Biomechanical Analysis of Postural Sway in Elderly Adults on Ramps

This study investigated the effects of ramp angles on postural deviation as a function of age. Five ramp inclinations (1:8, 1:10, 1:12, 1:16, and 1:20) were examined in both ascent and descent directions. Five younger (22 to 28 years) and five older (78 to 88 years) adults participated in the study. Video-based motion analysis was used to measure torso and hip angles while participants walked on an adjustable inclined ramp. Both young and older participants had a significant increase in torso angle across ramp slopes from ascent to descent. In addition, the data indicated that older participants tended to lean to the right while walking while the young participants leaned to the left. Measurements of hip angle revealed that young participants had significantly greater hip movement than older participants and that hip angle decreased significantly as participants transitioned from descent to ascent trials. Based on the data observed, it is possible that ramp descent is more problematic for elderly adults. However, within the ramp conditions evaluated, the data were unable to clearly discriminate between ramp slopes beyond identifying differences between slopes of ascent and descent.


INTRODUCTION
maintain the body's center-of-gravity over the base of support during quiet standing and movement. The ability to maintain As the 21st century has come, there is a need to refine postural control is critical for successful performance of experiments to consider elderly adults. According to Howell nearly every daily task. (1997), nearly 13% of the population is at an age of retirement Falling is one of the most serious problems facing older (i.e., 65 and older). One area of importance for the elderly adults. Falls are the leading cause of accidental death in the population is building access. Access to public buildings is over 65 years age group (Maki, Holliday, and Fernie, 1990). important because it allows the older population to maintain Fear of falling leads to a loss of confidence and reduced independence which promotes a higher quality of life. If a activity, resulting ultimately in a loss of independence (Maki, building entrance is not at street level, access can be provided Holliday, and Topper, 1991). Although falling is a complex in two forms, stairs and ramps. However, stairs could cause and multifactorial problem, there is little doubt that problems for the older adult. For example, the relative loss of deterioration in postural balance is one of the major muscle strength in older adults (Vercruyssen, 1997) might contributing factors (Maki et al., 1990). The decrease in increase their risk of tripping or losing balance on stairs, information from kinesthetic receptors or decrease in the use which consequently increases their risk of falling. One of that information in the central nervous system may also altemative to stairs is a ramp. Ramps are used, not only as a contribute to the higher incidence of falls (Kroemer, 1997). means of access in and out of public buildings, but also to Safe building access is necessary to minimize the risk of falls. provide assistance in transferring between levels within buildings. Single-story buildings with multiple elevations PROBLEM DEFINITION typically provide both stairs and ramps. However, the ramp guidelines supported by the Americans with Disabilities Act The research presented in this paper addresses the issue of Accessibility Guidelines (ADAAG) were designed primarily older adults and their ability to walk on ramps of various for people bound to wheelchairs and may not include the inclinations. Wolf'mbarger (2000) stated that it may be safer ambulatory elderly population, to walk on ramps rather than stairs because walking on ramps Two processes that are the foundation of independent is more closely related to walking on a flat surface. mobility are the control of balance and the ability to integrate 'Consequently, the use of ramps may reduce the risk of trips balance adjustments into ongoing voluntary movements such and missteps (Jackson and Cohen, 1995). The current study as reaching for or lifting objects (Woollacott, 1993).
investigated relationships between postural sway and ramp Secondary to disease processes associated with aging or to the slope. The current ADA guideline of ramp slope (1:12, one aging process itself, balance often becomes impaired as one foot of rise for every 12 feet of run) was examined along with grows older (Hughes, Duncan, Rose, Chandler, and Studenski, four other ramp slopes. The goal of this study was to identify 1996). Numerous authors have defined postural sway as the appropriate ramp slopes for older adults. This was achieved ability to maintain one's balance. Hageman, Leibowitz, and by investigating multiple slopes to identify if a critical slope Blanke (1995) defined postural control as the ability to exists at which balance on ramps becomes impaired.

