Locomotor patterns change over time when exposed to an uneven surface

Abstract

During walking, uneven surfaces impose new demands for controlling balance and forward progression at each step. It is unknown to what extent walking may be refined given an amount of stride-to-stride unpredictability at the distal level. Here, we explored the effects of an uneven terrain surface on whole-body locomotor dynamics immediately following exposure and after a familiarization period. Eleven young, unimpaired adults walked for 12 min on flat and uneven terrain treadmills. The whole-body center of mass excursion range (COM exc) and peak velocity (COM vel), step length and width were estimated. On first exposure to uneven terrain, we saw significant increases in medial-lateral COM exc and lateral COM vel , and in the variability of COM exc , COM vel and foot placement in both anterior-posterior and medial-lateral directions. Increases in step width and decreases in step length supported the immediate adoption of a cautious, restrictive solution on uneven terrain. After familiarization, step length increased and the variability of anteriorposterior COM vel and step length reduced, while step width and lateral COM vel reduced, alluding to a refinement of movement and a reduction of conservative strategies over time. However, the variability of medial-lateral COM exc and lateral COM vel increased, consistent with the release of previously constrained degrees of freedom. Despite this increase in variability, a strong relationship between step width and medial-lateral center of mass movement was maintained. Our results indicate that movement strategies of unimpaired adults when walking on uneven terrain can evolve over time with longer exposure to the surface.

Changes in human walking dynamics induced by uneven terrain are reduced with ongoing exposure, but a higher variability persists

“…Such a strategy could reduce the likelihood of a crossover step, or of an abrupt misalignment of the body with the plane of progression that might prompt a fall over the lateral border of the foot. Alternatively, this observation may be related to a concomitant reduction in step length 24 , proposed to be a conservative mechanism to aid dynamic balance, which affects momenta due to a change in the effect of the ground reaction force 12 . Should this be the case, it remains unclear whether L R is reduced as a consequence of a change in step length or actively controlled to reduce it.…”

“…The latter device, illustrated in Fig. 2 has been previously shown to successfully invoke different midstance postures at each step, thus perpetually changing the direction of action of the ground reaction force during walking 24 . The surface, with a maximum depth of approximately 2.2 cm is sufficiently shallow to permit heel-toe gait, and the pattern is reflected about the center of the belt and offset to provide both feet with equal probability of encountering the same contours.…”

Uneven terrain treadmill walking in younger and older adults

“…Thus, participants had 11% more space to move anteroposteriorly and 25% more space to move mediolaterally in the present study. Additionally, the treadmill in [20] had rails to the left and right of the participants which could further limit the range of mediolateral movement, whereas we purposefully removed them.…”

“…This contrasts with dual-task paradigms, which distract participants cognitively, and with discrete physical perturbations, which challenge participants intermittently. Some studies have used modified treadmills to create uneven surfaces [19][20][21][22][23]. However, previous studies examined only one uneven surface and compared it with normal treadmill walking rather than parametrically varying the terrain.…”

Modular footwear that partially offsets downhill or uphill grades minimizes the metabolic cost of human walking

“…Participants then performed a 10 min warm-up [34] to become habituated with the shoe construction and treadmill before data collection. The treadmill speed was set at 1 m s −1 [35,36]. All testing conditions lasted 5 minutes and were completed in a single session to avoid day-to-day variability and marker repositioning errors that would affect metabolic rate and biomechanical measurements.…”