As sensory changes are common in older adults, the reader is referred to additional chapters in this text on peripheral neuropathies (Chapters 32 and 33) and sensory changes in visual (see Chapter 51), somatosensory (see Chapter 49) and vestibular (see Chapters 52 and 58) systems for further evaluation and treatment techniques for these systems that will affect balance.

The information from the various sensory systems is relayed to the CNS and is integrated in several areas including the vestibular nuclei and the cerebellum prior to the generation of appropriate motor responses. Prioritization of use of sensory information for use by the CNS is most likely based on the availability of a particular sensory modality, the task at hand and past experiences (Peterka, 2002). The CNS then generates the appropriate motor responses to maintain upright body posture. Various balance strategies are thought to maintain balance depending on the speed of perturbation and the support surface. Slow, small perturbations on level surfaces result in muscle activity that is sequenced from distal to proximal (ankle strategy), while perturbations that are larger, faster, or on smaller surfaces result in muscle sequences from proximal to distal (hip strategy) (Nashner, 1994). A stepping strategy is used when the perturbations take the center of gravity outside the base of support or limits of stability and is used to recover balance (Nashner, 1994). Older adults frequently switch from an ankle strategy to a hip strategy during different conditions such as walking on slippery surfaces or with smaller, slower perturbations (Horak, 2006). Use of inappropriate balance strategies may contribute to falls in older adults.

There are many other factors that contribute to the ability to maintain an upright posture. First, musculoskeletal constraints must be met. Adequate range of motion (ROM) must be available, especially in crucial joints such as the ankle and hip. Impaired ROM of the neck or painful syndromes in the cervical muscles may lead to an altered representation of trunk and head movement and therefore cause imbalance. The proper generation of neuromuscular force is also essential to developing the appropriate balance strategies. The ability to sequence the muscles appropriately and the timing of the muscle activity are crucial and are sometimes the most difficult to retrain following injury (Horak & Shumway-Cook, 1990). When automatic postural responses are examined, older adults demonstrate slowed onset and reversal in normal distal to proximal sequencing of muscle activation compared with younger adults (Woollacott, 1990). Posture or alignment of bony segments can either assist with the production of the balance responses or make it more difficult to generate balance reactions. Maximizing a patient’s postural alignment can assist in regaining their ability to generate balance responses (Horak & Shumway-Cook, 1990). Although most of our balance reactions occur at a subconscious level, a patient’s cognitive status can influence their ability to generate the balance reactions necessary to maintain an upright posture. If a subject is easily distracted or has slow processing, he or she may not be able to react quickly enough to environmental changes to allow them to stay upright. This may be especially true if there is increased activity in the environment, if the patient is distracted by conversation, or if they are preoccupied (Horak, 2006). Many environmental factors can affect a patient’s ability to maintain balance. Decreased or absent lighting, and soft, pliable surfaces decrease the sensory input available to the patient for spatial orientation. Small children or pets underfoot can cause sudden perturbations and make it difficult for a patient to maintain balance, especially if they already have an increased reaction time. Many classifications of medications, ranging from diuretics to CNS suppressants, can also impair a patient’s ability to balance (WHO, 2007; Kenny et al., 2011) (see Chapter 12).