Simultaneous bidirectional hindlimb locomotion in decerebrate cats

We show that epidural spinal cord stimulation can elicit stable bidirectional locomotion of decerebrate cats on a split-belt treadmill. The stepping pattern of one limb was similar to unidirectional forward walking and, the other—was similar to unidirectional backward walking. This confirms that spinal and brainstem circuitry are sufficient to control such complex and extraordinary motor tasks driven by somatosensory input. Interlimb coordination during forward and backward walking was preserved in 2 out of 4 animals during ‘extreme’ conditions when one of the treadmill belts was stopped. Bidirectional locomotion worsened but was still possible after temporary spinalization by cooling the spinal cord on a low thoracic level. These present evidence for the great degree of the automatism for this stepping mode defined by the spinal neuronal networks.

Lower extremity coordination during walking in persons who are blind and sighted controls: A preliminary report

Walking is the most common mode of physical activity for individuals who are blind. However, this population tends to be physically inactive, possibly due to alterations in coordination patterns during walking. Therefore, the purpose of this study was to examine lower extremity coordination patterns during walking in persons who are blind, and age-, sex-, and body mass index–matched sighted controls. Five persons who are blind performed level walking independently (with a cane) and with a human guide. Sighted controls walked at matched speeds for both conditions. A 10-camera motion capture system was used to record segmental kinematics during both walking conditions. Angle–angle plots and modified vector coding was used to present inter-limb (left/right thigh) and intra-limb (ankle–hip, ankle–knee, and knee–hip) couplings across both walking conditions for each group. Frequency of coupling patterns was compared between groups using Mann–Whitney’s U tests. Inter- and intra-limb coordination patterns were similar between both groups during independent and guided walking conditions (all p > .05). Angle–angle plots depict reduced segmental and joint motion in persons who are blind compared with sighted controls. Although the visual feedback system is integral for coordination during complex tasks, persons who are blind perform level walking with similar lower extremity coordination patterns to sighted controls. Reductions in spatiotemporal and range of motion are likely linked to a more hesitant stepping pattern due to unfamiliarity with the environment.

Stepping pattern changes in the caterpillar Manduca sexta: the effects of orientation and substrate

ABSTRACTMost animals can successfully travel across cluttered, uneven environments and cope with enormous changes in surface friction, deformability and stability. However, the mechanisms used to achieve such remarkable adaptability and robustness are not fully understood. Even more limited is the understanding of how soft, deformable animals such as tobacco hornworm Manduca sexta (caterpillars) can control their movements as they navigate surfaces that have varying stiffness and are oriented at different angles. To fill this gap, we analyzed the stepping patterns of caterpillars crawling on two different types of substrate (stiff and soft) and in three different orientations (horizontal and upward/downward vertical). Our results show that caterpillars adopt different stepping patterns (i.e. different sequences of transition between the swing and stance phases of prolegs in different body segments) based on substrate stiffness and orientation. These changes in stepping pattern occur more frequently in the upward vertical orientation. The results of this study suggest that caterpillars can detect differences in the material properties of the substrate on which they crawl and adjust their behavior to match those properties.

Biomechanical analysis of curb ascent in persons with Ertl and non-Ertl transtibial amputations

Background: Persons with transtibial amputation report curb negotiation is more challenging than negotiating stairs. It is unknown if amputation technique influences curb negotiation ability. Traditional transtibial amputation surgical techniques do not join the distal tibia and fibula (non-Ertl), whereas a transtibial osteomyoplastic amputation (Ertl) creates a “bone bridge” connection. The Ertl may facilitate ambulation through greater residual end load bearing. Objectives: To determine if ability to negotiate a curb differs between Ertl and non-Ertl groups. Study design: Cross-sectional study. Methods: Non-Ertl ( n = 7) and Ertl ( n = 5) participants ascended a 16-cm curb using their amputated and intact limb as the lead limb. Motion data and ground reaction forces were used to calculate ankle, knee, hip, and total limb work for ground and curb steps. Results: On the ground, the amputated limb of both groups produced less work than the intact limb. In contrast, on the curb step, the Ertl amputated limb generated more net hip work than the non-Ertl amputated limb. As a result, the net limb work of the Ertl amputated limb did not differ from the non-amputated limbs. Conclusion: Comparisons between the amputated limb of Ertl and non-Ertl groups suggest use of a different curb stepping pattern between groups. Clinical relevance These findings suggest that surgical technique may influence curb negotiation ability in individuals with transtibial amputation. Specifically, the Ertl group is able to produce more hip power than the non-Ertl group while negotiation a curb which may be attributed to the increased ability to end-load bear on the residual limb.

Walking kinematics in the polymorphic seed harvester ant Messor barbarus: influence of body size and load carriage

Ants are famous in the animal kingdom for their amazing load carriage performances. Yet, the mechanisms that allow these insects to maintain their stability when carrying heavy loads have been poorly investigated. Here we present a study of the kinematics of loaded locomotion in the polymorphic seed-harvesting ant Messor barbarus. In this species big ants have larger heads relative to their size than small ants. Hence, their center of mass is shifted forward, and the more so when they are carrying a load in their mandibles. We tested the hypothesis that this could lead to big ants being less statically stable than small ants, thus explaining their lower load carriage performances. When walking unloaded we found that big ants were indeed less statically stable than small ants but that they were nonetheless able to adjust their stepping pattern to partly compensate for this instability. When ants were walking loaded on the other hand, there was no evidence of different locomotor behaviors in individuals of different sizes. Loaded ants, whatever their size, move too slowly to maintain their balance through dynamic stability. Rather, they seem to do so by clinging to the ground with their hind legs during part of a stride. We show through a straightforward model that allometric relationships have a minor role in explaining the differences in load carriage performances between big ants and small ants and that a simple scale effect is sufficient to explain these differences.

