Change in the Organization of Degrees of Freedom With Learning

Do Bernstein's Stages of Learning Apply after Stroke? A Scoping Review on the Development of Whole-Body Coordination after Cerebrovascular Accidents

Stroke is one of the leading causes of disability around the world, presenting unique challenges in motor development during the rehabilitation process. Based on studies in movement and sports science, thorough knowledge has accumulated on the development of movement skills. Through the works of Nikolai Bernstein, it has been established that when learning new skills, people tend to first simplify coordination by 'freezing' their degrees of freedom, after which they start building efficiency by 'releasing' specific degrees of freedom. If a similar pattern of development can be established post-stroke, it would imply that lessons learned in sports skill acquisition can also be implemented to optimize stroke rehabilitation. The current scoping review aims to assess whether the Bernsteinian freezing-to-releasing stages of learning also apply to developing whole-body movement skills after stroke. To this end, we systematically screened the existing literature for studies involving a longitudinal measure of whole-body coordination after a stroke. Only five articles met the criteria for inclusion, indicating a gap in research on this topic. Based on the observations within these articles, we could neither confirm nor reject whether the freezing-to-releasing process can apply after a stroke. We could, however, hypothesize a detailed description of the freezing-to-releasing process, which can be assessed in future works.

Teachers' Perceptions of Applying Contemporary Skill Acquisition Approaches in High School Physical Education

Using contemporary skill acquisition approaches to skill learning appears to be a worthwhile pedagogical option for teachers and coaches in sports and Physical Education (PE). However, PE at the High School level in New Zealand has assessment components that are still underpinned by traditional and outdated skill learning theories. In response to this challenge, two motivated Heads of Department in PE undertook a department-wide professional development initiative to teach the national standard assessment via the use of a contemporary skill acquisition approach, which is student-centred, with an emphasis on enhancing exploratory learning and encouraging autonomy. Each department worked together over a 10-week period with a Higher Education specialist in skill acquisition to design and teach using contemporary skill acquisition approaches. Qualitative data was collected via semi-structured focus group interviews. Insightful data on the influence of teaching using contemporary skill acquisition approaches was acquired from the teachers in the two PE departments. It was found that substantial pedagogical practice changes were achieved by the teachers (e.g., less focus on ideal technique and more on varying the context). They also enjoyed the learning experience that the contemporary skill acquisition approach offered as compared to their previous experience of more traditional teaching approaches, which have a focus on knowledge acquirement with little opportunities for exploratory learning. In addition, from a practical perspective, teachers were observed to demonstrate greater engagement in professional conversations around learning and could see greater relevance in the transfer of learning in the use of contemporary skill acquisition approaches to other teaching contexts.

Differences in Motor Control Strategies of Jumping Tasks, as Revealed by Group and Individual Analysis

The aim of this study was to investigate the motor control strategies adopted when performing two jumping tasks with different task demands when analysed at an individual and group level. Twenty-two healthy individuals performed two jumping tasks: jumping without the use of an arm swing (CMJnas) and jumping starting in a plantar flexed position with the use of an arm swing (PF). Principal component analysis (PCA) was performed using hip, knee and ankle joint moment data on individual (PCAi) and group data (PCAc). The results demonstrate that a greater number of PCs are required to explain the majority of variance within the dataset in the PF condition at both an individual and group level, compared to CMJnas condition. Although common control strategies were observed between the two jumping conditions, differences in the organisation of the movement (PC loading coefficients) were observed. Results from the group analysis did not completely reflect the individual strategies used to perform each jumping task and highlight the value in performing individual analysis to determine emergent control strategies.

Movement form of the overarm throw for children at 6, 10 and 14 years of age

This study investigated overarm throwing technique at different developmental ages in children from the perspective of three distinct, though potentially complementary, approaches to motor skill acquisition. Children at 6, 10, and 14 years of age (N = 18), completed dominant overarm throws during which whole-body kinematic data were collected. Firstly, application of Newell's ([1985]. Coordination, control and skill. In Advances in Psychology (Vol. 27, pp. 295-317). North-Holland.) stages of learning identified three distinct age-related coupling modes between forward motion of the centre-of-mass (CoM) and the wrist, which demonstrated a greater range of couplings for older children. Secondly, in line with Bernstein's ([1967]. The coordination and regulation of movement. London: Pergamon Press.) hypothesis of freezing before freeing degrees of freedom, a significantly smaller range of motion (ROM) at the ankle and knee joints, but greater ROM at the hip and upper limb joints was found for the 6 year old group compared to the 10 and 14 year old groups. Thirdly, based on the components model (Roberton & Halverson [1984]. Developing children-their changing movement: A guide for teachers. Lea & Febiger.), the overarm throws demonstrated by 6 year olds were characterised as primitive to intermediate, where 10 and 14 year old's throws were characterised by the penultimate action level for each component. Characteristics of CoM-wrist coupling more clearly identify children's age-related technique and highlight the importance of posture-ball release dynamics. The posture-ball dynamics were supported by changes in ROM and the components model, revealing the complementary nature of the three approaches to the analysis of age-related differences in overarm throwing action.

