Seating has almost always been thought of as "sitting" and "sitting" in a particular, optimal position. Developing a seating system for any individual, in the past, has been thought to be a plan for optimal support for a seated posture. However, seating for task performance, is very different. Seating for task performance is a range of mobility needed by the body while in a generally stable, seated posture. Seating for task performance is not a single position, but rather an active repertoire and range of seated postures which the body requires in order to allow the mind to think, the eyes to read, and the head, arms and hands to work.

Seating for task performance requires of us new skills in providing seating which works. Seating for task performance must take into account the individual’s current preferences for specific body patterns of movement, their dominant side, and their experience with pelvic weight bearing. These postures are not learned, but are postures inherently known to all members of our species. They are "recognized" by the brain and body, as soon as they are obtained, and become ready for use immediately. They then become a part of the anticipation and preparation to perform tasks, and allow tasks to be performed adequately.

For any isolation and adequate use of an extremity in a graded, controlled movement (for accurate and competent use in task completion), pelvic stability with pelvic weight-bearing must occur and be controlled by the individual herself. This stability of the pelvis is not a position of immobility but rather a position which allows a range of controlled (limited, graded) pelvic mobility.

Pelvic stability is a position of actively "holding still" rather than "passively" restricted. Pelvic stability is not a position of relaxation nor of stillness but a position of "co-activation" or an "active" holding. In short, the body must allow related muscles to lengthen, and to shorten simultaneously. The muscles providing the foundation to the needed isolated movement have to lengthen (or shorten) and hold, while the more active, direct muscle must move, shortening and lengthenin within the needed range. This coordination of active holding to allow more active movement is critical to extremity control.

This pelvic posture is not simply a musculoskeletal posture, but rather a movement of the body, which includes an on-going interaction of numerous systems including: the musculoskeletal, neuromuscular, circulatory, respiratory, gastrointestinal, and endocrinological systems. These physiological systems become integrated, facilitated, and then can be used and developed with experience. This experience is specifically, identified for a particular task and its performance.

Pelvic girdle stability is required for shoulder girdle mobility. This relationship is not learned but is rather an inherent human characteristic, just as the number of body parts are unique to humans. However, this relationship is critically related to weight-bearing and movement. It is pelvic girdle stability combined with shoulder girdle mobility which provides a foundation from which the head can be controlled and moved. This same relationship also allows the upper extremities to be controlled.

When individuals are not mobile, they have little active experience with gravity. These individuals (especially those with hypertonicity), in their current seating systems are most often asked to remain even more "stable" by "not moving." These individuals, then subsequently, and not surprisingly, have difficulty learning how to integrate various sensory-motor skills, especially eye/hand/head coordination. In fact, in restricted ("static" symmetrical) seated postures, those which do not allow for pelvic stability, do not allow the individual to use their head nor hands adequately to perform a task.

Generally, a seated position for task performance is one where an individual's shoulders and head are in front of her pelvis, rather than in line with the pelvis or behind the pelvis. Feet are on the floor, and are weight bearing, and are not symmetrically placed. A knee may be lower than a hip in alignment and one may be higher than the other (in line with the hip). The knees are used and held at a posture of less than 90 degrees of flexion, placed "below" or "under" the body. Weight bearing is not symmetrical, and both hamstrings and quadriceps musculature are co-active. This posture could be described as the posture used to get up out of a chair, but without getting up. (Leading with the head, the pelvis in an anterior tilt, the legs weight bearing, and the shoulder girdle in front of the pelvis.) As experience with this posture is gained, movement is able to be initiated, maintained and replicated as a task or routine would suggest.

In contrast, individuals with increased tone are often seated in a reclined posture, with a wedged, or "anti-thrust" seat (placing the knees higher than the hips, decreasing the hip angle to less than 90 degrees, and forcing the pelvis into a static posterior tilt). Their feet are off the floor and raised onto footplates smaller than their feet. Their lower extremities are placed in symmetry, abducted, usually placing the knees at a position, wider than the hips, rather than in line with the hips. The knees are located at a position of more than 90 degrees of flexion, although their feet may be parallel to the floor. This posture prevents any weight bearing on the thighs, nor the feet, and does not allow the pelvis to anteriorly tilt. In fact, the lower extremities are not allowed to be placed in line with the hips, and are certainly not allowed to touch each other.

Why does this matter? In human beings (our species on planet earth) within earth's gravity, body control is interpreted and performed when the body understands its relationship to that gravity, primarily through the activation of the vestibular system. The ability to weight bear (interpreted through motor proprioceptors), and to stably, yet dynamically react to gravity is critical to our every movement. In fact, the movement of the pelvic girdle (the shift of the pelvis into an anterior posture, and the subsequent active weight-bearing in the lower extremities) is also an "alerting" reaction to the musculoskeletal system. If a human being wants to perform a task, the pelvis must shift, sending messages to both the shoulder girdle and to the head, that gravity is supporting the activity, and the body is ready to work. This shift of the pelvis forward also requires more power from the body, and asks the body to "kick in tone" in extension. This trunk extension, lends additional power to the pelvis for increased stability, to the lower extremities for weight bearing, and to the shoulder girdle and head for movement.

In short, the pelvis and its movement signal the entire body to become ready to perform a task, by encouraging an increase in tone, in power, and in alertness.

