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Functional Neurology
Published in James Crossley, Functional Exercise and Rehabilitation, 2021
The challenge posed by the fact that the motor system has so many options to choose from is referred to as the ‘degrees of freedom problem’. Creating a new motor strategy from scratch each and every time we decide to move creates a huge ‘computational load’. There are far too many calculations to make and factors to consider when deciding how to move. The brain lacks the time or capacity to create movement strategies on the fly. It needs to take shortcuts.
Stages of motor learning
Published in Andrea Utley, Motor Control, Learning and Development, 2018
According to Bernstein (1967), the learning of a motor skill can be likened to the solving of a problem; the problem being how best to harness the many available degrees of freedom of the human movement system. Degrees of freedom are all the available muscles, joints, tendons and ligaments of the human body which are free to vary and thus must be controlled for purposeful movement, which gave rise to Bernstein’s (1967) degrees of freedom problem.
Exploring the perceptual-motor workspace: New approaches to skill acquisition and training
Published in Youlian Hong, Roger Bartlett, Routledge Handbook of Biomechanics and Human Movement Science, 2008
Chris Button, Jia-Yi Chow, Robert Rein
Humans acquire skill by consistently coordinating relevant parts of the body together into functional synergies, for example when performing a triple salko jump in ice skating or, more mundanely, when stepping on to a surface. The search for simplistic laws of cause and effect has meant that movement scientists have often struggled to come to terms with the complexity humans must overcome to produce such skilled actions. This issue has become known as Bernstein’s (Bernstein, 1967) ‘degrees of freedom problem’. Degrees of freedom (DoF) refer to the independent components in the performer that can fit together in many different and redundant ways. For example, the large number of available muscles, joints, limb segments and bones of a human body exemplify parts of the DoF of the human motor system.
Female Athletes Exhibit Greater Trial-to-Trial Coordination Variability When Provided with Instructions Promoting an External Focus
Published in Journal of Motor Behavior, 2022
Lindsey Waite, Molly Stewart, Kanikkai Steni Balan Sackiriyas, Jithmie Jayawickrema, Thomas Gus Almonroeder
In general, the observation of greater trial-to-trial coordination variability for the external focus condition seems to be consistent with what would be predicted based on the ‘constrained action hypothesis’ proposed by Wulf and colleagues (Wulf, 2007). The constrained action hypothesis posits that when an individual focuses on a specific aspect of their movement (e.g. the position/motion of their knees), it limits (or ‘constrains’) the automatic control processes that govern movement. Whereas when an individual focuses more generally on the outcome(s) of their movement (e.g. the impact forces produced during landing), there is greater freedom for the motor control system to explore different kinematic solutions in an attempt to identify a more optimal way to achieve the desired outcome and solve the degrees of freedom problem (typically resulting in better performance). This appeared to play out in the case of this study, as subjects varied more from trial-to-trial in how they coordinated their lower body joints during landing when given instructions promoting an external focus, which would seem to suggest they were actively exploring a wider range of motor control strategies, compared to when they were given more explicit instructions about how to modify their landing pattern.
Collective Variables and Task Constraints in Movement Coordination, Control and Skill
Published in Journal of Motor Behavior, 2021
Collective variables, in terms of order parameters of macroscopic movement phenomena, were given a formal and explicit place in the coordination dynamics of the HKB model (Haken et al., 1985). Yet, in spite of the many experiments inspired by the dynamical systems approach to the study of movement in action over the last 35 years, there has not been a proportionate theoretical or experimental examination of collective variables, and their proposed informational character (Kelso, 1994; Mitra et al., 1998). Moreover, and relatedly, the postulation of reciprocal causality (Kelso, 1995), and the associated notion of time scale separation, have not been experimentally tested in the movement domain in spite of its centrality to the coordination dynamics framework. Our intuition is that the notion of collective variables is a relevant theoretical postulation in regard to the degrees of freedom problem (Bernstein, 1967) but that it is difficult to implement experimental tests of its implications in the context of motor learning and control.
Do Tangential Finger Forces Utilize Mechanical Advantage During Moment of Force production?
Published in Journal of Motor Behavior, 2021
Junkyung Song, Kitae Kim, Jaebum Park
With respect to end-effector force generation and sharing among a redundant set of effectors, the principle of MA is one way to resolve the degrees of freedom problem (Park et al., 2012; Zatsiorsky & Latash, 2008)—not by finding a unique combination of outcome levels of the involved variables (Todorov et al., 2005)—but by conjugating an abundant set of variables (i.e., motor abundance, see Latash, 2012; Reschechtko et al., 2015 ) based on the rule of organizing sharing and co-variation patterns among the variables. The normal components of finger forces with larger moment arms had larger contributions to the required torque during prismatic grasps using hand digits (Park et al., 2012; Shim et al., 2004; Zatsiorsky et al., 2003b). In particular, the MAs of the index and little fingers are relatively large compared to the middle and ring fingers during prismatic grasping or pressing. This is because of the partially constrained neutral line of the hand, i.e., the line where a zero net moment is observed is likely positioned along the ulnar side of the middle finger (Zatsiorsky & Latash, 2008). Hence, the anatomical structure of the body segment, such as the parallel alignments of fingers, is assumed to be a primary factor for differentiating the MAs of multiple elements related to their sharing strategies when the normal component of finger forces is considered.