It is pleasing to finally write this post, as I have admired the work of French Researcher Christine Assaiante for a long time. Like the genius emanating from the Prague School of Rehabilitation, Assaiante, by investigating how postural control develops in children, has given us the gift of understanding what is important to evolve movement sophistication. You might ask, what does the posture of children have to do with me, and how might this help me to move better?
The answer is simple, understanding the strategy of body-based organisation allows you to perform tasks that challenge you as an organism functionally. The major problem as we exit childhood is that we stop play and exploration, and start to sit a lot. This, along with repetitive specialised activities has far-reaching consequences.
Summary of Research Findings
Intersegmental coordination develops during childhood.
First frame of reference for organisation of balance during locomotion is the pelvis.
Head stabilisation is complex requiring a long time to develop during childhood.
It appears that control of orientation and control of balance both require the trunk as an initial frame of reference involving a development from egocentric (body) to exocentric (spatial) postural control. Within this are 2 important steps;
1. Building a repertoire of postural strategies.
2. Learning to select the most appropriate postural strategy based on anticipation of consequence of the movement to maintain balance control and the efficiency of the task.
“According to their ontogenetic model of balance control, Assaiante and Amblard (1995) assumed that the various balance strategies adopted by children, as well as by adults, involve taking into account two main functional principles of spatial organization. The first concerns the choice of the stable reference frame on which the equilibrium control is based, and the second concerns the gradual mastery of the degrees of freedom of the various body joints.
The choice of the stabilized anatomical segment of reference, as well as the character of coupling between articulations, depends on (a) the dynamic constraints determining the difficulty of a motor task, (b) the environment, and (c) the characteristics of each developmental period.
In many movement activities, the contact with the support surface is intermittent. During locomotion, for example, the lower limbs cannot serve as a stable reference frame for the organization of the whole-body balance. Thus, it is necessary to stabilize, at least one anatomical segment, which then constitutes the reference value around which movements can be built up. The reference frame can be either the pelvis to allow a better control of the center of gravity or the head to allow clear vision and better visual and vestibular processing, or both segments, according to the difficulty ofthe task. Moreover, human stance involves super-imposed modules from the feet to the head, each with its own specific central and peripheral regulation, which can be controlled more or less independently.”
There are 2 possible modes of control;
1. Lock down strategy consists of minimising the number of degrees of freedom to be controlled simultaneously during the movement.
2. Articulated strategy consists of controlling independently a couple of consecutive anatomical segments and requires the mastery of the degrees of freedom of the corresponding joint.
“The various balance strategies also involve taking into account two main functional principles of temporal organization (Assaiante & Amblard,1995). These authors assumed that the stabilized anatomical segment constitutes the origin of the temporal organization of balance control.
Segments are involved in movement in an ascending or descending sequence, depending upon the anatomical segment that serves as the reference frame. For example, on a standing task on a stable support surface, the balance control is organized from the feet to the head, in ascending order.
In contrast, in a more dynamic situation, as walking on a narrow beam, the stabilized reference frame can be the head, as it is the case in adults and in children from 7 years of age onward (Assaiante & Amblard, 1993). Balance control is thus organized from the head to the feet, in descending order. In addition, this multi-segmental control also implies an efficient coordination between posture and movement that can be organized in a feed-forward or a feed-back mode.”
The study of lateral balance control of the upper body segments during locomotion from the beginning of walking to 11months of walking experience showed that the pelvis is the first stable frame of reference around which locomotor balance control can be built up.
In adults the head is stabilised in space during movement activities to allow better visual fixation and vestibular processing, as well as to provide a stable frame of reference around which movement can happen. A good analogy for this type of head control is keeping a video camera still, so that it can capture a steady image. You see this type of control in well balanced athletes and all wild animals. My favourite example is the dynamic interplay between a mountain goat and snow leopard. The movement control, balance and context adaptation is the highest possible because of the sheer difficulty of their environment.
It is not difficult to see why someone who spends a lot of time training in a gym setting begins to de-train movement abilities. The most important training inputs are not being challenged because dynamic movement control is not required in non-locomotor training. There is also very little balance required to run on a treadmill or in using a stepping device. These machines have evolved from a weight-loss indoor perspective and have nothing to do with good movement. The basic challenge of upright human locomotion is taking a step, while keeping the pelvis horizontal with spinal lengthening.
There are 3 important Developmental Phases in Postural Control;
1. 3-6 years of age
Increase in head-trunk stiffness.
Lock-down operation of the head-trunk unit.
2. 7-8 years of age
The head is stabilised in space even when balance difficulty increases.
This improvement is associated with a decrease in the stiffness of head-trunk movements of rotation. This is because the articulations of the head-trunk have increased degrees of freedom.
If we contrast the difference between teenagers and adults, teenagers are more dependent on visual cues than adults.
The head is stabilised in space most of the time.
Postural Orientation therefore has 4 main areas;
1. Maintenance of balance
2. Segmental stabilisation
3. Global body orientation
4. Segmental orientation
In conclusion, Assiante findings support the concept of multiple reference frames:
- Stabilization of the head or stabilization of the pelvis, which operate in a complementary manner or in concert, associated with a lock-down or articulated operation of the body joint to permit the most appropriate temporal organization of balance control during action.
- The first step for children consists of building a repertoire of postural strategies.
- The second step consists of learning to select the most appropriate postural strategy depending on the ability to anticipate on the consequence of the movement in order to maintain balance control and the efficiency of the task.
- Developmental studies involving postural control during various posturo- kinetic tasks suggest that anticipatory control, despite its early emergence, slowly matures during childhood as well as the mastering of timing parameters.
- Precise mastering of timing parameters seems to be one of the key factors of the anticipatory function that reflects the maturation of the CNS.
- Taking into account the complexity of the parameters to control, it is not surprising that the development of postural control continues up to late periods during childhood and adolescence.
- The recent development of fMRI studies should help us to better understand the relations between the late maturational process of the CNS and the late development of postural control, particularly at the periods of transition such as 6-7 years and adolescence.
The above summary reminds us that we need to continue to train proprioception and balance and not be over-reliant on vision to know the body and environment. It is important to practice activities that involve timing and rhythm, and that timing and rhythm can be played with in training settings. Feedback means feeling and knowing and feedforward means anticipation. The foot that is about to strike the ground in running, has already begun to fire the sequence of activation to do with landing and springing. We are sublimely sophisticated organisms, our challenge is to explore the pure potential of brain and nervous system within the infinite possibility of awareness. While this statement is romantic, it is not over-stating our capabilities.