Experimental Design Participants
The study used a repeated measures design with ramp as a Forty-three participants were recruited from local within subject effect and age as a between subjects effect. churches, University of Oklahoma faculty and students, Five ramp slopes were evaluated: 1)1:20 (2.9°), 2) 1:16 (3.6°), retirement homes, and teaching seminars. Participation in the 3) 1:12 (4.7°), 4) 1:10 (5.7°), and 5) 1:8 (7.1°) in both ascent experiment was a two-step process. First, all elderly and descent directions of travel. These ten combinations were participants completed a questionnaire, to determine examined along with a baseline or flat slope, creating 11 preferences and patterns of use for ramps or stairs unique ramp conditions. Performance was evaluated using (Wolfinbarger and Shehab, 2000). Second, survey measures of torso angle (TA) and hip angle (HA). TA participants who volunteered for the experiment were selected represented leaning of the torso to one side of the vertical axis based on qualification into two age groups. Six participants and was measured as the angle created by the C7 vertebra, the were classified as young (average age = 24.6 years) and six lumbscacral center at the L5/S 1 (vertex), and the y-axis. HA participants were classified as older (average age = 81.8 represented the tilt in the pelvis about the horizontal axis and years), wasmeasured by theanglecreated between thefightposterior hip joint center, left posterior hip joint center, and the x-axis.

Equipment
An adjustable wooden ramp was used as the test Task Procedure instrument. The ramp was 6 ft wide and 16 ft long with an 8 Before the experiment, all participants signed an informed ft inclined section. Several safety features were incorporated: consent form. The older participants were administered the 1) handrails around one side and both ends, 2) padded mats on Mini-Mental State Examination (MMSE) to screen for the floor along the open edge of the ramp, 3) a bright yellow evidence of dementia (which would have lead to removal 12-inch wide strip along the open edge of the ramp, and 4) a from the study). Participants changed into the experimental texturized non-slip additive in the painted surface. In addition clothing and were instrumented with reflective markers for to providing better frictional characteristics, the non-slip video recording. additive helped simulate the feel of a concrete, exterior ramp.
Participants began by familiarizing themselves walking A video based motion analysis system was used to capture on the ramp at an angle of 1:12 (ADA guideline). The data. Two cameras provided views of motion in the sagittal experiment began with the baseline trial (fiat slope). Due to plane and in the frontal plane. The video captured movement the difficulty in changing the direction of incline of the ramp, through the use of reflective markers. Markers were located at all slopes were completed in succession for a given ramp the C7, the right and left tip of the scapula, the L5/S 1, and the direction. For each participant, the order of the ramp right and left posterior center of hip rotation, following condition was counterbalanced to first determine direction of guidelines proposed in Chaffin and Anderson (1984). PEAK travel and then to order the slopes within each direction. Motus (version 4.3.1) software was used to digitize the video Participants performed three trials at each experimental and calculate characteristics of motion. When analyzed, the condition and were given ample opportunity to rest between markers produced the stick figure as shown in Figure 1. trials.

RESULTS AND ANALYSES
To Let_ angle was used to investigate the extent of the torso motion Right Hip Hip Measuresof torsoanglecan be interpretedas surrogate Joint Center loint Center measures of postural instability in that the larger the torso angle, the further the center of gravity is removed from the base of support. Hip angle was also assessed using a single measure of overall maximum hip angle (HAmax). This value may have occurred either above or below the horizontal axis and was primarily used to determine if any noted torso motion could be accounted for by a larger whole-body movement that may also have been evident in hip motion. In other words, hip and determine if it was contained entirely in the torso or was it young participants and only exhibited a small decrease in part of a larger body movement, motion (a change of less than 2°) from the descent to the Table 1 summarizes the results of the analyses of variance ascent trials. Older participants' hip movement remained with a presentation of the significant effects for each measure, fairly steady across the descent and base trials as well as Note that subject (nested within age and gender) and the across the ascent trials. to their gait speed, stride length, and movement patterns. The < ramp by subject interaction indicates that these individual E 4 differences werealsoevidentasdifferences in themannerby = ...... _"_ which the eleven ramp slopes affected participants.
.E 2 The main effect of ramp was significant for both TAmax-m R andHamax. A closerexamination of TAmax-R (as shown _ 0 ....... in Figure 2) suggests that as ramp inclination progressed from a steep ramp descent, through a fiat inclination, and then -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 through a steep ramp ascent, TAmax-R tended to increase Slope (degrees) slightly. This trend is more apparent for the older participants whose values of TAmax-R showed a rather steady but small Figure 2. Maximum Torso Angle-Right by Slope for increase and were substantially larger than that of the younger Young and Older Participants. participants. Younger participants' Tamax-R seemed to increase slightly as the descent became less steep but remained fairly steady across the base and ascent ramp slopes.   1.60 4.26 <.0001 from reaching significance. However, an interestingand apparently age-related phenomenon was noted in the torso HAmax also exhibited a significant ramp effect that can angle data. Older participants consistently exhibited higher be seen in Figure 3. The trend evident for HAmax is opposite values of TAmax-R while younger participants consistently that described for TAmax-R. As ramp slope progressed from exhibited higher values of TAmax-L (see Figure 4). Although a steep ramp descent to a steep ramp ascent, the maximum no biomechanical or functional explanation could be hip angle tended to decrease. This trend was strongest for the determined, the handrail was always located to the right of the young participants whose HAmax decreased by almost 4°. In direction of travel and it was surmised that perhaps older addition, the data indicated that the young participants had participants were unconsciously leaning toward the handrail. rather large hip motions across all trials. Older participants tended to minimize their hip motion much more than the The measure of hip angle was similarly unable to ---_ "-

