More Like this

1. Multi-modal aquatic hexapods use hybrid walking-swimming gaits in shallow water

   https://doi.org/10.1093/icb/icag060  

   Tikader, Snigdha S; Handwork, Alex M; Byron, Margaret L (June 2026, Integrative And Comparative Biology)

   Abstract Many animals use adaptive locomotor strategies to traverse the physical boundaries between aquatic, aerial, and terrestrial environments; these strategies can provide insight into not only evolutionary relationships but novel bio-inspired designs. Insects capable of locomotion both underwater and on land can offer a compelling window into the underlying mechanics of amphibious locomotion. This study focuses on understanding how aquatic hexapods (Dytiscidae and Notonectidae) transition their locomotion from dry land to shallow water. Using high speed videography and kinematic tracking, we quantify different gaits at varying water depth (below, at, and above body height) as insects walk in a straight line. On dry land, diving beetles use the alternating tripod gait common to most terrestrial hexapods, while backswimmers primarily use their anterior legs to crawl at slower speeds. However, in shallow water, both insects exhibit novel “hybrid” gaits characterized by synchronous power/recovery strokes in the metathoracic legs (as in swimming) while the anterior legs maintain contact with the substrate (as in walking). At water levels at or above body height, both insects shift to full swimming, where there is no contact with the substrate and the body is propelled primarily or entirely by the bristled metathoracic legs. Our findings uncover how locomotion strategies can be adapted in response to competing forces (water resistance/fluid drag, buoyancy, and ground reaction) and demonstrate that limb coordination strategies can be tuned to transitional environments and across interfaces. These results provide insight into a previously understudied aspect of insect locomotion, and can fuel design inspiration for amphibious devices operating effectively across aquatic and terrestrial domains. 

   more » « less
2. Analysis of Continuously Varying Kinematics for Prosthetic Leg Control Applications

   https://doi.org/10.1109/TNSRE.2020.3045003  

   Embry, Kyle R.; Gregg, Robert D. (December 2020, IEEE Transactions on Neural Systems and Rehabilitation Engineering)

   null (Ed.)

   Powered prosthetic legs can improve the quality of life for people with transfemoral amputations by providing net positive work at the knee and ankle, reducing the effort required from the wearer, and making more tasks possible. However, the controllers for these devices use finite state machines that limit their use to a small set of pre-defined tasks that require many hours of tuning for each user. In previous work, we demonstrated that a continuous parameterization of joint kinematics over walking speeds and inclines provides more accurate predictions of reference kinematics for control than a finite state machine. However, our previous work did not account for measurement errors in gait phase, walking speed, and ground incline, nor subject-specific differences in reference kinematics, which occur in practice. In this work, we conduct a pilot experiment to characterize the accuracy of speed and incline measurements using sensors onboard our prototype prosthetic leg and simulate phase measurements on ten able-bodied subjects using archived motion capture data. Our analysis shows that given demonstrated accuracy for speed, incline, and phase estimation, a continuous parameterization provides statistically significantly better predictions of knee and ankle kinematics than a comparable finite state machine, but both methods' primary source of predictive error is subject deviation from average kinematics. 

   more » « less
3. Augmenting Human-Inspired Phase Variables Using a Canonical Dynamical System

   https://doi.org/10.1109/ROBIO64047.2024.10907279  

   Driscoll, Timothy; Walker, Ian; Lv, Ge (December 2024, IEEE)

   Accurately parameterizing human gait cycles is crucial for developing control systems for lower-limb wearable robots. Previous studies on characterizing human gait cycle investigated the use of human-inspired phase variables, but they lack robustness and adaptability to accommodate for transitions that occur between locomotor tasks. This paper proposes augmenting the traditional phase variables with a canonical dynamical system. This system considers the differences between the estimated and true thigh angular velocities, based on which the Fourier series coefficients and phase information will be dynamically updated via an adaptive frequency oscillator. Experiments with six able-bodied participants on level ground, inclines, and declines walking show that the augmented phase variable adapts to various locomotor tasks and transitions better than the traditional approach. 