Task Demand Changes Motor Control Strategies in Vertical Jumping

The purpose of this study was to examine the motor control strategies employed to control the degrees of freedom when performing a lower limb task with constraints applied at the hip, knee, and ankle. Thirty-five individuals performed vertical jumping tasks: hip flexed, no knee bend, and plantar flexed. Joint moment data from the hip, knee, and ankle were analyzed using principal component analysis (PCA). In all PCA performed, a minimum of two and maximum of six principal components (PC) were required to describe the movements. Similar reductions in dimensionality were observed in the hip flexed and no knee bend conditions (3PCs), compared to the plantar flexed condition (5PCs). A proximal to distal reduction in variability was observed for the hip flexed and no knee bend conditions but not for the plantar flexed condition. Collectively, the results suggest a reduction in the dimensionality of the movement occurs despite the constraints imposed within each condition and would suggest that dimensionality reduction and motor control strategies are a function of the task demands.

Freezing Degrees of Freedom During Motor Learning: A Systematic Review

According to Bernstein, the central nervous system solution to the human body’s enormous variation in movement choice and control when directing movement—the problem of degrees of freedom (DF)—is to freeze the number of possibilities at the beginning of motor learning. However, different strategies of freezing DF are observed in literature, and the means of selection of the control strategy during learning is not totally clear. This review investigated the possible effects of the class and objectives of the skill practiced on DF control strategies. The results of this review suggest that freezing or releasing the DF at the beginning of learning does not depend on the class (e.g., discrete skill class: football kick, dart throwing; continuous skill class: athletic march, handwriting) or objective of the skill (e.g., balance, velocity, and accuracy), in isolation. However, an interaction between these two skill elements seems to exist and influences the selection of the DF control strategy.

A mobility-based classification of closed kinematic chains in biomechanics and implications for motor control

Closed kinematic chains (CKCs), links connected to form one or more closed loops, are used as simple models of musculoskeletal systems (e.g. the four-bar linkage). Previous applications of CKCs have primarily focused on biomechanical systems with rigid links and permanently closed chains, which results in constant mobility (the total degrees of freedom of a system). However, systems with non-rigid elements (e.g. ligaments and muscles) and that alternate between open and closed chains (e.g. standing on one foot versus two) can also be treated as CKCs with changing mobility. Given that, in general, systems that have fewer degrees of freedom are easier to control, what implications might such dynamic changes in mobility have for motor control? Here, I propose a CKC classification to explain the different ways in which mobility of musculoskeletal systems can change dynamically during behavior. This classification is based on the mobility formula, taking into account the number of loops in the CKC and the nature of the constituent joint mobilities. I apply this mobility-based classification to five biomechanical systems: the human lower limbs, the operculum-lower jaw mechanism of fishes, the upper beak rotation mechanism of birds, antagonistic muscles at the human ankle joint and the human jaw processing a food item. I discuss the implications of this classification, including that mobility itself may be dynamically manipulated to simplify motor control. The principal aim of this Commentary is to provide a framework for quantifying mobility across diverse musculoskeletal systems to evaluate its potentially key role in motor control.

Integrated Analysis of Young Swimmers' Sprint Performance

To analyze young swimmers' performance regarding sex and skill level, 23 boys and 26 girls (15.7 ± 0.8 and 14.5 ± 0.8 years old, respectively) were assessed for anthropometry, flexibility, strength, drag, coordination, and biomechanical variables. During a 50-m maximal front-crawl bout, seven aerial and six underwater Qualisys cameras assessed kinematics, and a load cell was used to measure drag (Tedea, United Kingdom) and tethered swimming force. A multivariate analysis of variance test (p < .05) enabled us to observe differences between skill levels in speed, stroke frequency, stroke index, and intracyclic velocity variations, but most relevant differences were noticed when comparing sexes, particularly for anthropometrics, shoulder flexibility, speed, stroke frequency, stroke length, drag, mechanical power, power per stroke, and maximal and mean force. Considering the included variables, only male swimmers' performance could be predicted through multiple linear regression, with stroke index, left shoulder flexion, and intracycle velocity variations showing great importance in achieving better results.

