Latch-mediated spring actuation (LaMSA): the power of integrated biomechanical systems

Abstract

Across the tree of life – from fungi to frogs – organisms wield small amounts of energy to generate fast and potent movements. These movements are propelled with elastic structures, and their loading and release are mediated by latch-like opposing forces. They comprise a class of elastic mechanisms termed latch-mediated spring actuation (LaMSA). Energy flow through LaMSA begins when an energy source loads elastic element(s) in the form of elastic potential energy. Opposing forces, often termed latches, prevent movement during loading of elastic potential energy. As the opposing forces are shifted, reduced or removed, elastic potential energy is transformed into kinetic energy of the spring and propelled mass. Removal of the opposing forces can occur instantaneously or throughout the movement, resulting in dramatically different outcomes for consistency and control of the movement. Structures used for storing elastic potential energy are often distinct from mechanisms that propel the mass: elastic potential energy is often distributed across surfaces and then transformed into localized mechanisms for propulsion. Organisms have evolved cascading springs and opposing forces not only to serially reduce the duration of energy release, but often to localize the most energy-dense events outside of the body to sustain use without self-destruction. Principles of energy flow and control in LaMSA biomechanical systems are emerging at a rapid pace. New discoveries are catalyzing remarkable growth of the historic field of elastic mechanisms through experimental biomechanics, synthesis of novel materials and structures, and high-performance robotics systems.

Controlling jumps through latches in small jumping robots

“…Jumping with springs, and more generally using springs as actuators, is described in the latchmediated spring actuation (LaMSA) framework [22,23]. A generic LaMSA system has a spring that is loaded and then released by a latch to power a movement.…”

Beyond power limits: the kinetic energy capacity of skeletal muscle

“…FVPs are also often invoked to explain a key functional benefit of the in-series elasticity introduced by tendons: in dynamic contractions, tendons can decouple limb and muscle shortening speed, and muscle can consequently achieve similar absolute limb speeds with lower muscle shortening speeds, so increasing the average force and power (Aerts, 1997;Astley and Roberts, 2012;Farris et al, 2016;Kurokawa et al, 2001;Marsh, 2022;Roberts and Marsh, 2003;Robertson et al, 2018); in quasi-static "latched" contractions, muscle can contract arbitrarily slowly against elastic elements, and so avoid both forcevelocity-effects and supposed muscle power limits to performance, before explosively releasing the stored energy (Bennet-Clark, 1975;Bennet-Clark and Lucey, 1967;Gronenberg, 1996;Longo et al, 2019;Patek, 2023). A large body of careful work has been dedicated to such amplification of muscle power via in-series elastic elements, be it in dynamic or in "latched" quasi-static contractions (for recent reviews, see Holt and Mayfield, 2023;Longo et al, 2019;Patek, 2023). There is no doubt, of course, that elastic elements can amplify muscle power.…”

“…Because jumping performance in small animals is likely limited by the kinetic energy capacity of muscle, we suggest that (i) their springs are "work enablers", allowing them to overcome the constraint on energy output imposed by a limiting kinetic energy capacity; and (ii) that power amplification is an epiphenomenon instead of the biological purpose of inseries elasticity. The outcome of this somewhat semantic debate is clearly immaterial for the validity of the long list of fundamental insights that have been derived from the study of power amplification due to biological "springs" (Gronenberg, 1996;Ilton et al, 2018;Longo et al, 2019;Patek, 2023).…”

“…No muscle contraction can violate these limits, and they are consequently thought to pose universal constraints on animal performance. A limiting work or power density have, in some form or another, been invoked to account for a remarkable diversity of non-trivial observations across the broad field of comparative animal biomechanics, including the maximum running speed (e. g. Hill, 1950b;Irschick et al, 2003;Meyer-Vernet and Rospars, 2015;Usherwood and Gladman, 2020), flight speed (Alexander, 2005;Pennycuick, 1968), swimming speed (e. g. Clemente and Federle, 2012;O'dor and Webber, 1991;Richards and Clemente, 2013;Richards and Sawicki, 2012;Wakeling and Johnston, 1998), and jump height (e. g. Bennet-Clark, 1977;Gabriel, 1984;Lutz and Rome, 1994;Marsh, 1994;Sutton et al, 2016;Wilson and James, 2000); size-specific variations in animal posture (Usherwood, 2013); the prevalence of latched "power-amplifiers" in small animals (Alexander, 1988;Bennet-Clark, 1975;Gronenberg, 1996;Ilton et al, 2018;Longo et al, 2019;Patek, 2023); the mechanical benefits of in-series elasticity in explosive muscle contractions (e. g. Aerts, 1997;Alexander, 1995;Galantis and Woledge, 2003;Hill, 1950a;James et al, 2007;Lichtwark and Wilson, 2005;Mendoza and Azizi, 2021;Peplowski and Marsh, 1997;Roberts, 2016;Roberts and Marsh, 2003;Rosario et ...…”

“…Both muscle power and work density appear to be remarkably conserved -they vary by at most one order of magnitude across animal size, ecological niche, and evolutionary history (Askew and Marsh, 2002;Close, 1972;Marden and Allen, 2002;Medler, 2002;Rospars and Meyer-Vernet, 2016). Animal size is however thought to determine whether it is the work or the power density that limits the energy output during impulsive muscle contractions (e. g. Alexander, 2003;Bennet-Clark, 1977;Biewener and Patek, 2018;Gabriel, 1984;Ilton et al, 2018;Longo et al, 2019;Patek, 2023;Schmidt-Nielsen, 1984;Usherwood, 2013;Usherwood and Gladman, 2020). Power is the amount of work done per time, and smaller animals are thought to have less time to complete muscle contractions (Alexander, 2003;Bennet-Clark, 1977;Biewener and Patek, 2018;Schmidt-Nielsen, 1984).…”