Muscle is the prime mover of animal locomotion, but muscle force is not usually equal to output force. Instead, the instantaneous ratio between output and input force (the mechanical advantage, MA) is modulated by intervening skeletal elements. Traditional functional analysis, focussing on the instantaneous action of gearing, suggests that smaller MA favours speed, while larger MA favours force. However, mounting evidence suggests that this perspective is too simplistic when considering the outcome of a dynamic muscle contraction. We approach this problem systematically by introducing an analytical framework to study the effect of gearing. This framework reveals two mechanisms by which the output speed of a contraction is affected by gearing. First, gearing can limit muscle work output, because it is bound not only by muscle displacement, but also by muscle shortening velocity. Second, it controls how each unit of muscle work is partitioned into system energies (e.g. kinetic energy vs heat). Consequently, smaller gear ratios do not always result in larger output speeds. No single optimal gear ratio exists for any organism, but rather the optimum depends on internal muscle properties and contraction dynamics, as well as external forces. The analytical framework we propose provides a blueprint to determine optimality conditions across muscle physiology, anatomy, mechanical environment and size, and so to investigate form-function relationships in musculoskeletal gearing.

Musculoskeletal gearing for maximum speed: analytic optimization across mechanical environment and size.

The ability to perform sit-to-stand (STS) behaviours is fundamental for humans and other animals, yet the underlying high-level control goal driving the selection of a specific movement pattern for the STS transition remains elusive. Exploring the STS transition in non-human animals, particularly birds, offers an opportunity to deepen this understanding and allows for an independent assessment of how body sizes influence performance criteria. Computational biomechanical modelling and simulation, combined with optimal control methods, provide a rigorous and mechanistic approach to address these questions, offering insights that experimental limitations may hinder. Drawing inspiration from human studies, we systematically evaluate STS performance criteria (e.g., minimisation of effort and the muscle force rate) and examine how these criteria vary with body sizes, using a simplified two-link model to simulate vertical movements. We use this simplified simulation to inform fully predictive, three-dimensional, muscle-driven simulations of the STS transition in the emu (Dromaius novaehollandiae), a large bipedal bird. This study, focusing on emus, provides insights into avian species’ control strategies during the STS transition, with future investigations extending to simulate this transition in other bird species, contributing not only to our understanding of organismal morphofunctional specialisation but also to applications in robotics, prosthetics, and animal welfare, as well as aiding in the reconstruction of locomotion in extinct species.

Predictive simulations of musculoskeletal function and sit-to-stand performance in a large bipedal bird - the emu (Dromaius novaehollandiae)

Muscle properties such as strength and stiffness vary between species, joints, and age groups, but how these parameters interact to affect locomotor performance can be difficult to assess in complex models. To address this issue, we developed a simplified model of a single joint with two antagonistic Hill-type muscles, and varied the associated muscle parameters combinatorially over a large range. For a given parameter combination, we found optimal joint movements that minimized movement time while starting and ending at rest. The reduction of force, maximum contraction velocity and activation rate all had detrimental effects on performance, independent of other parameters. In contrast, over the large parameter space, deactivation and passive stiffness had no effect on performance on their own, but pronounced interactive effects with eachother. Increasing stiffness reduced joint movement time at fast deactivation rates, but increased movement time at low deactivation rates. This occurs because antagonist muscles resist the passive tension at rest, but are stretched eccentrically by the agonist, amplifying their active resistive force. Fast-deactivating muscles can avoid this resistive effect, allowing the passive stiffness to amplify accelerating force and enhance performance. Our results suggest that ameliorating muscle deactivation with age could be explored as a potential therapeutic target to enhance rapid motion, and that fast deactivation of muscle may be an important functional trait in animals using ballistic movements.