Task experience influences coordinative structures and performance variables in learning a slalom ski-simulator task

The experiment investigated the progressions of the qualitative and quantitative changes in the movement dynamics of learning the ski-simulator as a function of prior-related task experience. The focus was the differential timescales of change in the candidate collective variable, neuromuscular synergies, joint motions, and task outcome as a function of learning over 7 days of practice. Half of the novice participants revealed in day 1 a transition of in-phase to anti-phase coupling of center of mass (CoM)-platform motion whereas the remaining novices and experienced group all produced on the first trial an anti-phase CoM-platform coupling. The experienced group also had initially greater amplitude and velocity of platform motion-a performance advantage over the novice group that was reduced but not eliminated with 7 days of practice. The novice participants who had an in-phase CoM-platform coupling on the initial trials of day 1 also showed the most restricted platform motion in those trials. Prior-related practice experience differentially influenced the learning of the task as evidenced by both the qualitative organization and the quantitative motion properties of the individual degrees of freedom (dof) to meet the task demands. The findings provide further evidence to the proposition that CoM-platform coupling is a candidate collective variable in the ski-simulator task that provides organization and boundary conditions to the motions of the individual joint dof and their couplings.

Understanding constraints on sport performance from the complexity sciences paradigm: An ecological dynamics framework

Glazier's suggestion for the constraints-led approach as a GUT for sport performance is a worthy proposal. What is missing from these preliminary insights is a principled basis, in the form of pillars, for understanding the cornerstones of the sports medicine profession, and this lack of an overarching theoretical framework is also somewhat of a limitation in Glazier's initial ideas, as we argue later. Here we suggest that his preliminary proposal would benefit from considering a more comprehensive ontological positioning within the complexity sciences paradigm to benefit from conceptualising athletes and sports teams as complex adaptive systems. We argue that ecological dynamics provides a more encompassing rationale than the constraint-led approach because it is a multi-dimensional theoretical framework shaped by many relevant disciplines.

Changes in movement organization and control strategies when learning a biomechanically constrained gait pattern, racewalking: a PCA study

Combining advances from gait analysis and motor learning fields, this study aims to examine invariant characteristics and practice-related changes in the control of walking gait when learning a biomechanically constrained pattern, racewalking (RW). RW’s regulation imposes a straightened knee at the stance phase which differentiates it qualitatively from normal walking. Using 3D motion analysis, we computed key kinematic variables from a whole-body model. Principal component analysis was then used as a tool to evaluate the evolution of normal walking synergies (S0) immediately at the first practice session (S1) and further with practice (S1–S4). Before the start of practice, normal walking was characterized by two predominant control dimensions explaining an upper-extremities/antero-posterior component (PC1) and a lower-extremities/vertical component (PC2). Compared to normal walking, the immediate increase at S1 in the number of PCs needed to explain a significant portion of movement variance could be suggestive of a recruitment of a task-specific component. With practice, the significant decrease in the variance accounted for by PC1 and in the correlations between many variables could indicate a destabilization of spontaneous tendencies to facilitate the adoption of more task-specific coordinative pattern. PC2 seemed to be reinforced with practice where a significant increase in its explained variance was observed. In sum, this study shows that common features in the gait control are preserved with practice, and the movement reorganization, however, seems rather defined by shifts in the relative contribution of some variables within each PC.

Biomechanical metrics of aesthetic perception in dance

The brain may be tuned to evaluate aesthetic perception through perceptual chunking when we observe the grace of the dancer. We modelled biomechanical metrics to explain biological determinants of aesthetic perception in dance. Eighteen expert (EXP) and intermediate (INT) dancers performed développé arabesque in three conditions: (1) slow tempo, (2) slow tempo with relevé, and (3) fast tempo. To compare biomechanical metrics of kinematic data, we calculated intra-excursion variability, principal component analysis (PCA), and dimensionless jerk for the gesture limb. Observers, all trained dancers, viewed motion capture stick figures of the trials and ranked each for aesthetic (1) proficiency and (2) movement smoothness. Statistical analyses included group by condition repeated-measures ANOVA for metric data; Mann-Whitney U rank and Friedman's rank tests for nonparametric rank data; Spearman's rho correlations to compare aesthetic rankings and metrics; and linear regression to examine which metric best quantified observers' aesthetic rankings, p < 0.05. The goodness of fit of the proposed models was determined using Akaike information criteria. Aesthetic proficiency and smoothness rankings of the dance movements revealed differences between groups and condition, p < 0.0001. EXP dancers were rated more aesthetically proficient than INT dancers. The slow and fast conditions were judged more aesthetically proficient than slow with relevé (p < 0.0001). Of the metrics, PCA best captured the differences due to group and condition. PCA also provided the most parsimonious model to explain aesthetic proficiency and smoothness rankings. By permitting organization of large data sets into simpler groupings, PCA may mirror the phenomenon of chunking in which the brain combines sensory motor elements into integrated units of behaviour. In this representation, the chunk of information which is remembered, and to which the observer reacts, is the elemental mode shape of the motion rather than physical displacements. This suggests that reduction in redundant information to a simplistic dimensionality is related to the experienced observer's aesthetic perception.

