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In control of walking, sensory signals of decreasing forces are used to regulate leg lifting in initiation of swing and to detect loss of substrate grip (leg slipping). We used extracellular recordings in two insect species to characterize and model responses to force decrements of tibial campaniform sensilla, receptors that detect forces as cuticular strains. Discharges to decreasing forces did not occur upon direct stimulation of the sites of mechanotransduction (cuticular caps) but were readily elicited by bending forces applied to the leg. Responses to bending force decreases were phasic but had rate sensitivities similar to discharges elicited by force increases in the opposite direction. Application of stimuli of equivalent amplitude at different offset levels showed that discharges were strongly dependent upon the tonic level of loading: firing was maximal to complete unloading of the leg but substantially decreased or eliminated by sustained loads. The contribution of cuticle properties to sensory responses was also evaluated: discharges to force increases showed decreased adaptation when mechanical stress relaxation was minimized; firing to force decreases could be related to viscoelastic “creep” in the cuticle. Discharges to force decrements apparently occur due to cuticle viscoelasticity that generates transient strains similar to bending in the opposite direction. Tuning of sensory responses through cuticular and membrane properties effectively distinguishes loss of substrate grip/complete unloading from force variations due to gait in walking. We have successfully reproduced these properties in a mathematical model of the receptors. Sensors with similar tuning could fulfil these functions in legs of walking machines. NEW & NOTEWORTHY Decreases in loading of legs are important in the regulation of posture and walking in both vertebrates and invertebrates. Recordings of activities of tibial campaniform sensilla, which encode forces in insects, showed that their responses are specifically tuned to detect force decreases at the end of the stance phase of walking or when a leg slips. These results have been reproduced in a mathematical model of the receptors and also have potential applications in robotics.
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This content will become publicly available on September 1, 2026
Numerical simulation of flow around the legs during walking in water with implications for hydrotherapeutic exercise
One of the common hydrotherapeutic exercises is walking in water because buoyancy reduces joint loading and increases mobility for a patient. The fluid drag forces (the forces that act on the person from the fluid in the direction opposing the direction of motion) cause changes in muscle activations, as walking in water changes the forces that act on the leg compared with overground walking. Here, through a series of numerical simulations, we quantify how the flow forces that act on the leg due to its motion in water change over a walking gait cycle. We show that besides drag forces that act on the walking legs and peak when the leg is accelerated forward, relatively large lateral forces (in the direction perpendicular to the direction of motion) also act on the leg. These forces are caused by the rapid acceleration of the opposite leg when the two legs are close, creating an asymmetric pressure distribution around the leg. These results are unexpected and could have significant implications for designing hydrotherapeutic plans for patients by considering the lateral forces besides the drag forces that act on the body while walking in water.
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- Award ID(s):
- 2024409
- PAR ID:
- 10629221
- Publisher / Repository:
- ScienceDirect
- Date Published:
- Journal Name:
- Journal of Fluids and Structures
- Volume:
- 137
- Issue:
- C
- ISSN:
- 0889-9746
- Page Range / eLocation ID:
- 104352
- Subject(s) / Keyword(s):
- Computational fluid dynamicsVorticesHydrotherapyWalking
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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