CHAPTER 6 GROWTH AND MOTOR DEVELOPMENT DURING INFANCY Li-Chiou Chen and Jane E. Clark Made by Wang Yan

§6.1 INFANT GROWTH §6.2 INFANT MOTOR BEHAVIOR §6.3 REFLEXIVE PERIOD §6.4 REFLEXES:THE BUILDING BLOCKS §6.5 SPONTANEOUS MOVEMENTS §6.6 PREADAPTED PERIOD §6.7 THEORETICAL PERSPECTIVES ON INFANT MOTOR DEVELOPMENT §6.8 MOTOR DEVELOPMENT AFTER THE FIRST YEAR §6.9 SUMMARY

§6.1 INFANT GROWTH

Changes in Body Weight and Length The growth changes during infancy are amazing. In general, boys are heavier and longer than girls during infancy.

The growth of infant can be influenced by many factors, including social, economic, and cultural variables. It is suggested that those who were born with low birthweight and thereafter rapidly gained body weight after infancy had higher rates of cardiovascular disease

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Changes in Body Proportion One of the most noticeable physical features of neonates is their large head size in comparison to the rest of their body. Head circumference is similar across countries.

Head circumference has been commonly used as an indicator of brain development. As the head becomes smaller and the legs grow longer in relation to the total body, the center of gravity of the whole body descends.

Physical Growth and Motor Development Physical growth plays an important role in infants’ motor development. Aspects of growth may influence infants’ motor development in different ways.

§6.2 INFANT MOTOR BEHAVIOR

The newborn infant shows very limited mobility and is highly dependent on others to move in the environment. This transformation in the infant’s motor behavior over the first year is significantly aided by reflexes.

Clark (1994) has identified six periods in motor development: Reflexive Period Preadapted Period Fundamental Motor Skill Period Context-Specific Motor Skill Period Skillful Period Compensation Period

§6.3 REFLEXIVE PERIOD

Both the spontaneous and stereotypical movements represent the characteristic behaviors of the “Reflexive Period”. The Reflexive Period starts from about the 3rd month of gestation when reflexive and spontaneous movements can be observed in the fetus, and lasts until around 2 weeks after birth, when the infant starts to show voluntary movements

Because reflexes are critical building blocks for motor development as well as used to test the integrity of the infant’s nervous system, the reflexes will be discussed in detail in the next section.

§6.4 REFLEXES:THE BUILDING BLOCKS

Reflexes are stereotypical, involuntary motor responses to specific external stimuli. Healthy full-term neonates are born with a collection of reflexes that ensure their survival.

Some reflexes, often referred as infantile reflexes, become weaker and gradually disappear after the infant gains the ability to voluntarily control her movements. Some reflexes do not disappear and last longer or exist through the life span, like tendon reflex.

Infantile reflexes can be categorized into two types primitive reflexes rooting reflex sucking reflex Moro reflex palmar grasp reflex foot grasp reflex Babinski reflex asymmetric tonic neck reflex, ATNR symmetric tonic neck reflex, STNR

postural reflexes walking reflex swimming reflex neck righting reflex body righting reflex labyrinthine righting reflex linear acceleration reflexes parachuting reflexes

Function of Infantile Reflexes one of the important functions of infantile reflexes is for survival and protection For infants with very limited mobility, infantile reflexes also function as opening a dialogue for the infant to the external world.

Appearance and Disappearance of Infantile Reflexes infantile reflexes appear and disappear in a certain sequence and, on average, around the same age in typically developing infants.

Any absence or prolonged existence of an infantile reflex is usually associated with pathological conditions in the central nervous system (CNS). neuromaturation theory dynamic systems perspective

§6.5 SPONTANEOUS MOVEMENTS

Neonates most often exhibit spontaneous movements Because of the relatively invariant movement patterns, infants’ spontaneous movements are often called as stereotypies.

One of the most common and earliest spontaneous movements of young infants is leg kicking. Arm waving, with or without an object, is another frequently observed spontaneous movement in early infancy.

§6.6 PREADAPTED PERIOD

Sensorimotor Control of Posture Postural control involves continuous and dynamic interactions between the neuromuscular system and the sensory system (Horak & Macpherson, 1996).

The Preadapted Period of motor development begins with the onset of voluntary movements and spans the first year of life. In the Preadapted Period, the infant develops motor skills that are precursors for later motor behaviors and are species-typical (phylogenetic).

Although motor development is influenced by multiple sources of constraints, biological constraints play a very important role during the Preadapted Period and only a little specific environmental support is required. motor milestones

The acquisition of infants’ basic motor skills can be generally categorized into three groups. postural control locomotion, manual control.

Postural Development in Infants Postural control refers to the person’s ability to maintain the body’s equilibrium and to assume a desired orientation of the body to the environment (Horak & Macpherson, 1996). Head and upper trunk control

Rolling Rolling the body from one position to another requires a certain level of coordination between the two major segments of the body, the head and trunk, and the two sets of limbs, arms and legs.

Sitting Sitting is the first acquired upright posture in humans. Standing Standing on two feet is a significant milestone in the first year of life as it is fundamental to many later appearing motor skills, such as walking and jumping.

Locomotion Development in Infants Crawling Walking

§6.7 THEORETICAL PERSPECTIVES ON INFANT MOTOR DEVELOPMENT

The development of infants’ motor skills follows a fairly consistent sequence. Most infants develop motor skills in the same order and at approximately the same age.

Not every infant develops in the same way or at the same rate. The development of infants’ motor control is an emerging, not pre-wired, process that is influenced by multiple factors. The emergence of new motor behaviors is a dynamic, self-organizing process of the interacting constraints of the organism, environment, and task.

§6.8 MOTOR DEVELOPMENT AFTER THE FIRST YEAR

Once the infant acquires the motor skills of independent walking and self-feeding, she enters into a new period of motor development, called the Fundamental Pattern Period (Clark & Metcalfe, 2002) or the Fundamental Motor Skills Period (Clark, 1994).

§6.9 SUMMARY

Infancy is a period of time when dramatic changes in physical growth and motor behaviors can both be observed. Infancy can be divided into three periods: Reflexive, Preadapted, and Fundamental Pattern Period.

Although individual differences may exist due to cultural or environmental factors, the general developmental direction and sequence of behaviors observed during infancy are relatively consistent and universal.

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