Young
distinguish between ramp slopes. Although the data showed 6.... ,-_ o,a smaller hip angles for ascent trials, the ramp slopes still tended to group around direction oftravel.Thatis,littledifference l= 4-= _ --'-----..ff _ was evident between descent slopes and little difference was .E_ 2 -___ evident between ascent slopes. The trend for larger hip x __ '_'_ motion during descent trials was probably due to the tendency m to use less control when walking downhill. This tendency 0 ...... , , .-. towards a more "falling" style of gait would tend to suggest -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 that descent trials may cause some level of instability within Slope (degrees) the pelvic region. Walking uphill typically requires greater muscular control which tends to reduce hip motion. Again, Figure 4. Maximum Torso Angle-Left by Slope for Young within the range of ramp slopes examined, there was no and Older Participants. evidence of any particular slope (including the ADA The only measure in which the factor age attained recommendation of 1"12) being substantially more significance was HAmax. As shown in Figure 3 the younger problematic than any of the others. ' If the data are reviewedfrom the perspectiveof overall participants had consistently higher values of hip angle across motion during ramp walking, it is apparent that the general all trials. Initially, it was expected that older participants would exhibit the larger hip angles due to reduced muscle trends hold regardless of participant age. Hip motion is the strength and control capabilities. However, the data suggest primary contributor to body motion when walking on ramps. that older participants may have compensated for these When descending ramps, torso movement tends to play less of a role in overall movement while the influence of hip muscular reductions be walking in a much more controlled movement is stronger. This phenomenon of a "falling" gait manor than did the young participants, style may be more problematic for the older adult. Due to the One effect of interest, but that was not significant for any loss of muscle strength and control in the lower extremities, of the measures, was the ramp by age interaction. It was descent may impose a larger risk of falling. initially hypothesized that an inclination would have a differential effect on age groups, with a larger negative impact However, when ascending ramps, torso movement tends on elderly performance. However, given the magnification of to contribute more and hip movement tends to provide a individual differences and capabilities within the elderly smaller contribution. Gait during ramp ascent requires more population, it was not surprising that the variability between control which may actually be more physically demanding, participants (both within and across age groups) was too particularly for the older adult. However, there is little in the overwhelming, datato suggest thatascentincreasestheriskof falling.
Although beyond the scope of the current study, an DISCUSSION assessment of limits of postural stability would be helpful to understanding the implications of the data. Although the The results of the present study revealed that slope did patterns of change were consistent between age groups, it may have been that there was an underlying age-related change in have some effect on measures of postural sway during a ramp walking task. However, there were no clear trends among the the limits of postural stability such that the older participants different ramp slopes. In addition, the effects of age group were much closer to their stability threshold than the young wereinconsistent, participants.It wouldalsobe interestingto examinethe role The original intent of this study was to examine ramp of age-related visual impairments in ramp walking. Is the slopes in order to determine if a critical slope exists at which reduction of visual perception problematic during ramp there is an increase in postural instability. Examination of the walking and does it lead to an increased risk of falling? In addition, it would be valuable to correlate the current results to results for torso angle indicated that for both age groups, traveling down a ramp was not particularly problematic from the natural compensations in stride length and gait speed the viewpoint of creating a larger instability due to increased during ramp walking. The observed postural changes may be torso movement. However, travel up a ramp did tend to create .caused by other such characteristics of the gait cycle. greater movement in the torso and possibly cause greater Perhaps these additional studies and measures would provide instability in the upper body. Although ramp slope did attain more insight to understanding the stability changes observed significance, the results were unable to discriminate between in this study. ramp slopes in that all descent trials were similar and all ascent trials were similar. In addition, the ADA guideline was indistinguishable from the other ramp slopes within the same direction of travel.