Force variability is mostly not motor noise: Theoretical implications for motor control
Abstract
Variability in muscle force is a hallmark of healthy and pathological human behavior. Predominant theories of sensorimotor control assume ‘motor noise’ leads to force variability and its ‘signal dependence’ (variability in muscle force whose amplitude increases with intensity of neural drive). Here, we demonstrate that the two proposed mechanisms for motor noise (i.e. the stochastic nature of motor unit discharge and unfused tetanic contraction) cannot account for the majority of force variability nor for its signal dependence. We do so by considering three previously underappreciated but physiologically important features of a population of motor units: 1) fusion of motor unit twitches, 2) coupling among motoneuron discharge rate, cross-bridge dynamics, and muscle mechanics, and 3) a series-elastic element to account for the aponeurosis and tendon. These results argue strongly against the idea that force variability and the resulting kinematic variability are generated primarily by ‘motor noise.’ Rather, they underscore the importance of variability arising from properties of control strategies embodied through distributed sensorimotor systems. As such, our study provides a critical path toward developing theories and models of sensorimotor control that provide a physiologically valid and clinically useful understanding of healthy and pathologic force variability.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 08, 2021
- Source ID
- 10.1371/journal.pcbi.1008707
Entities
People
- Akira Nagamori
- Christopher M. Laine
- Francisco J Valero-Cuevas
- Gerald E. Loeb
Organizations
- Defense Advanced Research Projects Agency
- National Institute of Arthritis and Musculoskeletal and Skin Diseases
- National Institute of Neurological Disorders and Stroke
- United States Department of Defense