Muscle is the universal agent of animal movement, and limits to muscle performance are therefore an integral aspect of animal behaviour, ecology, and evolution. A mechanical perspective on movement makes it amenable to analysis from first principles, and so brings the seeming certitude of simple physical laws to the challenging comparative study of complex biological systems. Early contributions on movement biomechanics considered muscle energy output to be limited by muscle work capacity, Wmax; triggered by seminal work in the late 1960s, it is now held broadly that a complete analysis of muscle energy output is to also consider muscle power capacity, for no unit of work can be delivered in arbitrarily brief time. Here, we adopt a critical stance towards this paradigmatic notion of a power-limit, and argue that the alternative constraint to muscle energy output is instead imposed by a characteristic kinetic energy capacity, Kmax, dictated by the maximum speed with which the actuating muscle can shorten. The two critical energies can now be directly compared, and define the physiological similarity index, Γ=Kmax/Wmax. It is the explanatory power of this comparison that lends weight to a shift in perspective from muscle power to kinetic energy capacity, as is argued through a series of brief illustrative examples. Γ emerges as an important dimensionless number in musculoskeletal dynamics, and sparks novel hypotheses on functional adaptations in musculoskeletal “design” that depart from the parsimonious evolutionary null hypothesis of geometric similarity.
Beyond power limits: the kinetic energy capacity of skeletal muscle
Call for Papers: The Integrative Biology of the Gut. Guest Editors Carol Bucking, Matt Regan and John Terblanche
We are pleased to welcome submissions for our upcoming Special Issue: The Integrative Biology of the Gut . We are calling for forward-looking papers that address the functional roles of the gut. We will consider papers that address gut function from the cellular level to its interactions with other organs and tissues, including its role in diverse ecophysiological processes, spanning both vertebrate and invertebrate species. The deadline for submission to this issue is 1 October 2024.
Extraordinary creatures: notothenioids and icefish
In our new Conversation focusing on extraordinary creatures, Christina Cheng and Kristin O'Brien tell us about the remarkable freeze tolerant nototheniods that live in the waters around Antarctica and how icefish are the only adult vertebrates that survive without haemoglobin.
Why are microclimates essential for predicting climate change responses and how to measure them?
In their Commentary, Duncan Mitchell and colleagues discuss problems with predicting terrestrial animals’ responses to a warming world based on air temperature, rather than the microclimate of their thermal environment. They provide a simple, low-cost approach to microclimate measurements to provide a more realistic assessment of terrestrial animal performance and predicted population responses in hot regions under warming conditions. This approach requires measuring the variables involved in the exchange of heat and water vapour between animals and their environment.
Turkey vultures defy thin air by flying faster
Turkey vultures successfully fly at high altitude despite the challenge of generating lift in thin air, but how? Jonathan Rader & Ty Hedrick discovered that the birds fly 1m/s faster at 2200m than at sea level to generate sufficient lift to remain aloft.
Biologists @ 100 - join us in Liverpool in March 2025
We are excited to invite you to a unique scientific conference, celebrating the 100-year anniversary of The Company of Biologists, and bringing together our different communities. The conference will incorporate the Spring Meetings of the BSCB and the BSDB, the JEB Symposium Sensory Perception in a Changing World and a DMM programme on antimicrobial resistance. Find out more and register your interest to join us in March 2025 in Liverpool, UK.
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