   more » « less
4. Program of the 88th Annual Meeting of the American Association of Physical Anthropologists

   https://doi.org/10.1002/ajpa.23802  

   Dunham, Noah T.; McNamara, Allison; Demes, Brigitte; Johnson, Laura A.; Shapiro, Liza J.; Young, Jesse W. (February 2019, American Journal of Physical Anthropology)

   Laboratory investigations have provided important insight into the functional underpinnings of primate locomotor performance; however, it is unclear to what extent gait patterns in the laboratory reflect those of primates moving in natural settings. We filmed quadrupedal loco-motor activity in eight platyrrhine species at the Tiputini Biodiversity Station, Ecuador, and three additional platyrrhine species at La Suerte Biological Field Station, Costa Rica, and also quantified the diameter and orientation of locomotor substrates using remote sensors (N = 1,233 strides). We compared overall arboreal quadrupedal gait kinematic patterns in free-ranging individuals to those of laboratory platyrrhine congenerics. As expected, gait kinematics of free-ranging individuals were more variable than laboratory counterparts. Within the free-ranging dataset, Ateles and Alouatta increased limb phase on inclines (p=0.04; p=0.002, respectively), Lagothrix increased duty factors on inclines (p=0.002), Cebus increased duty factors on declines (p=0.02), and both Saimiri and Saguinus displayed an inverse relationship between limb phase and substrate diameter (p=0.05; p=0.03, respectively). This study confirms the preference for diagonal sequence gaits in free-ranging primates (i.e., 87.9% of all recorded symmetrical strides) and that in both settings primates tend to adjust gait patterns to promote security through longer contact times on non-horizontal substrates and increased limb phase on inclined substrates. We show that laboratory and field investigations of primate locomotion yield consistent patterns but that field studies can capture additional aspects of gait variability and flexibility in response to the increased substrate complexity of natural environments. 

   more » « less
5. Treadmill vs. overground walking: different response to physical interaction

   https://doi.org/10.1152/jn.00176.2017  

   Ochoa, Julieth; Sternad, Dagmar; Hogan, Neville (October 2017, Journal of Neurophysiology)

   Rehabilitation of human motor function is an issue of growing significance, and human-interactive robots offer promising potential to meet the need. For the lower extremity, however, robot-aided therapy has proven challenging. To inform effective approaches to robotic gait therapy, it is important to better understand unimpaired locomotor control: its sensitivity to different mechanical contexts and its response to perturbations. The present study evaluated the behavior of 14 healthy subjects who walked on a motorized treadmill and overground while wearing an exoskeletal ankle robot. Their response to a periodic series of ankle plantar flexion torque pulses, delivered at periods different from, but sufficiently close to, their preferred stride cadence, was assessed to determine whether gait entrainment occurred, how it differed across conditions, and if the adapted motor behavior persisted after perturbation. Certain aspects of locomotor control were exquisitely sensitive to walking context, while others were not. Gaits entrained more often and more rapidly during overground walking, yet, in all cases, entrained gaits synchronized the torque pulses with ankle push-off, where they provided assistance with propulsion. Furthermore, subjects entrained to perturbation periods that required an adaption toward slower cadence, even though the pulses acted to accelerate gait, indicating a neural adaptation of locomotor control. Lastly, during 15 post-perturbation strides, the entrained gait period was observed to persist more frequently during overground walking. This persistence was correlated with the number of strides walked at the entrained gait period (i.e., longer exposure), which also indicated a neural adaptation. NEW & NOTEWORTHY We show that the response of human locomotion to physical interaction differs between treadmill and overground walking. Subjects entrained to a periodic series of ankle plantar flexion torque pulses that shifted their gait cadence, synchronizing ankle push-off with the pulses (so that they assisted propulsion) even when gait cadence slowed. Entrainment was faster overground and, on removal of torque pulses, the entrained gait period persisted more prominently overground, indicating a neural adaptation of locomotor control. 

   more » « less