Balance is the ability to maintain your center of gravity over your base of support; it is often severely affected following a stroke. The ability to regain functional motor skills and increase the intensity of exercise and practice in rehabilitation centers around the acquisition of balance. Although there are many different types of exercise available, some are more likely to improve balance and prevent falls than others. Overall, it appears that balancing mechanisms are very specific to the action being performed, the purpose of the action (the task), and the environment in which it takes place (Carr & Shepherd, 2011).
Practicing balance exercises while standing, along with exercises for lower extremity muscles performed while standing against body weight resistance, is the optimal way to improve balance as well as flexibility, strength and endurance, and fitness. Exercises can include standing up and sitting down, step-ups, heels raises, marching, stair walking, semi-squats, and reaching to the floor sideways and forward to pick up an object. These exercises should be performed with increasing numbers of repetitions and without reliance on the upper limbs for support and balance. Exercises can be made more challenging by increasing the height of steps and chairs and by increasing and varying speed (Carr & Shepherd, 2011).
Balance and functional mobility can be effectively assessed using an assessment tool such as the Berg Balance Scale. This tool consists of 14 tasks, scored from 0 to 56, that assess a variety of functional, balance, and gait activities. Each task is scored on a 1–4 scale; a score of 0 indicates an inability to perform the task while a score of 4 means the patient is independent with that task. The Berg Balance Scale has excellent internal consistency and good test/retest reliability and requires little specialized training. It can be performed with minimal equipment in a small space and can be used in any clinical setting.
Although there are many different types of exercise available, some are more likely to improve balance and prevent falls than others, and overall it appears that balancing mechanisms are very specific to the action being performed, the purpose of the action (the task), and the environment in which it takes place (Carr & Shepherd, 2011).
Sensory Organization for Balance
Of the many systems and organs that provide sensory input to the central nervous system, the somatosensory, visual, and vestibular systems are the ones most directly involved with balance. Understanding how these sensory systems malfunction helps explain the profound difficulties patients have with balance and mobility following a stroke.
The sensory system receives input from the environment through specialized receptors located in the sensory end-organs in the eyes, vestibular apparatus of the inner ear, muscle spindles, Golgi tendon organs, and touch receptors in the skin. Sensory input provides a continuous flow of information to the central nervous system, which in turn utilizes this incoming information to make decisions about movement. The central nervous system sifts, compares, weighs, stores, and processes sensory input and uses this information to alter the force, speed, and range of motion.
The somatosensory system (touch and proprioception) has perhaps the strongest influence on balance. Somatosensory input from touch, heat, cold, pressure, joint position, muscle stretch, and pain, among others, is continuously fed to the brain. There the sensory information is automatically processed and used to make the many quick adjustments that keep us balanced. Somatosensory input provides us with critical feedback about our position in space, body sway, and changes in terrain. This allows our muscles to make constant, automatic adjustments to maintain balance and avoid falls.
The visual system is another key contributor to balance. It allows us to determine the movement of objects in our environment; it tells us where we are in relation to parts of our own body and to other objects. Our visual system does this using both central and peripheral vision. Central vision is processed mostly through the macula—the part of the retina that allows us to see clearly. Peripheral vision provides information to the brain about general spatial orientation and is more important for postural control and balance than central vision. Vision works in conjunction with the vestibular system, comparing information about velocity and rotation with actual visual information (Shumway-Cook & Woollacott, 2012).
The vestibular system is responsible for processing information about movement in relation to gravity—specifically, rotation, acceleration/deceleration, and head stabilization during gait. The vestibular system works with the visual and somatosensory systems to help us maintain our orientation in space; it works with the visual system to stabilize the eyes and maintain posture during walking (vestibulo-ocular reflex). Vestibular disorders cause a feeling of dizziness and unsteadiness and affect the ability of the nervous system to mediate inter-sensory conflicts.