Interaction of muscle parameters on ballistic joint movement - implications for ageing and comparative locomotion

The lateral sequence walk is a widespread gait among mammals, but certain groups, such as adult primates and aardvarks, instead employ a diagonal sequence gait. It may be that caudally-shifted centers of mass and large whole-body moments of inertia in the latter groups make diagonal sequence gaits energetically favourable. To test this, we built a simple model of a generalized quadruped in OpenSim, consisting of two-link, four degree-of-freedom legs, and a two-link trunk with a spinal joint. We generate gaits to minimize various measures of effort cost, including torque-rate squared and joint work, by employing recent advances in trajectory optimization with algorithmic differentiation. We show how mass distribution affects gait choice in three dimensions, and compare these results to the gaits of various mammalian groups.

Effect of mass distribution on effort-optimizing gait in a 3D model

You can leave your comments for the author. Authors will get notified and will reply asynchronously.

Animal Poster Session                                                                

poster

You need to log in with the email address you registered with. Access credentials have been sent to your email. 

Please be sure to check your spam and other email folders if you do not see an email confirmation right away.

Please log in to explore this event.

If you see this page it means you are not logged in or registered.

If you feel like you see this message by mistake please make sure you are logged in with the email you registered with.

If you are not registered yet, you can do so [**here**](https://www.sebiology.org/events/seb-conference-prague-2024/registration2024.html). 

Please login or register

SEB Conference Prague 2024

SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

Biomechanics is the study of mechanical principles and function of biological systems, ranging from the molecular to the organismal level, and beyond, including interactions with the environment. As such, the SEB Biomechanics Group brings together scientists from a wide range of disciplines, including zoologists, botanists, molecular biologists, physiologists, kinesiologists, mathematicians, engineers, biomimeticists, and computer scientists.

The SEB Annual Conference showcases Biomechanics presentations in a podium presentation session and poster sessions on the application of biomechanics to any topic, including swimming, flying, terrestrial locomotion, feeding, functional morphology, muscle-tendon mechanics, damage and repair of materials, in animals and plants. We also run special topic sessions with recent foci including food processing across animals, mechanics of mechanoreception, and biomechanics in the wild.

**Session Organiser:** Dr. Nicolai Konow


A21 - Biomechanics

technical paper

[![](https://assets.underline.io/uploads/markdown_image/1/image/98d8e5171b4f8a63004e3ed7d2a31398.png)](https://us06web.zoom.us/rec/play/DDZVQIbNRQPkIv6DZW9qt3dqwFx_jiexHxt4QHPjL2GAS2qUNdxL2R2w2jEwqgbVqyeqory2Pjgtqend.QIiKM0iZ19Oe6nI1?autoplay=true&startTime=1657176786000) 
Robotic models can provide new insights into how animals use musculoskeletal systems to move through their environment. These biological motors drive crucial physiological, behavioural—and ultimately ecological and evolutionary—processes. But the complexity of interacting muscles and skeletal elements limits what we can directly observe and measure. Replicating aspects of these biological systems with robotic mechanisms lets us test new hypotheses and explore biologically inspired design applications. This session brings together a diverse set of researchers exploring new ways to implement and apply musculoskeletal robotics.

A4: Muscles & Motors: Organismal bioinspired robotics

Discover the art of creating extraordinary science at SEB’s Annual Conference at Le Corum Conference Center in Montpellier, France from 5 to 8 July 2022.

SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years.

It looks like you are not registered for this event. 


To access the site, please log in using the email address you registered with or in case you are not yet registered, you can still register [here](https://www.sebiology.org/events/seb-annual-conference-2022/registration.html).



Please register!

SEB Annual Conference 2022

2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years - Montpellier, France

Delyle Polet

4

2

Presentations

Musculoskeletal gearing for maximum speed: analytic optimization across mechanical environment and size.

Predictive simulations of musculoskeletal function and sit-to-stand performance in a large bipedal bird - the emu (Dromaius novaehollandiae)

Interaction of muscle parameters on ballistic joint movement - implications for ageing and comparative locomotion

Effect of mass distribution on effort-optimizing gait in a 3D model

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES