Restoration of weight-shifting capacity in patients with postacute stroke: A rehabilitation cohort study

If your doctor and therapists are any good at all they can take this analysis and give you EXACT EXERCISES to strengthen those balance muscles. Or  I suppose you could get weightlifting books and figure it out yourself. But you are paying them for this knowledge so ask them to provide that knowledge. This only referred to 49 references, so your doctor should already know this by heart. Some references go back to the 1980's so there is no excuse possible for your doctor and therapists to not already know this.  Good luck, you'll need it.

Restoration of weight-shifting capacity in patients with postacute stroke: A rehabilitation cohort study

 Stroke is a sudden disruption of the blood flow to the brain caused by ischemia (thrombolic or embolic) or, less frequently, by haemorrhage². Depending on the location of the disruption, different cerebral functions can be disturbed, leading to temporary or permanent disabilities. In the Netherlands approximately 1,75 ‰ (i.e., 28.000 inhabitants) of the total population suffer from a stroke each year and with the ageing of the population this number is expected to increase³. The risk of stroke increases with age, especially in patients older than 64 years, in whom 75% of all cerebrovascular accidents occur⁴. A recent 6 month follow-up cost-effectiveness and resource allocation study in the Netherlands showed that 18% of the patients who had suffered a stroke died in the hospital, 40% were discharged back home, 31% to a nursing home, 9% to a rehabilitation centre, whereas 2% remained in the hospital of admission for the total follow-up period³. A majority of the survivors from stroke suffer from a combination of physical and psychological impairments leading to restrictions in their capacity to perform basic activities of daily living (ADL)⁵. Of all possible sensorimotor consequences of stroke, impaired postural control probably has the greatest impact on ADL independence and gait⁶. It also shows a high correlation with perceived disability⁷ and is responsible for a high incidence of falls as a major health problem in individuals with stroke⁸.
Efferent control of posture 
The term ‘postural control’ is used for the control of the body position in space for purposes of orientation and stability⁹. A body is considered stable, or in balance, at a particular point in time when the center of mass (COM) can be maintained over its base of support (BOS) in both static and dynamic conditions. In dynamic conditions, such as walking, this definition takes into account the momentary velocity of the COM, because of which the COM may be temporarily outside the BOS. The COM is the virtual centre of the total body mass, determined by the weighted average of the COM of all body segments. The BOS in an erect standing position is usually defined as the area under the feet in touch with the ground and the area in between these points of contact¹⁰. During movements of the standing body, the vertical projection of the COM may reach the stability limits, approaching the boundaries of the BOS leading to potential instability. To maintain a stable stance position in the sagittal plane, the COM can be relocated over a fixed BOS by using so-called ‘ankle’ or ‘hip’ strategies^11-13. Ankle strategies are commonly used in reaction to relatively small body


perturbations while standing on a firm support surface. Successful ankle strategies require range of motion in the ankle joints with the feet in a foot flat position as well as sufficient strength in the lower leg muscles acting across the ankles. In the case of external perturbation, a body’s forward motion is decelerated or reversed by a synergy of muscle activity that starts in the calf muscles and ascends through the hamstrings to the paraspinal muscles. A backward motion is counteracted by a similar synergy that starts in the tibialis anterior muscle and ascends through the quadriceps to the abdominal muscles^11-13. Using the ankle strategy, the body behaves as if it were stiff allowing rotation mainly at the ankle joints (‘inverted pendulum’). If the body perturbation is too large or the support surface too soft to generate sufficient vertical ground reactive force for effective use of an ankle strategy, the hip strategy is called into play¹³. A forward motion is then controlled by sequential activation of the abdominal and quadriceps muscles and a backward motion by sequential activation of the paraspinal and hamstring muscles, with the lower leg muscles relatively still, in an attempt to change the configuration of the standing body and bring the COM back over the BOS. If the body perturbation is still too large or the support surface too slippery to generate sufficient horizontal ground reaction forces (shear forces) for effective use of a hip strategy, it becomes necessary to adjust the BOS to the moving COM by taking a step¹⁴. Usually, such a ‘stepping’ strategy is selected much earlier in situations where maintenance of a fixed BOS is not considered a high priority. Moreover, although described as discrete entities, the different strategies may be used simultaneously in various mixtures to maintain postural control in the sagittal plane¹³. Postural control in the frontal

plane differs from sagittal plane balance in that it is usually determined by bipedal stability. As a result, the main mechanism for controlling posture is to shift weight between the legs. This loading and unloading of the legs is primarily controlled by alternating activity of the hip abductors and adductors¹⁵. Only in a situation of (near) single leg stance, ankle mechanisms come into play, analogous to the above mentioned ankle strategy, however, now executed by the ankle invertors and evertors. If these mechanisms fail, a hip strategy and stepping strategy can be used in the frontal plane as well. Hence, maintaining an erect standing posture is by no means a passive activity, not even while standing unperturbed. Depending on the impact of external or internal perturbations, substantial muscle force must be generated at various body levels either for equilibrium reactions to maintain a fixed BOS or for stepping responses to adjust and redefine the BOS.
 Sensory control of posture
Effective postural control requires peripheral input from the visual, somatosensory and vestibular systems to detect the body’s position and movement in space. Each of these senses provides different information based on a different frame of reference¹⁶. The somatosensory system provides static and dynamic proprioceptive as well as exteroceptive information using the physical surround as the ultimate reference frame. The visual system is designed to give static and dynamic (‘optic flow’) information of the body’s position and movement with respect to the visual surround. The vestibulum is essentially a system of accelerometers sensitive to both linear and rotational accelerations in all planes of motion. Because the body is continuously exposed to a constant acceleration force (i.e. gravity), the vestibulum also provides information of the body’s position with regard to the line of gravity. All types of postural information are continuously processed and integrated at the levels of the brainstem, the cerebellum and the cerebrum in order to monitor ongoing body movements, to compare these movements with the actions planned, to detect movement errors and to correct these errors by adjusting the motor output¹⁷. This mode of balance regulation is often referred to as ‘feedback’ control of posture. Basic research has shown that the central nervous system (CNS) is able to shift emphasis between somatosensory, visual and vestibular inputs depending on the availability and validity of sensory information. When the somatosensory and/or visual feedback are manipulated, for instance using the Sensory Organization Test (SOT) of the Neurocom Equitest System¹⁸, healthy adults are still able to maintain standing balance^19-21. Where one sense is not providing optimal or accurate information about the body’s position and movement, the ‘weight’ given to that sense as a source of orientation is temporarily reduced, while the ‘weight’ of other, more accurate senses is increased, a phenomenon sometimes referred to as sensory ‘re-weighting’²². Thus, there is a flexible hierarchy in the CNS between different senses to maintain balance. In the case of pathology, a more systematic shift in the ‘weight’ of the available senses may occur. If, for instance, the somatosensory information from the legs is impaired, the visual and vestibular systems will permanently compensate for this lack of information. As for compensation by the visual system, increased ‘visual dependency’ becomes readily evident when such a patient is deprived of visual information. Consequently, balance problems may easily be masked if only relatively simple balance tasks would be used in clinical assessments, such as standing quietly with the eyes open²³. Unmasking sensory deficits in the control of posture should, therefore, be pursued by challenging the body’s stability using conditions of sensory deprivation or conflict²⁴.

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