An apparatus for characterization and control of isolated muscle

Farahat, Waleed A.; Herr, Hugh M.

doi:10.1109/tnsre.2005.857686

Cited by 11 publications

(12 citation statements)

References 40 publications

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“…However, these studies provide little insight into the origins of cyclic steady-state behavior or the role of limb geometry in its emergence (42,43). In recent years, advances in robotics, controls, and instrumentation have made it possible to explore the coupling between environmental dynamics and muscle-tendon architecture/limb geometry in isolated muscle experiments like never before (44,45). A bio-robotic approach has been used in studies designed to optimize the interaction of antagonist muscle pairs for power output when working against a load of known resonant frequency (the calculation of which did not include passive muscle stiffness), as well as to identify the fundamental limits on power output imposed by muscle actuator properties and limb geometry during a single propulsive swimming stroke (46,47).…”

Section: Significancementioning

confidence: 99%

Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion

Robertson

Sawicki

2015

Proc. Natl. Acad. Sci. U.S.A.

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In terrestrial locomotion, there is a missing link between observed spring-like limb mechanics and the physiological systems driving their emergence. Previous modeling and experimental studies of bouncing gait (e.g., walking, running, hopping) identified muscletendon interactions that cycle large amounts of energy in series tendon as a source of elastic limb behavior. The neural, biomechanical, and environmental origins of these tuned mechanics, however, have remained elusive. To examine the dynamic interplay between these factors, we developed an experimental platform comprised of a feedback-controlled servo-motor coupled to a biological muscletendon. Our novel motor controller mimicked in vivo inertial/gravitational loading experienced by muscles during terrestrial locomotion, and rhythmic patterns of muscle activation were applied via stimulation of intact nerve. This approach was based on classical workloop studies, but avoided predetermined patterns of muscle strain and activation-constraints not imposed during real-world locomotion. Our unconstrained approach to position control allowed observation of emergent muscle-tendon mechanics resulting from dynamic interaction of neural control, active muscle, and system material/inertial properties. This study demonstrated that, despite the complex nonlinear nature of musculotendon systems, cyclic muscle contractions at the passive natural frequency of the underlying biomechanical system yielded maximal forces and fractions of mechanical work recovered from previously stored elastic energy in seriescompliant tissues. By matching movement frequency to the natural frequency of the passive biomechanical system (i.e., resonance tuning), muscle-tendon interactions resulting in spring-like behavior emerged naturally, without closed-loop neural control. This conceptual framework may explain the basis for elastic limb behavior during terrestrial locomotion.muscle-tendon mechanics | elastic limb behavior | neural control | resonance | terrestrial locomotion E lastic limb behavior is a hallmark of terrestrial locomotion; the mechanics can be described by the physics of spring-mass interaction (1-4). Simple models that treat the entire leg as a linear spring loaded inverted pendulum (SLIP), and the body as a point mass can predict the mechanics of hopping (3), walking (4), and running (1, 4), as well as more subtle features of gait like the importance of swing-leg retraction for dynamic stability (5, 6). This simplified mechanical framework for describing whole limb behavior has led to breakthroughs in understanding of control targets in both biological locomotion (7) and bio-inspired walking robots (8, 9).Although these mechanics are simple conceptually, understanding how they emerge from a biological limb has proven to be a far greater challenge. Every skeletal muscle exhibits nonlinear excitation-contraction coupling (10), nonlinear dependence of active muscle force on fascicle strain (11) and rate of strain (12), nonlinear force-displacement dynamics in tendon (13) and p...

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Section: Significancementioning

confidence: 99%

Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion

Robertson

Sawicki

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…The force produced by stacked LCEs was measured on an apparatus with a load sensor under isometric conditions [20]. The LCE stack was first mounted in a fixed clamp with the heating element attached to a power supply lead.…”

Section: Stack Testingmentioning

confidence: 99%

Stacking nematic elastomers for artificial muscle applications

Spillmann

Naciri

Martin

et al. 2007

Sensors and Actuators A: Physical

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“…A full description of the experimental platform and techniques can be found in [25]. For the benefit of the reader, we provide a brief description here.…”

Section: Methodsmentioning

confidence: 99%

Optimal Workloop Energetics of Muscle-Actuated Systems: An Impedance Matching View

Farahat

Herr

2010

PLoS Comput Biol

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Integrative approaches to studying the coupled dynamics of skeletal muscles with their loads while under neural control have focused largely on questions pertaining to the postural and dynamical stability of animals and humans. Prior studies have focused on how the central nervous system actively modulates muscle mechanical impedance to generate and stabilize motion and posture. However, the question of whether muscle impedance properties can be neurally modulated to create favorable mechanical energetics, particularly in the context of periodic tasks, remains open. Through muscle stiffness tuning, we hypothesize that a pair of antagonist muscles acting against a common load may produce significantly more power synergistically than individually when impedance matching conditions are met between muscle and load. Since neurally modulated muscle stiffness contributes to the coupled muscle-load stiffness, we further anticipate that power-optimal oscillation frequencies will occur at frequencies greater than the natural frequency of the load. These hypotheses were evaluated computationally by applying optimal control methods to a bilinear muscle model, and also evaluated through in vitro measurements on frog Plantaris longus muscles acting individually and in pairs upon a mass-spring-damper load. We find a 7-fold increase in mechanical power when antagonist muscles act synergistically compared to individually at a frequency higher than the load natural frequency. These observed behaviors are interpreted in the context of resonance tuning and the engineering notion of impedance matching. These findings suggest that the central nervous system can adopt strategies to harness inherent muscle impedance in relation to external loads to attain favorable mechanical energetics.

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An apparatus for characterization and control of isolated muscle

Cited by 11 publications

References 40 publications

Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion

Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion

Stacking nematic elastomers for artificial muscle applications

Optimal Workloop Energetics of Muscle-Actuated Systems: An Impedance Matching View

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