AGE-RELATED CHANGES IN THE ABILITY TO CHANGE DIRECTION DURING GAIT

L. Gilchrist
Department of Physical Therapy and Exercise Science
S.U.N.Y. at Buffalo, Buffalo, NY 14214

Presented at the 20th Annual Meeting of the American Society of Biomechanics
Atlanta, Georgia. October 17-19, 1996

INTRODUCTION

The focus of this study was on the ability of individuals to alter their gait path by shifting the plane of progression to one side. Two groups of women were studied to identify any age-related changes in the ability to perform this maneuver.

REVIEW AND THEORY

The ability to alter our intended direction of travel at relatively short notice is essential for full mobility in a complex environment. Stability, always an overriding concern in bipedal gait, is often placed at considerable risk when last-minute adjustments are made to the gait pattern. Such adjustments are required when obstacles suddenly appear (or are recognized). One option is to shift the plane of progression to one side and walk by the obstacle.

Patla and coworkers (1991) have studied the ability to turn the plane of progression by 30 or 60 in young adults. They found that such changes could not be made within one step and that considerable changes in the horizontal ground reaction forces occurred. They did not, however, test any older adults. Chen et al (1994) studied age-related changes in the ability to step over a virtual obstacle. They reported that older individuals were considerably less successful in making the step length adjustments required to avoid the obstacle at short notice. They did not, however, measure the ability to side-step, an alternative strategy for obstacle avoidance.

The purpose of this study was to identify age-related changes in the ability to incorporate a sideways shift of the plane of progression into a comfortable walking pattern. Of specific interest were: 1. Do elderly women accomplish such a shift in the same manner as do young women? 2. Do differences between the two groups seem to place the elderly at a greater risk for falling, either as the transition is made or in the steps immediately following?

METHODS

Sixteen young women (age=27 ± 6 yrs) and 16 older women (age=70 ± 3 yrs) were subjects for this study. The given task was to walk down a 5 m walkway that was divided into three parallel lanes, delineated by brightly coloured tape on the floor. The subjects began each trial at one end of the center lane of the walkway, standing with both feet parallel. At a verbal cue from the investigator they began to walk down the center lane. On their third step a visual cue appeared which instructed the subject to move to the lane on the right, to move to the lane on the left, or to remain in the center lane. Subjects were told that in all cases they were to make any adjustments (i.e. change lanes) as quickly as possible, to continue walking forward to the end of the walkway, and to avoid stepping on any of the lines delineating the three lanes. A trial was complete when the subject reached the end of the walkway.

The three lanes were of identical width based on the feet-together stance width of each subject. The lane width was set as this stance width plus an additional 30%. Three footswitches were taped to each shoe and two infrared light beams were used to calculate the average velocity of the subject. Data collection began just before the subject's first heel strike and lasted for 5 s at a rate of 250 Hz. The appearance of the visual cue occurred 100 ms after the third heel contact.

The subjects performed 64 trials in total. Randomly spaced among these were 9 requiring a move to the right, and 9 requiring a move to the left. The visual cues consisted of the words "Right", "Left" or "Center" appearing in 4 cm high letters on a computer monitor. Trials were identified as either Ipsilateral, Contralateral or No Shift trials; e.g. if the signal appeared when the subject was on their right foot, an ipsilateral shift was to the right side.

A video camera placed at the end of the center lane of the walkway was used to record the subjects' footfalls. From this, the stepping strategies that the subjects used to shift their plane of progression (i.e. to change lanes), as well as the number of times they made an error (stepped on a line), could be discerned.

RESULTS

No subject was able to accomplish either shift within the same walking step as the visual cue. Most accomplished the ipsilateral shift within the next step; for the contralateral shift a 2-step strategy was most common (Table 1).

Table 1: Stepping Strategies
Percentage of trials in which extra steps were used to move from the center lane to a side lane.

Table 2: Average Velocities (m/s)
* = significantly different from the comparable no- shift trials. Age differences were significant for all conditions.

The older women walked with a slower average velocity than did the younger women, using longer stance times and shorter swing times (Table 2).

Analyses of the errors indicate that both groups were more likely to make errors on steps 5 and 6. The older women were more likely than were the young women to make an error on step 6.

To examine the temporal adjustments made to accommodate a shift in the plane of progression, only those trials in which the predominant strategies were used, were considered. For the 1-step ipsilateral strategy 183 trials (69%) were included. For the 2- step contralateral strategy 204 trials (76%) were included. The relative timing changes were similar for both groups (Figure 1). The exception was in the 2- step contralateral strategy: the young women spent less time on the second extra step (step 5) than did the older group.

DISCUSSION

The change in gait path studied here was not large; it involved simply taking a step to one side while continuing forward progression, a maneuver commonly used to avoid an obstacle. Although the direction of the shift was mandated, subjects were given the freedom to choose what stepping pattern and temporal adjustments they would use to accomplish the task.

The findings were consistent with those of Patla et al (1991) in that, for all subjects, no discernible alteration in the movement pattern was possible within the same step in which the visual cue appeared. Despite their slower velocity, the older women tended to choose the same stepping patterns as the young women although they were less consistent in their choice. More specifically, they were less likely to choose a rapid strategy. In a situation where such a change is required to avoid an obstacle, taking additional steps may increase the risk of contacting the obstacle. Chen et al (1994) demonstrated the reduced capacity of older individuals to step over an obstacle, particularly when there is little time available to make adjustments. The current study suggests that their result was not specific to alterations within the plane of progression (step length adjustments), but can be extended to include side-to-side alterations.

Although both groups had difficulty placing the foot accurately for step 5, the older group had difficulty on the subsequent step as well. This has implications for those situations where not only does an obstacle appear, but the options for alternate foot placement are limited. (Consider trying to avoid a large path of ice or pool of water in the center of a relatively narrow path.) Even if an older individual were able to respond rapidly enough to avoid running directly into the obstacle, their decreased ability to precisely place subsequent footfalls may also increase their risk of falling.

REFERENCES

Chen, H.-C..J Gerontol: Med Sci 49(5): M227-M233, 1994.

Patla, A. E.. J Exp Psych 17(3): 603-634, 1991.

Figure 1: Mean Step Times. NS = No shift, IP = Ipsilateral, CL = Contralateral, Y = young, O = older. The visual cue appeared on step 3.