Healthy older adults generate transverse-plane momenta required for 90° turns while walking during the same phases of gait as used in straight-line gait

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Healthy older adults generate transverse-plane momenta required for 90° turns while walking during the same phases of gait as used in straight-line gait

• Mitchell Tillman,
• Jun Ming Liu,
• Zahava M. Hirsch,
• Janine Molino &
• Antonia M. Zaferiou 

Journal of NeuroEngineering and Rehabilitation volume 21, Article number: 145 (2024) Cite this article

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Abstract

Background

Generation and regulation (control) of linear and angular momentum is a challenge during turning while walking which may be exacerbated by age-related changes. In healthy older adults, little is known about how momentum is controlled during turns, especially within each phase of gait. Each phase of gait affords unique mechanical contexts to control momenta and regulate balance. In healthy young adults, we found that the transverse-plane linear and angular momenta generation strategies observed within specific phases of gait during straight-line gait were also used during turns. Therefore, in this study, we investigated whether healthy older adults shared similar momentum control strategies specific to each gait phase during straight-line gait and turns.

Methods

Nine healthy older adults completed straight-line gait and 90° leftward walking turns. We compared the change in transverse-plane whole-body linear and angular momentum across gait phases (left and right single and double support). We also compared the average leftward force and transverse-plane moment across gait phases.

Results

We found that leftward linear momentum was generated most during right single support in straight-line gait and leftward turns. However, in contrast to straight-line gait, during leftward turns, average leftward force was applied across gait phases, with left single support generating significantly less leftward average force than other gait phases. Leftward angular momentum generation and average moment were greatest during left double support in both tasks. We observed some within-participant results that diverged from the group statistical findings, illustrating that although they are common, these momenta control strategies are not necessary.

Conclusions

Older adults generated transverse-plane linear and angular momentum during consistent phases of gait during straight-line gait and 90° turns, potentially indicating a shared control strategy. Understanding momentum control within each phase of gait can help design more specific targets in gait and balance training interventions.

Introduction

Linear and angular momentum must be generated and regulated (i.e., controlled) in the transverse plane to walk in a straight-line and to navigate real-world environments that require turning while walking. To walk in daily life, these momenta must be controlled through multilayered sub-system controller actions (e.g., muscle torques, etc.) so that the destination is reached without a fall [1]. Notably, up to 50% of our daily steps are part of turning gait, depending on the environment [2], and turning challenges momenta control beyond the demands of straight-line gait [3]. In older adults, turns are more difficult to execute due to age-related physiological changes which affect momenta control, even in healthy older adults, such as declines in muscle strength and coordination [4].

Prior research has described linear and angular momentum patterns during straight-line gait in healthy young and older adults towards quantifying balance. In straight-line gait, linear momentum exhibits small oscillations about zero in the medial–lateral (ML) direction [5] as weight shifts from one footfall to the next. Other work has shown that angular momentum during straight-line gait is maintained near zero, oscillating about zero in each plane over the course of the gait cycle [1]. Coordinating linear and angular momenta in straight-line gait allows maintenance of a constant speed and direction while facilitating balance. In turns, less is known about the neuromechanics of momenta control.

In walking turns, transverse-plane linear and angular momentum must be redirected towards the new direction of travel [6]. Specifically, linear momentum must be generated in the new desired direction travel so that the center of mass (COM) trajectory can redirect. In the angular domain, angular momentum must be generated to rotate the body about a vertical axis passing through the COM to change the body’s facing direction. While there are few prior studies about how older adults’ momentum is controlled during turns, in young and middle aged healthy adults, transverse-plane linear momentum redirection has been shown to occur via medially directed forces over the course of the “outside” foot’s stance phase (e.g., right leg stance phase during leftward turn) [7,8,9]. During turns, transverse-plane angular momentum diverges from oscillating about zero [3] in order to achieve body rotation about vertical. For example, during a 90° turn, average transverse-plane angular momentum was greater than it was during straight-line gait [10].

Investigating momentum generation within each of the four phases of gait is helpful because each gait phase affords unique mechanical contexts and turning while walking can occur over multiple steps [2]. This detailed information can be used in future rehabilitative practices to help diagnose motor control disfunction and train momenta generation strategies specific to base of support contexts. For example, if axial body rotation and balance are facilitated when both legs are in contact with the ground, gait retraining approaches can provide more specific body rotation targets for double support gait phases. Using a framework to investigate the contribution of each gait phase to momenta control, in young adults we found indicators of momenta control strategies that were specific to each gait phase during seemingly disparate tasks [6]. Specifically, during straight-line gait, pre-planned and late-cued 90° leftward turns, leftward transverse-plane linear and angular momentum were primarily generated during right single support and left double support phases, respectively The mechanical context to generate linear and angular impulses differs greatly as the COM and base of support relationship changes between single and double support phases in bipedal locomotion. Thus, our previous findings in young adults suggest that they leverage transverse-plane linear and angular momenta control specific to the gait phases during both straight-line gait and walking turns, despite differences in momenta control demands and footfall patterns across these tasks [6].

The primary purpose of this study was to understand whether transverse-plane linear and angular momentum generation in older adults occurs during the same phases of gait in straight-line gait and 90° turns. We hypothesized that both the straight-line gait and 90° left turn tasks will exhibit (1) the largest increase in linear momentum (Δp_x) and average leftward force (F_x,avg) towards the new direction of travel during right single support vs. other gait phases, and (2) the largest leftward change in transverse-plane angular momentum (ΔH_z) and average moment (M_z,avg) during left double support vs. other gait phases.

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