Step time asymmetry but not step length asymmetry is adapted to optimize energy cost of split‐belt treadmill walking

Abstract

Key points The relationship between spatiotemporal gait asymmetry and walking energetics is currently under debate. The split‐belt treadmill paradigm has been used to study adaptation of spatiotemporal gait parameters in relation to energetics, but it remains unclear why people reduce asymmetry in step lengths, but prefer asymmetry in step times. In this study we characterized the effects of step time asymmetry and step length asymmetry on energy cost during steady‐state walking on a split‐belt treadmill at increasing speed‐differences. Both the optimal and preferred step time asymmetry increased with greater speed differences, while preferred step lengths remained constant and nearly symmetric. Preferred asymmetric step times were energetically optimal across all speed‐difference conditions, while preferred step length asymmetry was not optimal. The findings show that humans will adopt an asymmetric gait that is associated with an energy reduction and suggest that step time asymmetry plays a dominant role in shaping the energetic cost of gait asymmetry. Abstract Healthy human walking is symmetric and economical; hemiparetic and amputee gait is often asymmetric and requires more energy. Consequently, asymmetry has been attributed to account for the added energy cost of pathological gait. But it is also possible that asymmetric gait may be adopted if it is energetically optimal under certain biomechanical and neurological constraints of the locomotor system. Here, we assessed how preferred asymmetry in step times and step lengths of healthy human gait is adapted during split‐belt treadmill walking and tested the hypothesis that asymmetry is adapted to optimize metabolic energy cost. Ten healthy, young participants walked on a split‐belt treadmill in three conditions in which the average belt speed was always 1.25 m s–1 and the speed difference between the belts was 0.5 m s–1, 1.0 m s–1 and 1.5 m s–1 while a range of values of step time asymmetry and step length asymmetry were enforced. We found that preferred step time asymmetry increased with greater speed differences while preferred step length asymmetry remained constant and nearly symmetric. With increasing speed differences participants increased their preferred value of step time asymmetry to coincide with the lowest energy cost. However, our results show that preferred step length asymmetry was not optimal even with extensive experience of split‐belt treadmill walking. Overall, our results indicate that humans will adopt an asymmetric gait that is associated with an energy reduction and suggest that step time asymmetry plays a dominant role in shaping the energetic cost of gait asymmetry.

Contributions of spatial and temporal control of step length symmetry in the transfer of locomotor adaptation from a motorized to a non-motorized split-belt treadmill

“…In either case, the temporal component was free to express the adapted asymmetry, independent of the spatial component, during the transfer condition. These results are consistent with previous findings that spatial and temporal control of walking gait are dissociable [4][5][6]8,20]. A recent study demonstrated that manipulation of spatial control during split-belt adaptation had no effect on temporal after-effects, but manipulation of temporal adaptation influenced the spatial aftereffects [8].…”

Exploration-based learning of a stabilizing controller predicts locomotor adaptation

“…Also, Figure 6 shows how the energy cost landscape has greater curvature along step time asymmetry rather than the step length asymmetry, again implying faster convergence for the energy optimizing gradient descent in the step time direction than in the step length direction. One recent study 38 with a shorter adaptation timescale observed that in that short timescale, split belt walking converged to the energy optimal step time but not the energy optimal step length. This may simply be because, as our model suggests, step time asymmetry may converge faster than step length asymmetry due to the aforementioned reasons.…”

Exergaming as a Functional Test Battery in Patients Who Received Arthroscopic Ankle Arthrodesis: Cross-sectional Pilot Study

“…This can be explained by the angle between the longitudinal axis of the foot and the walking direction; negative values indicate an inward rotation and positive values indicate an outward rotation. Healthy human walking is symmetrical and economical; however, the walking of people who received AA is often asymmetrical and requires more energy [ 18 ].…”