Consequently, when an individual needs to learn a new task a learning position (task performance) needs to be assumed. Once this position has been obtained, access can more easily be assumed, and practiced and obtained. For individuals who cannot obtain this posture, seating must be developed to assist them in assuming it.

For example, consider a young child with athetoid cerebral palsy, especially with lower tone in the trunk and higher tone exhibited in the extremities. In her current seating system her trunk and lower body were completely supported by using a tall back, a wedged (anti-thrust) seat, foot straps at both heels and toes, a separate chest "Butterfly" strap, and a large head support. She could not see a hand switch, and she could not use a full set of head switches, as she was weight bearing primarily on her headpiece. As she attempted to reach a switch, her pelvis would thrust posteriorly, she would attempt to push on her legs and feet, and her arms would fly up. She was seen as "having too much thrust, too much tone, and inconsistent with switch access." Why? As she asked her body for increased power, and attempted to move her pelvis, the only place it could go was posteriorly due to her seated posture. This power or increased tone, rather than being used to help her head and hands, "banged" against the head piece and footplates, further trapping her within her seating system. The more she worked, the more tone she required, the more "banging" and extensor tone occurred, and success at reaching a switch was impossible.

However, when her seating was changed to allow her to perform a task, her tone was able to actually provide adequate power for real task use. The seating was changed by first placing her into a carved, firm seat, with deep thigh channels (this provided her legs with tactile/kinesthetic input). The seat itself was placed in a very subtle anterior tilt. The footplates were lowered to simply graze the bottom of the feet. The back was replaced with one of shoulder height. Deeper trunk positioners, close to the trunk were added, not curved (but rather simply available to be present as a cue to her trunk, and deep enough to be present when she would bring her trunk forward. The chest strap was removed, as well as the headpiece. Velfoam straps were added in a simple posture, around the knees and in front of them.

This seating allowed some containment of the pelvis, support at the knees, and prevented her from pushing off of the footplates when back extension was initiated for head control. Trunk support existed but was not constricting. She was now able to move, and see. She had more control of her body, and was ready for the task. She did not use a head support. In fact, head control, was evident, whereas previously, it appeared to be questionable.

This position was originally developed in the belief that when the hips, knees, and ankles could all be placed at a 90 degree posture, placing the body in a mid-line posture. It was presumed that this totally symmetrical posture, would provide head control, control of tone, and would be an optimal seated posture.

This posture will temporarily, change tone. It places the individual in a rested posture, not allowing for any activity. However, we want task performance, consequently movement, and tone are needed. This posture is simply a symmetrical posture, it is adequate for passive and safe sitting, for transportation, or being fed, but it does not allow for independent control to occur. It only appears to be "sound" when thinking of the body as an anatomical "bag of bones." However, it has little to do with any understanding of the neurophysiology of the body and how it must move and work to perform a task.

It is trouble for several more reasons, also. It is too restrictive. To maintain an individual in this posture, especially one who has increased or varying tone, the individual must have a multitude of straps holding them in place. Using straps does not permit the body to learn how to move. Restriction only assists in preventing movement, or paradoxically, due to the "strapping" the body learns to "fight" the system, adding more power directly at the point of the strapping .

If an individual has a body with a low tone trunk, and the trunk positioners and chest strap are added to surround the body, the body will collapse into the straps. The larger and tighter the strap, the more the body will collapse.

First of all, seating for task performance is not a seated posture to be maintained all day, or for long periods. A task performance position is one which must be able to be assumed, maintained, and then moved from as it relates to a particular task being performed. In short, seating has to allow a change in postures. This can best be developed with the use of a tilt-in-space function as well as more adequate and less restrictive seating. We must stop managing tone by stopping it, and instead assist individuals in controlling tone with task.

Starting with the head as the first extremity to control has worked well. Providing a task performance position with the seating, and a tilt-in-space function, can then allow an individual to use a head switch for controlling power, or a device. As the individual works for short periods of time at the activity, (less than 10 minutes) the seating can be observed and assessed as to its truly supportive value to that individual. The individual must be able to move, but by controlling the movement. This control is learned, through practice, and through repeating an activity which is enjoyed.

Most often, with young children, or with inexperienced adolescents or adults, I have found that controlling powered mobility with head access, can provide an excellent foundation for all other access. With a powered system, the seating can be changed without changing the seat the individual is already extremely familiar. The seating for the power can be adjusted for task performance, the chair can be programmed for head access, and it becomes very obvious while observing the individual, what seating changes (while performing this task) need to be made where. For example, if the seat is too anteriorly tilted, the individual will lose trunk control. If the lower extremities kick out, or show increased tone, or move into adduction, the pelvis is not adequately stable. If the trunk collapses, the anterior support is not enough. If the pelvis and trunk are full of extension, and feet are being pushed against the footplates, temporarily remove them.

All individuals, on this planet earth, of this species, already carry the knowledge of the task performance posture with them. It is a human posture, woven into the past evolution and use of our bodies, housed in the mid-brain’s memory bank. We, actually, do not learn this posture, it becomes a part of us, and reveals itself over time, increasingly. However, those of us who are now placed within a wheeled chair, have great difficulty without experience of weight bearing, finding that posture. That’s why, those of us, here to help, must better understand how a body without adequate weight bearing works, and yet provide systems which will allow weight bearing, and pelvic stability and mobility to occur. With that, tasks can be performed, and independence attained.

If you are interested in further discussion, please feel free to contact me, I am also hoping to have a full book ready on this topic, and others regarding seating within this year, 2002.