Trunk control during gait: Walking with wide and narrow step widths present distinct challenges
Introduction
Maintaining stability is one of the primary goals in human locomotion. In contrast with sagittal plane stability, which is largely achieved through passive mechanisms, frontal plane stability during gait requires active control (Bauby and Kuo, 2000, Kuo and Donelan, 2010). Frontal plane stability during walking is achieved through a combination of different strategies, including adjusting mediolateral motion of the body’s center of mass (CoM) (Arvin et al., 2016a), manipulating mediolateral foot placement (Bruijn and van Dieën, 2018), or external rotation of the foot (Rebula et al., 2017). The trunk accounts for 48% of the body mass and is the largest contributor to the CoM (MacKinnon and Winter, 1993, Prince et al., 1994). Therefore, how the trunk is controlled will directly influence the CoM, and in some cases adjustment of the CoM motion is preferred over modifying foot placement (Best et al., 2019). The trunk should not be considered a rigid body, since structurally it involves multiple linked segments and degrees of freedom that need to be fine-tuned. When these degrees of freedom within the trunk are constrained with an orthosis, an impact on CoM excursion and step width is observed (Arvin et al., 2016b).
Although the relationship between CoM and lateral foot placement has been extensively studied (Arvin et al., 2016a, Bruijn and van Dieën, 2018, Hurt et al., 2010, McAndrew Young and Dingwell, 2012, Perry and Srinivasan, 2017, Stimpson et al., 2018, Wang and Srinivasan, 2014), the within-trunk control in response to step width has not been well-investigated. Furthermore, the use of strings or tape to prescribe step width in previous studies required participants to look down, affecting their trunk motion (Arvin et al., 2016a, Perry and Srinivasan, 2017). We therefore designed a study using visual feedback at eye-level to investigate trunk control at different step widths. This study will provide insight into walking mechanics and a basis for understanding and training trunk motion in different populations, such as persons with spinal pathology, balance issues, or older adults.
During gait, the mass of the trunk is controlled in the frontal plane mainly by the spinal musculature and the hip abductors (MacKinnon and Winter, 1993). Studies have primarily focused on the contribution of hip abductors to modifying foot placement (Rankin et al., 2014) and stability during stance phase (Kubinski et al., 2015). However, the role of paraspinal muscle activation has not received much research attention. A study on typical walking demonstrated that paraspinal muscles at the lumbar region were the most highly activated among the C7 to L4 paraspinal muscles (Prince et al., 1994), but how the muscles’ activation patterns are modulated for different step widths is still unknown.
Walking with wider and narrower step widths places unique demands on the motor system. The preferred step width is likely to be selected to minimize energy cost without compromising stability (Donelan et al., 2001). Moving away from the preferred step width affects the inverted pendulum-like motion of the CoM and influences energy demands (Kuo et al., 2005). A previous study demonstrated that walking with wider step widths requires greater mechanical work to redirect the CoM, while walking with narrower step widths increases work associated with swinging the leg laterally to avoid the stance limb (Donelan et al., 2001). Walking with a narrower width also presents greater challenges to stability and increases demand on active postural control as the base of support decreases (Donelan et al., 2004, MacKinnon and Winter, 1993, Perry and Srinivasan, 2017). The current study will investigate whether trunk control varies continuously across step widths or presents as separate motor patterns in wide and narrow widths. If the latter is true, walking with wide and narrow widths can be viewed as two distinct tasks.
The purpose of this study was to characterize changes in trunk control during different prescribed step widths, and to compare the effects of wide and narrow step widths on trunk kinematics and muscle activation. We hypothesized that narrower widths will present greater stability demands and result in an increase in muscle co-activation, while wider widths will present greater mechanical demands and influence trunk kinematics.
Section snippets
Participants
Twenty healthy young adults participated in this study (14 females, 6 males; 26.25 ± 3.31 years; 165.54 ± 9.93 cm; 61.39 ± 12.71 kg; BMI = 22.21 ± 2.84 kg/m2). Participants were included if they were between 18 and 45 years old and excluded if they had a history of lower extremity or spine pathology or surgery. Participants gave written informed consent that was approved by the university’s institutional review board.
Instrumentation
Participants were instrumented with a lower extremity marker set and
Task performance
The average preferred step width (PSW) was 14.77 ± 2.92 cm, equivalent to 0.17 × leg length. Participants were able to match the different target step widths using the visual feedback. They made small but consistent positive errors that were dependent on step width, with the largest errors occurring at the narrowest step widths (Fig. 3A). There was a significant difference in constant step width error between step widths (F(4,76) = 18.93, p < 0.001) (Fig. 3B). Post-hoc test revealed a
Discussion
We investigated the effects of varying step width on trunk control and specifically compared the effects of wider and narrower step widths. We found that although CoM only varied along the mediolateral axis across step widths, trunk kinematics in all three planes were affected. The results indicated that walking with wide and narrow step widths may be viewed as two distinct tasks, where greater stability demands were present in narrow widths and greater mechanical demands were present in wider
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was supported by the International Society of Biomechanics Matching Dissertation Grant. The funding agency does not have any involvement in the design, execution, and the interpretation and write up of this study.
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2022, Journal of BiomechanicsCitation Excerpt :Previous investigations have also reported a smaller COM movement in healthy young and older adults when walking on narrow-step width (Arvin et al., 2016). This finding is not surprising because a change in the preferred step width affects the inverted pendulum-like motion of the COM (Shih et al., 2021). Narrow steps require tight control of the COM position in the frontal plane, reducing the moment applied by the ground reaction force and consequently decreasing the mediolateral body sway.