How Healthy Older Adults Enact Lateral Maneuvers While Walking

Abstract

Background: Walking requires frequent maneuvers to navigate changing environments with shifting goals. Humans accomplish maneuvers and simultaneously maintain balance primarily by modulating their foot placement, but a direct trade-off between these two objectives has been proposed. As older adults rely more on foot placement to maintain lateral balance, they may be less able to adequately adapt stepping to perform lateral maneuvers.

Research question: How do older adults adapt stepping to enact lateral lane-change maneuvers, and how do physical and perceived ability influence their task performance?

Methods: Twenty young (21.7 ± 2.6 yrs) and 18 older (71.6 ± 6.0 yrs) adults walked on a motorized treadmill in a virtual environment. Following an audible and visual cue, participants switched between two parallel paths, centered 0.6m apart, to continue walking on their new path. We quantified when participants initiated the maneuver following the cue, as well as their step width, lateral position, and stepping variability ellipses at each maneuver step.

Results: Young and older adults did not differ in when they initiated the maneuver, but participants with lower perceived ability took longer to do so. Young and older adults also did not exhibit differences in step width or lateral positions at any maneuver step, but participants with greater physical ability reached their new path faster. While only older adults exhibited stepping adaptations prior to initiating the maneuver, both groups traded-off stability for maneuverability to enact the lateral maneuver.

Significance: Physical and perceived balance ability, rather than age per se, differentially influenced maneuver task performance. Humans must make decisions related to the task of walking itself and do so based on both physical and perceived factors. Understanding and targeting these interactions may help improve walking performance among older adults.

Keywords: Aging; Balance; Lateral Maneuvers; Perception; Walking.

Figure 1:

A) Participants were instructed to walk on one of two parallel paths projected onto the treadmill, the centers of which were 0.6m apart. They were instructed that, following an audible and visual cue, they were to switch (i.e., maneuver) to the adjacent path. B) A hypothetical example of a maneuver completed in four steps. Following two additional steps after the cue, the walker takes a small preparatory (Prep.) step, a large transition (Trans.) step to the new path, and a final recovery (Rec.) step before returning to straight-ahead walking on their new path. We previously demonstrated that young healthy adults typically utilize such a four-step strategy to perform lateral lane-change maneuvers [14].

Figure 2:

A) Time series of Young Healthy (YH) and Older Healthy (OH) left (z_L; black) and right (z_R; gray) foot placements for transitions cued on a contralateral step relative to the direction of transition [38 of 79 total transitions (48%) for YH; 33 of 70 (47%) for OH]. B) Analogous time series of foot placements for transitions cued on an ipsilateral step relative to the direction of transition [41 of 79 (52%) for YH; 37 of 70 (53%) for OH]. For both (A) and (B), the black dotted lines indicate the onset of the cue to transition. C) Time series of all transitions for both YH and OH plotted with respect to when they initiated the transition, defined as the last step taken on the original path (step 0). All transitions are plotted to appear from left to right. D) Step widths (w) and lateral body positions (z_B) at the preparatory (0), transition (1), and recovery (2) steps for YH and OH participants. The summary boxplots indicate the median, 1^st and 3^rd quartiles, and whiskers extending to 1.5 x interquartile range. Values beyond this range are shown as individual data points. For both w and z_B, differences between Steps were highly significant (both p < 0.001). However, Group differences were not (both p > 0.44).

Figure 3:

A) Correlations between Perceived Ability composite scores and the number of contralateral steps taken following the cue for all maneuvers (top) and those cued on an ipsilateral step (bottom). B) Correlations between Physical Ability composite scores and lateral position (z_B) at the transition (top) and recovery (bottom) steps of the lateral maneuver. Least squares regression lines shown on each plot are for reference only to indicate the direction of each relationship.

Figure 4:

A) Stepping data from Young Healthy (YH) and Older Healthy (OH) participants during the straight walking periods before and after the transition, projected onto the [z_L, z_R] plane. For each group, data were pooled across 8 steps before and 8 steps after each of 4 transitions from each participant. B) Stepping data during the preparatory, transition, and recovery steps from 78 analyzed YH maneuvers and 70 analyzed OH maneuvers projected onto the [z_L, z_R] plane, plotted to appear from left to right. For both (A) and (B), the diagonal dotted lines indicate the initial (z_Bi*) and final (z_Bf*) constant-z_B* (downward sloping) and constant-w* (upward sloping) GEMs, determined from averages of each group. Gray dots indicate individual steps, and the blue (YH) and red (OH) ellipses depict 95% prediction ellipses. C) Prediction ellipse characteristics during straight-ahead walking and at each step of the lane-change maneuver for YH and OH participants: aspect ratio (top), area (center), and orientation (bottom). Error bars indicate ±95% confidence intervals at each step derived from 10,000 bootstrapped samples. Statistically significant group differences (p < 0.05) [31] are indicated by the asterisks (*).