GAIT INITIATION IN OLDER ADULTS WITH POSTURAL INSTABILITY

Individuals diagnosed with Parkinson’s disease (PD) and older adults transitioning to frailty are two specific populations of older adults that are highly susceptible to falls, are known to possess significant fear of falling, and demonstrate disturbances in postural stability and gait abnormalities (Kressig et al., 2004, Wolf et al., 2003, Adkin et al., 2003, Morris et al., 2001, Hass et al., 2004). Adults transitioning to frailty can be defined as those persons not meeting the criteria for either frail or vigorous based on Speechley and Tinetti’s (Speechley and Tinetti, 1991) classification scheme of ten attributes of frail or vigorous adults. Using this classification criteria (Speechley and Tinetti, 1991), Kressig et al. (Kressig et al., 2004) observed that the spatial and temporal features of gait in this population are characterized by reduced gait velocity and stride lengths and greater variability (greater standard deviations in spatiotemporal parameters) compared to robust older adults. Similarly, Hass and colleagues (Hass et al., 2004) observed that adults transitioning to frailty produced anticipatory postural adjustments during gait initiation that were smaller and less forceful than those reported previously for older adults (Halliday et al., 1998, Martin et al., 2002). Persons with PD are also known to exhibit performance decrements during both straight line walking and gait initiation. Compared to healthy older adults, these patients demonstrate reduced gait speed, stride length, abnormal force regulation, and excessive variability during locomotion and reduced magnitudes of center of pressure (COP) displacements during gait initiation (Morris et al., 2001, Halliday et al., 1998, Gantchev et al., 1996, Martin et al., 2002). Thus, both of these populations have demonstrable problems with postural stability during locomotion and during transitions between states of equilibrium, such as gait initiation. Gait initiation is a functional task representing one of the first voluntary destabilizing behaviors observed in the development of a locomotor pattern as the whole body center of mass (COM) transitions from a large to small base of support. This task represents a challenge to the postural control system due to the volitional transition from a condition of relatively static stable support to one of continuously unstable posture during locomotion (Jian et al., 1993, Martin et al., 2002, Polcyn et al., 1998, Halliday et al., 1998, Chang and Krebs, 1999) and one that has been shown to be a sensitive indicator of balance dysfunction (Chang and Krebs, 1999). Indeed, gait initiation has been studied to provide insight into dynamic postural control and the changes that occur in the control system with advancing age and disability (Halliday et al., 1998, Martin et al., 2002, Mbourou et al., 2003, Michel and Do, 2002, Patchay et al., 2002, Fiolkowski et al., 2002, Sasaki et al., 2001). Of note, however, is that studies utilizing gait initiation to study postural control have been limited to straight ahead walking. The fact that the effects of changing direction during gait initiation has been given little attention is surprising considering: many older adults report falling when directing motion laterally; impairments in lateral stability are an important aspect of balance dysfunction and falls (Rogers and Mille, 2003) and older adults and patient populations are known to have difficulty turning and moving laterally. Indeed, in persons with PD twenty percent of falls are directed laterally and the predominance of sway abnormalities is observed in the mediolateral direction (Bloem, 2003 and 2004). Further, changing direction during the initiation of gait is a common skill performed daily such as when walking away from the kitchen sink or after selecting groceries from the grocery aisle. To date, multi-directional gait initiation and direct comparisons between transitionally frail older adults and persons with PD, whose postural and locomotor performance are both degraded, have not been performed. We suggest that the examination of differences in postural control within these two fall prone populations during forward and lateral gait initiation is valuable for several reasons. First, acquiring more information regarding postural control during functional tasks in these groups could add to our understanding of dynamic postural stability in fall prone older populations. An understanding of performance during multidirectional gait initiation may provide insight as to why changing direction has been associated with an increased incidence of falls in older adult populations. Second, these direct comparisons would provide valuable information regarding the degradation in postural control that is observed in elderly or diseased populations and could help partition which decrements result from increasing frailty, alone, or from the motor dysfunction associated with neurodegeneration. These two groups have also been observed to have similar gait performance with differences in magnitude in stride length, velocity, and cadence between groups averaging <5%. Thus, differences in the performance during gait initiation may be telling in regards to sequencing of postural and locomotor actions. Last, the observed data will be valuable in identifying important variables of interest to be evaluated for intervention-related changes in postural control over time. Given that gait initiation is a destabilizing activity for older adults and that the COP represents the response of the central nervous system during postural adjustments, the purpose of this study was to examine potential differences in the translation of the COP during gait initiation in older adults transitioning to frailty and those with PD.