The vestibular system declines with age, and there may be as much as a 40% loss of vestibular nerve and hair cells by age 70. Vestibular decline has a profound effect on balance and postural control. This is because it is used as a reference system by the visual and somatosensory systems when those systems are in conflict. Vestibular impairment can lead to problems with gaze stabilization, blurred vision, and vertigo (Shumway-Cook & Woollacott, 2012).
The loss or disruption of sensory input in the visual, vestibular, or somatosensory systems can affect balance in a number of ways. How balance is affected depends on several factors, including the extent of the nervous system damage, the number and extent of sensory losses, and the availability of the other senses for compensation. In many instances, more than one sensory system is impaired, as in the case of a person with a peripheral neuropathy and visual impairment (common with diabetes and stroke). But, just as an individual with impaired vision develops a keener sense of hearing, a person with a sensory loss will attempt to compensate by using the unaffected or less-affected senses to improve balance.
Even in an undamaged nervous system, our sensory organs don’t always provide accurate information to our brains. We’ve all had the experience of being stopped at a stoplight and having the car next to us start to move—we think we are moving and slam on the brake. As soon as your foot touches the brake you instantly know that you aren’t moving and even feel a little foolish. This is an example of a sensory conflict—the brain gives preference to visual input for a split second—momentarily overriding somatosensory input. In this case, the sensory conflict is quickly resolved, thanks to the somatosensory and vestibular systems. The touch of your foot on the brake along with position receptors in your back and legs quickly tell you that you are, in fact, sitting still. At the same time the hair cells in the vestibular system let you know that there is no forward motion.
Improper Sensory Weighting
Sensory loss may lead to inflexible or improper sensory weighting. A person may depend on one particular sense for postural control even if that sense leads to further instability (Shumway-Cook & Woollacott, 2012). You may notice a person walking with head down, carefully watching every step. In this case, vision has become the dominant sense being used for balance. Retraining would involve improving the use of somatosensory and vestibular input to reduce dependence on visual input. The visual and vestibular systems may be affected, causing visual disorientation and vertigo.
Sensory Disruption and Loss
Sensory disruption—blurred vision, intermittent numbness, pain, and pressure from swelling—can have a profoundly negative effect on balance and postural control. How (and how much) balance is affected depends on several factors, including the extent of the nervous system damage, the number and extent of sensory losses, and the ability of the other senses to compensate for the damage. If more than one sensory system is impaired—as occurs with a stroke—it may be difficult to compensate for sensory losses.
The nervous system has a powerful ability to compensate for actual or perceived disabilities. Once an injury has occurred, the nervous system immediately goes to work attempting to compensate for neurologic changes, weakness, and loss of function. As mentioned earlier, the goal of therapy is to help the nervous system develop strategies and compensations that minimize musculoskeletal damage and maximize function.
Stroke and Fall Rate
Balance difficulties and falls are two of the serious medical complications associated with a stroke. Most people who have had a stroke (75%) fall during the first 6 months post stroke compared with a 30% annual fall rate in the general older adult population (Schmid et al., 2010).
Falls are an important issue during the acute stay, and fall prevention should be addressed immediately following a stroke. For stroke patients, there is an increased fall risk during acute hospitalization. Falls and other medical complications are associated with triple the length of the acute hospital stay (Schmid et al., 2010).
Stroke severity, specifically a National Institutes of Health Stroke Scale (NIHSS) score ≥8, can be used to identify stroke patients who are at greatest risk of falling. Those determined to be at risk for falls should have a fall prevention program initiated while they are still in the acute inpatient hospitalization period (Schmid et al., 2010).
In a recent Canadian study, a lower score on the Berg Balance Scale was associated with greater falls for both stroke and control groups. Researchers found that people recently discharged from rehabilitation to home were at high risk for falls in their home. This may be because, following a stroke, people spend more time at home or are more cautious when outside their home. This finding reinforces the importance of a home assessment, home safety education, and environmental modifications as part of discharge planning (Simpson, 2011).