Submitted by: Jeremy Nelson PT
4.0 Standing to Sitting.
Much can be learned about the contributing body segments when observing the stand to sit motion. The body is doing more than just reversing gears from sitting to standing. Now the neuromuscular system is dealing with the acceleration of the COG caused by gravity. This is much different from the acceleration needed to overcome inertia when raising the COG above the BOS.
As a result, a different type of muscle contraction and a new level of coordination are required. The eccentric movement places a greater demand on the extensors muscles. Therefore we get to learn more about the patient’s ability to control the deceleration. Eccentric muscle contractions involve the selective deactivation of motor units and the maximization of other motor units. In this situation there is little room for error and any weakness that exists in the neuromuscular system will be magnified. Poor posture and body segments that are not contributing to the COG BOS relationship will further burden the system resulting in a loss of balance.
Consider the contribution of the thoracic spine. Commonly the thoracic spine presents in varying degrees of kyphosis. The thoracic spine although a firm structure, does contribute mobility to allow for the lumbar spine to remain stable and the cervico-thoracic junction to create a stable foundation for the highly mobile cervical spine. In addition, the mobility of the thoracic spine produces a guiding force contributing to the dynamic stability of the scapulae to support the highly mobile gleno humeral joint. Excess kyphosis of the thoracic spine impacts many of the critical tasks required to complete a smooth lowering of the COG.
First, the center of gravity must be well positioned in the symmetrical base of support. With thoracic kyphosis, immediately the body is compensating for the forward head position, resulting in a weight shift posteriorly. With this force moment already established the typical motion is to begin the stand to sit motion with a flexion of the knees, as the body attempts to keep the center of gravity within the BOS. As the knees continue to flex, the BOS begins to change as the heels lift. As a result the performer begins to lose balance anteriorly and will further compensate by a posterior weight shift to balance the feet. Overwhelmed by the force demands, the quadriceps begins to fatigue, or knees begin to hurt. A hard landing occurs with the falling backwards as the posterior moment accelerates.
The key is to change the thoracic spines capacity to support the required position to control the COG over the BOS. Manual techniques as well as therapeutic exercises can be employed to restore the thoracic spine posture. A complete extension of the thorax and pectorals is often required to return the thoracic spine and reduce or eliminate the forward head posture. Returning the cervical spine and head to their natural position also assists the vestibular system in outputting accurate data to the brain about position in time and space. With posture improved, the change effort is not completed as the goal is to promote the control of and not just capacity to.
The key here is to initiate from the hips using the hip hinge in the standing symmetrical position. The hip hinge was present in the sitting to stand motion and helped explained the different scores for the component. So is the case for the standing to sitting. The scoring includes a range from “needs assist to sit” to “sits safely with minimal use of hands”. Along the way the berg identifies the use of hands and the back of the knees to control the descent as well as the degree of control present. The use of hands and knees is a compensatory strategy to use the extremities to control the position of the COG in the BOS. Without maintaining the COG in the BOS it will be impossible to complete the lowering . This can only be done by first hip hinging to complete the tasks.
There is another way to use the hips and knees to promote the hip hinge. Cueing the patient to reach and touch their knees initiates the hip hinge. How the movement professional progresses the plan of care to improve the standing to sit movement will determine how well this motion is available to the nervous system when performing higher level tasks that will be seen in the proceeding Berg components. The inclusion of different paces of movement, supportive equipment and cueing to produce the optimal learning environment for the nervous system to learn how to control the eccentric motions will be critical in improving the patients’ involvement in life.