Motor Development

Milestones in Gross Motor Development

Figure X-1. Milestones in gross motor development | Credit: Santrock, J. W. (2011) Child Development (13th ed.) McGraw-Hill

One of the most obvious signs of development in infancy is the baby achieving the various motor milestones. Parents are very proud of these acquisitions and they are a focus of parental conversations about their infants — ‘Billy can sit now’, ‘Helen has just started to crawl’, ‘Jimmy can walk without help’, ‘Rachel loves to climb up stairs’.

The development of motor skills has very important implications for other aspects of development. The ability to act on the world affects all other aspects of development, and each new accomplishment brings with it an increasing degree of independence.

For example, when infants begin to crawl they become independently mobile and one of the major transitions in early development begins. These changes affect emotional and social development, communication, appreciation of heights and an understanding of distance and space (Campos et al., 2000).

Table X-1 charts the sequence of development of various motor milestones during infancy. At birth the infant has a number of well-developed motor skills, which include sucking, looking, grasping, breathing, crying — skills that are vital for survival. However, the general impression of the newborn is one of uncoordinated inability and general weakness.

Movements of the limbs appear jerky and uncoordinated, and it takes a few weeks before infants can lift their head from a prone position. The muscles are clearly unable to support the baby’s weight in order to allow such basic activities as sitting, rolling over or standing. By the end of infancy, around 18 months, all this has changed. The toddler can walk, run, climb, communicate in speech and gesture, and use the two hands in complex coordinated actions.

The questions that a theory of motor development needs to explain include the following:

• Do the early motor activities prepare the way for the more complex voluntary activities that follow, and if so, how do they do it?
• How do new motor patterns (such as pointing, running, speaking, tool use) develop since they appear to be qualitatively different from earlier patterns?

As we shall see, the answers to these questions are complex.

If you look at Table Table X-1 two things will become apparent. First is that the different motor milestones emerge in a regular sequence — sitting with support, sitting unaided, crawling, standing, walking and climbing appear almost always in this order.

The second is that there is a considerable age range in which individual infants achieve each skill — for example, some infants crawl at 5 months while others are as late as 11 months.

These two aspects of motor development give separate support to the two major theories of motor development that we will discuss here — maturational theories and dynamic systems theory.

Maturational theories

One of the first psychologists to investigate human motor development was Arnold Gesell, who studied hundreds of hours of films of motor activity in longitudinal studies of children from birth to 9 years (e.g., Gesell & Ames, 1940). He concluded that motor development proceeded from the global to the specific in two directions. One direction is called the cephalocaudal trend and is from head to foot along the length of the body — that is, control of the head is first, then the arms and trunk, and finally control of the legs.

The other direction of development is what is called the proximodistal trend, which is that motor control is from the centre of the body outwards to more peripheral segments — that is, the head, trunk and pelvic girdle are brought under control before the elbows, wrist, knee and ankle joints, which in turn lead to finer control over hands and fingers.

These two invariant sequences of development, together with the regular sequence with which the motor milestones are achieved, led Gesell to the view that maturation alone shapes motor development — development is controlled by a maturational timetable linked particularly to the central nervous system and also to muscular development. Each animal species has its own sequence, and experience has little, if any, effect on motor development.

One of the first researchers to question Gesell’s hypothesis was Myrtle McGraw (1945). She tested pairs of twins where one member of each pair received enriched motor training (in reaching, climbing stairs and other motor skills) and found that in the trained twin motor development was considerably accelerated when compared with the ‘untrained’ twin.

In addition to McGraw’s findings there are other considerations which suggest that a purely maturational account of motor development can be largely dismissed. Here are just two such considerations.

First, the fact that motor skills develop in a regular sequence does not prove a genetic cause. Consider advanced skills such as learning to play a sport, typing, driving and playing the piano. In these instances we can see an invariant sequence of development, as we progress from simple actions to more complex integrated skilful behaviour, but nobody would suggest that these skills are genetically determined!

Second, a maturational theory does not account for the considerable individual differences in the acquisition of various motor skills.

Clearly, a different theoretical account of motor development is needed, and here we describe one of the most recent of these, known as the dynamic systems theory of motor development.

Dynamic systems theory

What has become apparent is that infants (and children) develop skills in different ways. As an example, there are some infants who simply do not like to crawl and these will often stand and walk before they crawl, indicating that the motor milestones referred to earlier are not set in stone.

Those infants who do crawl will acquire it in their own individual ways — some will shuffle on their bellies before crawling on hands and knees, others will skip the belly-crawling stage, and still other infants will forgo the crawling stage entirely, and after several months of sitting and shuffling may stand and then walk (Adolph & Joh, 2007).

In addition to these observations there are what are called microgenetic studies of motor development in which experimenters observe individual infants or children from the time they first attempt a new skill, such as walking or crawling, until it is performed effortlessly (e.g., Adolph & Tamis-LeMonda, 2014).

From these studies it becomes clear that infants’ acquisition of a new motor skill is much the same as that of adults learning a new motor skillOpens in new window — the beginnings are usually fumbling and poor, there is trial and error learning and great concentration, all gradually leading to the accomplished skilful activity, which then is usually used in the development of yet new motor skills.

According to the dynamic systems theory all new motor development is the result of a dynamic and continual interaction of three major factors:

1. nervous system development;
2. the capabilities and biomechanics of the body;
3. environmental constraints and support (Thelen & Spencer, 1998).

Overview

Despite the apparent appeal of maturational theories of motor development, research over the last 35 years has demonstrated that motor skills are learned, both during infancy and throughout life.

The apparently invariant ordering of the motor milestones is partly dictated by logical necessity—you can’t run before you can walk!—and is not necessarily invariant (you can walk before you can crawl!)

From a consideration of the studies described above it becomes clear that motor development cannot be accounted for by any maturational theory. These and other findings contribute to the ‘emerging view of infants as active participants in their own motor-skill acquisition, in which developmental change is empowered through infants’ everyday problem-solving activities’ (Thelen, 1999, p. 103).

The emphasis on children as active participants in their own development is an essential characteristics of the theoretical views offered by ‘The Giant of Developmental Psychology’, Jean Piaget, whose claim was that children’s ability to act on the world underlies their cognitive development, and we now turn our attention to his views.