Kinematic and behavioral analyses of protective stepping strategies and risk for falls among community living older adults

Abstract

Background: Protective stepping evoked by externally applied lateral perturbations reveals balance deficits underlying falls. However, a lack of comprehensive information about the control of different stepping strategies in relation to the magnitude of perturbation limits understanding of balance control in relation to age and fall status. The aim of this study was to investigate different protective stepping strategies and their kinematic and behavioral control characteristics in response to different magnitudes of lateral waist-pulls between older fallers and non-fallers.

Methods: Fifty-two community-dwelling older adults (16 fallers) reacted naturally to maintain balance in response to five magnitudes of lateral waist-pulls. The balance tolerance limit (BTL, waist-pull magnitude where protective steps transitioned from single to multiple steps), first step control characteristics (stepping frequency and counts, spatial-temporal kinematic, and trunk position at landing) of four naturally selected protective step types were compared between fallers and non-fallers at- and above-BTL.

Findings: Fallers took medial-steps most frequently while non-fallers most often took crossover-back-steps. Only non-fallers varied their step count and first step control parameters by step type at the instants of step initiation (onset time) and termination (trunk position), while both groups modulated step execution parameters (single stance duration and step length) by step type. Group differences were generally better demonstrated above-BTL.

Interpretation: Fallers primarily used a biomechanically less effective medial-stepping strategy that may be partially explained by reduced somato-sensation. Fallers did not modulate their step parameters by step type at first step initiation and termination, instances particularly vulnerable to instability, reflecting their limitations in balance control during protective stepping.

Keywords: Balance; Falls; Postural perturbation; Protective stepping.

Fig. 1

Four types of first step protective stepping responses. Rear-view of stick-figures plotted from kinematic data of an older faller. → indicates waist-pull to the right side. The dotted line is the stepping leg. — indicates the leg position behind the other leg.

Fig. 2

Mean step count (standard error). Post-hoc analyses for significant group by step type interactions above- and at-the Balance Tolerance Limit (BTL). Only non-fallers significantly varied their step count for different step types. Significant pair-wise comparisons between step types are indicated for non-fallers by bracketed comparisons. Significant group differences for each step type are shown by symbols between two adjacent bars (e.g., **indicates group comparison for LSS above-BTL). Significant group differences were observed for LSS and CFS above-BTL, and for LSS at-BTL. Symbols for p (or adjusted) values: ** < 0.01, * < 0.05, and ? < 0.10.

Fig. 3

Mean first step onset time (standard error). Post-hoc analyses for significant group by step type interactions above- and at-BTL. Only non-fallers altered their step onset time by step type, with significant pair-wise comparisons between step types indicated by bracketed comparisons. A significant group difference was observed for MS at-BTL. Other notations are the same as in Fig. 2.

Fig. 4

Mean single stance duration (standard error). Post-hoc analyses for significant group by step type interactions above- and at-BTL. Both fallers and non-fallers altered their single stance duration by step type, with significant pair-wise comparisons between step types marked for fallers (gray lines) and non-fallers (black lines). Symbols for p (or adjusted values): **** 0.0001; *** 0.001. Other text and symbol notations are the same as in Fig. 2. A significant group difference was observed for MS at-BTL.

Fig. 5

Mean first step length (standard error). Post-hoc analyses for significant group by step type interactions above- and at-BTL. Both fallers and non-fallers altered their step length by step type, with significant pair-wise comparisons between step types indicated for fallers and non-fallers by bracketed comparisons for each group. Text and symbol notations are the same as in Fig. 4.

Fig. 6

Mean trunk angular position (standard error) relative to the line of gravity at first step landing. Post-hoc analyses for significant group by step type interactions above- and at-BTL. Only non-fallers altered their trunk position by step type, with significant pair-wise comparisons between step types indicated by bracketed comparisons. A significant group difference was observed for CBS and MS above-BTL. Text and symbol notations are the same as in Fig. 4.