Accelerating locomotor savings in learning: compressing four training days to one

Acquiring new movements requires the capacity of the nervous system to remember previously experienced motor patterns. The phenomenon of faster relearning after initial learning is termed “savings.” Here we studied how savings of a novel walking pattern develops over several days of practice and how this process can be accelerated. We introduced participants to a split-belt treadmill adaptation paradigm for 30 min for 5 consecutive days. By training day 5, participants were able to produce near-perfect performance when switching between split and tied-belt environments. We found that this was due to their ability to shift specific elements of their stepping pattern to account for the split treadmill speeds from day to day. We also applied a state-space model to further characterize multiday locomotor savings. We then explored methods of achieving comparable savings with less total training time. We studied people training only on day 1, with either one extended split-belt exposure or alternating four times between split-belt and tied-belt conditions rapidly in succession. Both of these single-day training groups were tested again on day 5. Experiencing four abbreviated exposures on day 1 improved the performance on day 5 compared with one extended exposure on day 1. Moreover, this abbreviated group performed similarly to the group that trained for 4 consecutive days before testing on day 5, despite only having one-quarter of the total training time. These results demonstrate that we can leverage training structure to achieve a high degree of performance while minimizing training sessions. NEW & NOTEWORTHY Learning a new movement requires repetition. Here, we demonstrate how to more efficiently train an adapted walking pattern. By compressing split-belt treadmill training delivered over 4 days to four abbreviated bouts of training delivered on the first day of training, we were able to induce equivalent savings over a 5-day span. These results suggest that we can manipulate the delivery of training to most efficiently drive multiday learning of a novel walking pattern.

Source to sink sandstone-mudstone proportion and facies distribution across a third-order clastic wedge, Cretaceous Western Interior Seaway

The Iles Clastic Wedge is a 500 m thick, 3 My duration, third-order sequence that built out eastward in the Cretaceous Western Interior Seaway. The wedge also contains high-frequency regressive-to-transgressive sequences that are irregularly stacked in a basinward-stepping pattern (lower limb) and in a landward-stepping pattern (upper limb). The entire wedge and the component cycles were analyzed in terms of vertically monitored sandstone-mudstone proportion, thickness, and facies distribution. The measured profiles through the Iles Clastic Wedge form a 300 km long, source-to-sink transect from southeast Rock Springs uplift, Wyoming to Kremmling, Colorado. The sandstone proportion in the entire wedge (and also in the basinward-stepping half of the wedge) attains a maximum in the proximal reaches (fluvial and tidal-fluvial/estuarine channels) of the study transect and decreases unsteadily toward the medial and distal zone. A slight secondary increase in sand proportion also appears irregularly in the medial shoreline zone. On the other hand, the sandstone proportion in the landward-stepping half of the wedge reaches a maximum in the medial (tidal-fluvial and estuarine channels and delta-front) to distal zone (basinal regressive delta) of the wedge and decreases slightly sourceward. Along individual fourth-order sequences, the sandstones and mudstones indicate a more nuanced partitioning, with three marked sandstone maxima (proximal, medial, and distal zones), separated by zones with abundant mudstone. These sandstone peaks are produced by the presence of fluvial and tidal-fluvial/estuarine channel sandstones in the most proximal zone, delta front/shoreface in the medial reaches, and basinal regressive delta front in the distal zone. The mudstone peaks represent the muddy, coal-bearing coastal plain and the prodelta area. This accentuated sandstone and mudstone partitioning at shorter time scales (few 100 Ky) becomes blurred at the longer time scale (3 My) because of the progressive basinward, then landward, offset of successive high-frequency sequences that form the larger clastic wedge.

Split-arm swinging: the effect of arm swinging manipulation on interlimb coordination during walking

Control mechanisms for four-limb coordination in human locomotion are not fully known. To study the influence of arm swinging (AS) on bilateral coordination of the lower limbs during walking, we introduced a split-AS paradigm in young, healthy adults. AS manipulations caused deterioration in the anti-phased stepping pattern and impacted the AS amplitudes for the contralateral arm, suggesting that lower limb coordination is markedly influenced by the rhythmic AS during walking.

Angular measurements of the dynein ring reveal a stepping mechanism dependent on a flexible stalk

The force-generating mechanism of dynein differs from the force-generating mechanisms of other cytoskeletal motors. To examine the structural dynamics of dynein’s stepping mechanism in real time, we used polarized total internal reflection fluorescence microscopy with nanometer accuracy localization to track the orientation and position of single motors. By measuring the polarized emission of individual quantum nanorods coupled to the dynein ring, we determined the angular position of the ring and found that it rotates relative to the microtubule (MT) while walking. Surprisingly, the observed rotations were small, averaging only 8.3°, and were only weakly correlated with steps. Measurements at two independent labeling positions on opposite sides of the ring showed similar small rotations. Our results are inconsistent with a classic power-stroke mechanism, and instead support a flexible stalk model in which interhead strain rotates the rings through bending and hinging of the stalk. Mechanical compliances of the stalk and hinge determined based on a 3.3-μs molecular dynamics simulation account for the degree of ring rotation observed experimentally. Together, these observations demonstrate that the stepping mechanism of dynein is fundamentally different from the stepping mechanisms of other well-studied MT motors, because it is characterized by constant small-scale fluctuations of a large but flexible structure fully consistent with the variable stepping pattern observed as dynein moves along the MT.