Foot placement in a body reference frame during walking and its relationship to hemiparetic walking performance

Abstract

Background: Foot placement during walking is closely linked to the body position, yet it is typically quantified relative to the other foot. The purpose of this study was to quantify foot placement patterns relative to body post-stroke and investigate its relationship to hemiparetic walking performance.

Methods: Thirty-nine participants with hemiparesis walked on a split-belt treadmill at their self-selected speeds and 20 healthy participants walked at matched slow speeds. Anterior-posterior and medial-lateral foot placements (foot center-of-mass) relative to body (pelvis center-of-mass) quantified stepping in body reference frame. Walking performance was quantified using step length asymmetry ratio, percent of paretic propulsion and paretic weight support.

Findings: Participants with hemiparesis placed their paretic foot further anterior than posterior during walking compared to controls walking at matched slow speeds (P<.05). Participants also placed their paretic foot further lateral relative to pelvis than non-paretic (P<.05). Anterior-posterior asymmetry correlated with step length asymmetry and percent paretic propulsion but some persons revealed differing asymmetry patterns in the translating reference frame. Lateral foot placement asymmetry correlated with paretic weight support (r=.596; P<.001), whereas step widths showed no relation to paretic weight support.

Interpretation: Post-stroke gait is asymmetric when quantifying foot placement in a body reference frame and this asymmetry related to the hemiparetic walking performance and explained motor control mechanisms beyond those explained by step lengths and step widths alone. We suggest that biomechanical analyses quantifying stepping performance in impaired populations should investigate foot placement in a body reference frame.

Figure 1. Calculation of Anterior-Posterior and Medial-Lateral foot placements relative to the pelvis

Abbreviations: IC – Initial-contact at 1st double-support (initial foot placement), FO – Foot-off at 2nd double-support (terminal foot position). This figure presents the foot placement variables calculated in a body reference frame. Body is referenced at the pelvis COM and foot is referenced at the foot COM. Variables were calculated as the AP and ML distance between foot COM and pelvis COM. Note, the arrows present the step length and step width calculated relative to other foot.

Figure 2. Foot Placement relative to pelvis during hemiparetic and healthy gait

Abbreviations: IC – Initial-contact at 1st double-support (initial foot placement), FO – Foot-off at 2nd double-support (terminal foot position), P- Paretic foot, N-Non-paretic foot, C-Control foot. The box plots indicate the range in the data. The central horizontal line is the median of the sample. The length of the box indicates the inter-quartile range with the upper and lower boundaries of the box indicating the upper and lower quartile, respectively. Circles represent sample values that statistically indicate outlier or extreme values (by SPSS software).

Figure 3. Relationship between anterior foot placement asymmetry relative to pelvis and step length asymmetry in participants with hemiparesis

This figure shows the relationship between asymmetry in foot placements relative to pelvis (body reference frame) and step length asymmetry (relative to the other foot). The vertical dashed lines indicate the step length symmetry ranges (45 ≤ PSR ≤ 55) and the horizontal dashed lines indicate symmetry ranges in the body reference frame (46 ≤ PSR ≤ 54) calculated similarly from healthy controls. Persons above the range take ‘Longer paretic’ steps than non-paretic and those below the range take ‘Shorter paretic’ steps than non-paretic. Note that, four persons (bold arrow) taking longer paretic than non-paretic step lengths placed their paretic and non-paretic feet symmetric with respect to the pelvis. On the other hand, three persons (dashed arrow) who were taking symmetric step lengths place their paretic foot closer to pelvis than non-paretic (i.e. shorter paretic steps in the body reference frame).

Figure 4. Relationship between step length asymmetry and anterior-posterior foot placement relative to pelvis in participants with hemiparesis

Abbreviations: IC – Initial-contact at 1st double-support (initial foot placement), FO – Foot-off at 2nd double-support (terminal foot position). This figure shows the relationship between step length asymmetry and between-phase asymmetry in foot placements relative to pelvis at IC and FO. The step length symmetry ranges (45 ≤ PSR ≤ 55) were calculated similarly from healthy controls. Note the posterior paretic foot position in persons taking ‘Longer paretic’ steps (PSR > 55). Some persons with severe step length asymmetry (PSR > 70%) never position their paretic foot posterior to the pelvis in this phase of their gait cycle (2nd double support). Similarly, severely asymmetric persons taking ‘Shorter paretic’ steps (PSR < 40%) place paretic foot much anterior to pelvis than posterior at foot-off. Also, compare the paretic posterior and non-paretic anterior placement relative to pelvis between the symmetric and asymmetric persons.

Figure 5. Relationship between paretic and non-paretic lateral foot placemen asymmetry relative to pelvis and percent weight supported on the paretic leg

This figure shows the relationship between lateral foot placement asymmetry and paretic leg weight supported. The greater lateral foot placement asymmetry (i.e., paretic foot placed wider relative to pelvis than non-paretic foot placement relative to pelvis) lesser the weight supported on the paretic leg during the stance phase.