Biology subjects

Rahmati, S. M.

Publications and source records attributed to Rahmati, S. M..

3 recordsLinked to original sources

bioRxiv2026

Posture and support geometry, rather than body size, dictate lateral dynamic stability in walking mammalian quadrupeds

Body size and limb posture vary widely across mammals and are expected to shape locomotor stability, yet direct comparative evidence remains limited. Here, we tested whether smaller, crouched mammals exhibit greater lateral dynamic stability than larger, more upright species by comparing treadmill walking in mice and cats at dynamically similar speeds. Using kinematic analyses and size normalized measures of stability, we show that mice are substantially more laterally stable than cats. This increased stability is associated with relatively wider step widths and more crouched limb posture, indicating that support geometry and posture play dominant roles in stabilizing locomotion. Despite these differences, both species regulate lateral balance on a step-by-step basis, as revealed by relationships between center of mass motion and subsequent adjustments of the border of support. Our findings demonstrate that locomotor stability does not scale simply with body size but depends critically on posture dependent strategies that differ across species. These results identify lateral stability as a key factor of locomotor adaptation and suggest that crouched postures in small mammals may reduce reliance on active neural control while enhancing robustness in complex environments. SUMMARY STATEMENTLateral dynamic stability during quadrupedal locomotion depends primarily on limb posture and support geometry rather than body size. Smaller mammals achieve greater stability through crouched postures and wider step widths, whereas larger mammals operate closer to stability limits and rely more heavily on active control.

neuroscience↗

bioRxiv2024

EFFECTS OF SPINAL TRANSECTION AND LOCOMOTOR SPEED ON MUSCLE SYNERGIES OF THE CAT HINDLIMB

It was suggested that during locomotion, the nervous system controls movement by activating groups of muscles, or muscle synergies. Analysis of muscle synergies can reveal the organization of spinal locomotor networks and how it depends on the state of the nervous system, such as before and after spinal cord injury, and on different locomotor conditions, including a change in speed. The goal of this study was to investigate the effects of spinal transection and locomotor speed on hindlimb muscle synergies and their time-dependent activity patterns in adult cats. EMG activities of 15 hindlimb muscles were recorded in 9 adult cats of either sex during tied-belt treadmill locomotion at speeds of 0.4, 0.7, and 1.0 m/s before and after recovery from a low thoracic spinal transection. We determined EMG burst groups using cluster analysis of EMG burst onset and offset times and muscle synergies using non-negative matrix factorization. We found five major EMG burst groups and five muscle synergies in each of six experimental conditions (2 states x 3 speeds). In each case, the synergies accounted for at least 90% of muscle EMG variance. Both spinal transection and locomotion speed modified subgroups of EMG burst groups and the composition and activation patterns of selected synergies. However, these changes did not modify the general organization of muscle synergies. Based on the obtained results, we propose an organization for a pattern formation network of a two-level central pattern generator that can be tested in neuromechanical simulations of spinal circuits controlling cat locomotion.

neuroscience↗

bioRxiv2024

ROLE OF FORELIMB MORPHOLOGY IN MUSCLE SENSORIMOTOR FUNCTIONS DURING LOCOMOTION IN THE CAT

Previous studies established strong links between morphological characteristics of mammalian hindlimb muscles and their sensorimotor functions during locomotion. Less is known about the role of forelimb morphology in motor outputs and generation of sensory signals. Here, we measured morphological characteristics of 46 forelimb muscles from 6 cats. These characteristics included muscle attachments, physiological cross-sectional area (PCSA), fascicle length, etc. We also recorded full-body mechanics and EMG activity of forelimb muscles during level overground and treadmill locomotion in 7 and 16 adult cats of either sex, respectively. We computed forelimb muscle forces along with force- and length-dependent sensory signals mapped onto corresponding cervical spinal segments. We found that patterns of computed muscle forces and afferent activities were strongly affected by the muscles moment arm, PCSA, and fascicle length. Morphology of the shoulder muscles suggests distinct roles of the forelimbs in lateral force production and movements. Patterns of length-dependent sensory activity of muscles with long fibers (brachioradialis, extensor carpi radialis) closely matched patterns of overall forelimb length, whereas the activity pattern of biceps brachii matched forelimb orientation. We conclude that cat forelimb muscle morphology contributes substantially to locomotor function, particularly to control lateral stability and turning, rather than propulsion.

neuroscience↗