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Should the Equilibrium Point Hypothesis (EPH) Be Considered a Scientific Theory?

Robert L. Sainburg

The purpose of this commentary is to discuss factors that limit consideration of the equilibrium point hypothesis as a scientific theory. The EPH describes control of motor neuron threshold through the variable lambda, which corresponds to a unique referent configuration for a muscle, joint, or combination of joints. One of the most compelling features of the equilibrium point hypothesis is the integration of posture and movement control into a single mechanism. While the essential core of the hypothesis is based upon spinal circuitry interacting with peripheral mechanics, the proponents have extended the theory to include the higher-level processes that generate lambda, and in doing so, imposed an injunction against the supraspinal nervous system modeling, computing, or predicting dynamics. This limitation contradicts evidence that humans take account of body and environmental dynamics in motor selection, motor control, and motor adaptation processes. A number of unresolved limitations to the EPH have been debated in the literature for many years, including whether muscle resistance to displacement, measured during movement, is adequate to support this form of control, violations in equifinality predictions, spinal circuits that alter the proposed invariant characteristic for muscles, and limitations in the description of how the complexity of spinal circuitry might be integrated to yield a unique and stable equilibrium position for a given motor neuron threshold. In addition, an important empirical limitation of EPH is the measurement of the invariant characteristic, which needs to be done under a constant central state. While there is no question that the EPH is an elegant and generative hypothesis for motor control research, the claim that this hypothesis has reached the status of a scientific theory is premature.

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Introduction to the Special Z-Issue in Honor of the 90th Birthday of Vladimir M. Zatsiorsky

Mark L. Latash

primarily in the field of biomechanics, and I performed studies of human motor control and movement disorders in neurological patients. Vladimir’s interest toward the field of the neural control of movement can be traced back to the mid-1960s when he met Nikolai Bernstein and also developed interactions

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The Role of Imitation, Primitives, and Spatial Referent Coordinates in Motor Control: Implications for Writing and Reading

Shelia Guberman and Mark L. Latash

The main goal of this paper is to unite intuitive ideas, such as the imitation principle ( Bongard, 1970 ) and the idea of building blocks (primitives, reviewed in Latash, 2020b ) for complex skills, with the theory of the neural control of movement with spatial referent coordinates (RCs; reviewed

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The Influence of Recent Actions and Anticipated Actions on the Stability of Finger Forces During a Tracking Task

Mitchell Tillman and Satyajit Ambike

, mechanisms, and functions . Journal of Neurophysiology, 120 ( 1 ), 88 – 104 . PubMed ID: 29589812 doi:10.1152/jn.00084.2018 10.1152/jn.00084.2018 Latash , M.L. , & Huang , X. ( 2015 ). Neural control of movement stability: Lessons from studies of neurological patients . Neuroscience, 301, 39

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Intramuscle Synergies: Their Place in the Neural Control Hierarchy

Mark L. Latash, Shirin Madarshahian, and Joseph M. Ricotta

some of the reviewed findings and try to draw conclusions that would be potentially important for the current understanding of the neural control of movement. The observations of two patterns of the loading factors at the stage of MU-mode identification based on MUs combined over the flexor and

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Optimality, Stability, and Agility of Human Movement: New Optimality Criterion and Trade-Offs

Mark L. Latash

based on two important developments. The first is the theory of the neural control of movement with time-varying spatial referent coordinates (RC) for the involved effectors (reviewed in Feldman, 2015 ; Latash, 2010 , 2019 , 2021b ), which is based on the classical equilibrium point hypothesis