 months (Range=5.0-13.9) and walking alone was achieved at a mean of 12.1 months (Range=8-18).^[1]

Gait development in children is dependent on a number of factors including maturation of the central nervous system, adequate motor control, adequate range of motion and muscle strength, appropriate bone structure and intact sensation.^[2] Motor development has been previously viewed as being entirely due to maturation of the nervous system in which the brain and spinal cord change primitive reflexes to voluntary actions. More recent theories have considered maturation as one aspect along side interaction with the environment around them.^[2]

The brain stem and spinal cord are the central pattern generators for basic neural organization and function for locomotion. The central pattern generator organizes the activation and firing sequence of muscles during gait. The course of maturation of the central nervous system progresses in a cephalocaudal manner, or an infant learning to use their upper limbs before their lower limbs ^[3] and contributes to the evolution of mature gait.

What do all these neurological changes actually result in?

Pre walking skills are important building block for a baby to development postural control and antigravity muscle strength. Anti-gravity strength of the hip flexors is built during kicking while laying on their backs, while hip extensor strength and elongation begins from tummy time. The hip and knee extensors are built during rising from kneeling to standing position.^[2] All of these are key for independent ambulation.

Toddler’s gait is less stable and efficient than during childhood or adulthood. They walk with a wide base of support, short step length, high cadence, short swing phase and a high foot lift during swing. All of these postures due to early osseous or muscular development. They don’t develop a reciprocal arm swing but instead walk with a high arm guard or wide swinging arms. They tend to have an irregular cadence and a poor energy efficiency^[3] The instability is due to a higher centre of gravity (often helped with a little pot belly), low muscle to body weight ratio and immaturity of the nervous system and postural control mechanisms. The visual, propricoceptive and vestibular systems work together to bring the centre of gravity back to a more stable position.

Early milestones can tell us a lot about a child and their development. These rapid changes mean a toddler will often trip and fall but tend to follow a typical trajectory to maturity. It is essential to identify typical trajectory that early walkers go through to better understand what stage they are at.

References:

1. Group WMGRS. WHO Motor Development Study: windows of achievement for six gross motor development milestones. Acta Paediatr Suppl. 2006; 450: 86-95.

2. Bly L. Motor skills acquisition in the first year. San Antonio: Pearson, 1994.

3. Sutherland DH, Olshen R, Cooper L and Woo SL. The development of mature gait. J Bone Joint Surg Am. 1980; 62: 336-53.