Biology subjects

Rainbow, M. J.

Publications and source records attributed to Rainbow, M. J..

6 recordsLinked to original sources

bioRxiv2024

The Trade-Off Between Torque and Power with Speed: A Study of Shoulder Performance During an Isokinetic and Multiplanar Task

The human shoulder likely evolved under selective pressures favouring diverse tasks that require high mobility, speed, and torque. For example, humans are uniquely adept at high-speed and accurate throwing. Prior work has aimed to quantify the kinematics and kinetics of upper limb movements in isometric or uniplanar motions. However, we still do not fully understand the trade-offs of shoulder torque and power with angular velocity during functional tasks that are reflective of demands that may be relevant to the shoulders evolution. We developed a novel approach for upper limb 3D inverse dynamic calculations by integrating motion capture with an instrumented cable machine. Twenty-five participants performed a crossbody, isokinetic upper limb motion at various cable speeds in a rigid and free torso condition (self-imposed). Shoulder torque decreased significantly (p < 0.05) with increasing angular velocity in 19 and 16 participants for the constrained and unconstrained conditions, respectively. Shoulder power increased significantly (p < 0.05) with angular velocity for 6 and 11 participants for constrained and unconstrained, respectively. T-tests revealed no statistical difference between the torso conditions for torque and power against angular velocity. Our findings suggest that despite having a trade-off in torque and velocity, the shoulder may be tuned to produce power over a wide range of velocities independent of energy transfer from the lower extremities.

physiology↗

bioRxiv2024

Sexual dimorphism and allometry in human scapular morphology

Scapular morphology is highly variable across the human population and appears to be sexually dimorphic - differing significantly between males and females. However, previous investigations of sexual dimorphism in scapula shape have not considered the effects of allometry (the relationship between size and shape). Disentangling allometry from sexual dimorphism is necessary because apparent sex-based differences in morphology could be due to inherent differences in body size. This study aimed to investigate sexual dimorphism in scapula shape and examine the role of allometry in sex-based variation. We used three-dimensional geometric morphometrics with Procrustes ANOVA to quantify scapula shape variation associated with sex and size in 125 scapulae. Scapular morphology significantly differed between males and females, and males tended to have larger scapulae than females for the same body height. We found that males and females exhibited distinct allometric relationships, and sexually dimorphic shape changes did not align with male- or female-specific allometry. A secondary test revealed that sexual dimorphism in scapula shape persisted between males and females of similar body heights. Overall, our findings indicate that sex-based differences in scapular shape are independent of size-shape relationships. Our results shed light on the potential role of sexual selection in human shoulder evolution, present new hypotheses for biomechanical differences in shoulder function between sexes, and identify relevant traits for improving sex classification accuracy in forensic analyses.

bioengineering↗

bioRxiv2024

Mitigating Stress: Exploring how our feet change shape with size

If human skeletal shape increases proportionally with size (isometric scaling) this can produce exponential increases in joint contact stresses. However, if skeletal shape changes as a function of size (allometric scaling) this can mitigate increases in joint contact stress by changing the surface area to volume ratio. Here we explored whether human foot bones scale with allometry and, if so, to identify the shape features that are associated with bone size. Computed tomography scans of the two largest foot bones (talus, calcaneus) were obtained from 36 healthy individuals. We implemented a scaling analysis for each joint surface area and bone. We performed a Procrustes ANOVA to establish the shape features associated with bone size. In line with our hypothesis, articular surfaces on the talus and the posterior facet of the calcaneus all scaled with positive allometry. Interestingly, the calcaneus scaled with negative allometry, appearing more cube-like with increasing size. This may be important for mitigation of internal bone stresses with increasing skeletal size. Our findings suggest distinct, but varied scaling strategies within the foot. This may reflect the requirement to maintain healthy joint contact and internal bone stresses with increasing size.

evolutionary biology↗

bioRxiv2023

Reassessing the role of foot power in human gait

The foot acts as the primary interface to the ground during bipedal locomotion. It absorbs and returns energy over stance as the longitudinal arch deforms and recoils. The term arch recoil evokes the concept that the foots returned energy directly propels the centre of mass forward by lifting the talus. However, recent work has shown that arch recoil does not directly drive the body forward; instead, it lowers and posteriorly tilts the talus, putting it into a more favourable position for upright gait. Here, we aim to supply a kinetic explanation for this mechanism. We applied the unified deformable power approach to highly accurate talus kinematics from biplanar videoradiography and force plate measurements to measure the power absorbed/produced by the foot. We coupled these measurements with a simple mathematical model that allowed us to restrict rotation and linear actuation of the talus caused by the recoil of the arch to demonstrate that positive foot power primarily contributes to posteriorly tilting the talus. This suggests the role of positive foot power during propulsion is to keep the talocrural surface in a more favourable position for upright gait rather than directly propelling the centre of mass forwards. These findings highlight that arch mobility during push-off is critical for allowing the ankle to directly propel the body forward and upward during the propulsive phase of gait.

physiology↗

bioRxiv2022

Mobility of the human foot's medial arch enables upright bipedal locomotion

Developing the ability to habitually walk and run upright on two feet is one of the most significant transformations to have occurred in human evolution. Many musculoskeletal adaptations enabled bipedal locomotion, including dramatic structural changes to the foot and, in particular, the evolution of an elevated medial arch (H. Elftman and Manter, 1935). The foots arched structure has previously been assumed to play a central role in directly propelling the centre of mass forward and upward through leverage about the toes (Herbert Elftman and Manter, 1935) and a spring-like energy recoil (Hicks, 1955). Paradoxically, these roles seemingly require either arch rigidity (for the former) or mobility (for the latter). However, it is unclear whether or how the mobility and height of the medial arch support its propulsive lever function. Here we show, using high-speed biplanar x-ray, that regardless of intraspecific differences in medial arch height, arch recoil enables a longer contact time and favourable propulsive conditions for walking upright on an extended leg. This mechanism presumably helped drive the evolution of the longitudinal arch after our last common ancestor with chimpanzees, who lack this mobility during push-off. We discovered that the previously overlooked navicular-medial cuneiform joint is primarily responsible for this mobility in human arches, suggesting that future morphological investigations of this joint will provide new interpretations of the fossil record. Our work further suggests that enabling the mobility of the longitudinal arch in footwear and surgical interventions is critical for maintaining the ankles natural propulsive ability.

physiology↗

bioRxiv2020

Co-contraction uses dual control of agonist-antagonist muscles to improve motor performance

Co-contraction of agonist-antagonist muscles is commonly observed when performing difficult motor tasks. The benefit of co-contraction is thought to be zero-delay corrections to unexpected disturbances from increased intrinsic muscle impedance. We used upper-limb postural and tracking tasks to characterize the effects of co-contraction on motor corrections to loads applied to the limb. We systematically controlled pre-perturbation muscle activity and showed that co-contraction improves subsequent corrective responses in both tasks. However, substantial improvements in the corrective response are only observed at the time when neural feedback pathways can also contribute. We demonstrate that muscle impedance appears to play a minor role in improving performance. Instead, co-contraction engages a dual agonist-antagonist control strategy to counter disturbances, that is distinct from the control strategy used when not co-contracting or selectively pre-activating a single muscle group. Critically, we showed that this dual agonist-antagonist control strategy improved performance even at low levels of co-contraction.

neuroscience↗