Minimum toe clearance adaptations to floor surface irregularity and gait speed

Abstract

Toe speed during gait generally nears its maximum while its height reaches a local minima approximately halfway through swing phase. Trips are thought to frequently occur at these local minima (minimum toe clearance or MTC events) and trip risk has been quantified using the minimum distance between the toe and ground here (MTC). This study investigated MTC on floor surfaces with and without multiple small obstacles. After shoes and floor surfaces were digitized, 14 unimpaired subjects (half women) each traversed a 4.88 m walkway 4 times at slow, preferred, and fast speeds across surfaces with no obstacles, visible obstacles, and hidden obstacles. Both surfaces with obstacles had the same random obstacle configuration. Shoe and body segment motions were tracked using passive markers and MTC and joint kinematics calculated. All MTC and kinematic variables tested significantly increased with faster instructed gait speed except the likelihood of MTC event occurrence (local minima in minimum toe clearance trajectory when foot is in upper quartile of speed). MTC events were less frequent for swing phases on surfaces with obstacles (80% vs. 98% for no obstacles). MTC values, when present, were doubled by the presence of visible obstacles (22.2 ± 7.3mm vs. 11.1 ± 5.7 mm) and further increased to 26.8 ± 7.1mm when these obstacles were hidden from view (all comparisons p ≤ 0.0003). These substantial floor surface-related changes in MTC event occurrences and values resulted from alterations in toe- and heel-clearance trajectories caused by subtle but significant changes in joint kinematics that did not exceed 10% each joint's swing phase range of motion.

Figure 1

Representative experimental shoe (a) and shoe mounted on custom jig being digitized (b).

Figure 2

Representative data of digitized shoe sole and embedded markers.

Figure 3

Custom rolling digitizing wand based on CalTester.

Figure 4

Unequal-axis plot of piecewise 3rd-order polynomial fit for floor surface segments without obstacles (a) and equal-axis plot of floor surface segments with obstacles (b). Note that the shape and alignment of these polynomial surfaces reflects the unevenness, inconsistencies, and slopes of flooring surface sections affixed to the laboratory floor.

Figure 5

Bar plots of percentage of valid gait cycles with an MTC event for each subject. Data are plotted by instructed gait speed (slow = left column row, preferred = middle column, fast = right column) and by flooring surface condition (no obstacles = top row, visible obstacles = middle row, hidden obstacles = bottom row).

Figure 6

Ensemble means (±1SD envelope) of minimum distances from toe to floor surface across the swing phase of gait plotted by instructed gait speed (slow = left, preferred = middle, fast = right) and flooring surface condition.

Figure 7

Ensemble means (±1SD envelope) of hip flexion (top row), knee flexion (middle row), and ankle dorsiflexion (bottom row) angles across the swing phase of gait plotted by instructed gait speed (slow = left, preferred = middle, fast = right) and flooring surface condition.

Figure 8

Traces of minimum distances from toe (blue) and heel (green) shoe segments to floor surface across the swing phase of gait on surfaces with no obstacles (left), visible obstacles (center), and hidden obstacles (right) for all viable gait cycles of the left foot of a single subject walking at preferred speed. Note that at the local minimum in minimum heel clearance just prior to ground contact, the swing foot is no longer moving near its maximum speed and the walker’s center of mass is no longer in front of the base of support if the swing foot motion is arrested. Thus, if the heel contacts the ground at this point it merely “skips” or skids on the ground without substantially interrupting the gait pattern. This subject (Female #3) exhibited the strongest reduction in MTC event frequency on more challenging surfaces and is the best example of these adaptations to more challenging surface conditions. Solid lines indicate the trace that is closest to the floor surface (including obstacles if present) during the upper quartile of toe centroid speed. Minimum toe clearance (MTC) events circled in red. Y-axis range limited to better display region of interest; peaks in truncated minimum heel clearance traces reach approximately 160mm around 0.1s into swing phase.