Postural sway and gaze can track the complex motion of a visual target

Variability is an inherent and important feature of human movement. This variability has form exhibiting a chaotic structure. Visual feedback training using regular predictive visual target motions does not take into account this essential characteristic of the human movement, and may result in task specific learning and loss of visuo-motor adaptability. In this study, we asked how well healthy young adults can track visual target cues of varying degree of complexity during whole-body swaying in the Anterior-Posterior (AP) and Medio-Lateral (ML) direction. Participants were asked to track three visual target motions: a complex (Lorenz attractor), a noise (brown) and a periodic (sine) moving target while receiving online visual feedback about their performance. Postural sway, gaze and target motion were synchronously recorded and the degree of force-target and gaze-target coupling was quantified using spectral coherence and Cross-Approximate entropy. Analysis revealed that both force-target and gaze-target coupling was sensitive to the complexity of the visual stimuli motions. Postural sway showed a higher degree of coherence with the Lorenz attractor than the brown noise or sinusoidal stimulus motion. Similarly, gaze was more synchronous with the Lorenz attractor than the brown noise and sinusoidal stimulus motion. These results were similar regardless of whether tracking was performed in the AP or ML direction. Based on the theoretical model of optimal movement variability tracking of a complex signal may provide a better stimulus to improve visuo-motor adaptation and learning in postural control.

Neurobiological degeneracy: supporting stability, flexibility and pluripotentiality in complex motor skill

This paper investigated neurobiological degeneracy of the motor system that emerged as a function of levels of environmental constraint. Fourteen participants performed a breaststroke-swimming task that required them to develop a specific biomechanically expert pattern and in turn provide the basis for a suitable task vehicle to study the functional role of movement variability. Inter-limb coordination was defined based on the computation of continuous relative phase between elbow and knee oscillators. Unsupervised cluster analysis on arm-leg coordination revealed the existence of different patterns of coordination when participants achieved the same task goal under different levels of environmental constraints (i.e. different amounts of forward resistances). In addition, clusters differed in terms of higher order derivatives (e.g., joint angular velocity, joint amplitude), suggesting an effective role for degeneracy in learning by allowing the exploration of the key relationships between motor organization and interacting constraints. There is evidence to suggest that neurobiological degeneracy supports the potential for motor re-organization to enhance motor learning.

Cognitive load results in motor overflow in essential tremor

SK is an 84-year-old woman diagnosed with essential tremor (ET) but no cognitive deficits. In this experiment, we tested the effects of mental rotation (a form of additional cognitive load) during reaching behavior (with the right hand) on the tremor profile of the non-moving left hand. We observed a marked increase in tremor and its variability, as well as the "freezing" of the movement pattern as effects of the cognitive load. These findings imply cognitive-motor overlaps in patients with ET, raising the possibility that the deficits reflect the loss of a common pool of neural resources, despite the heterogeneity of the symptoms of the disorder.

Changes in kicking pattern: effect of experience, speed, accuracy, and effective striking mass

PURPOSE

The purposes of this study were to: (a) examine the effect of experience and goal constraints (speed, accuracy) on kicking patterns; (b) determine if effective striking mass was independent of ankle velocity at impact; and (c) determine the accuracy of kicks relative to independent factors.

METHOD

Twenty participants were recruited to kick at 3 different velocities with and without an accuracy requirement. Multivariate analysis of variance determined if relative timing of joint angular velocities changed during the kick. Chi-square analysis determined if calculated effective mass was independent of ankle velocity at impact. Analysis of variance (ANOVA) was used to examine differences in absolute constant error and variable error according to independent factors.

RESULTS

Results indicated that experience and speed affect absolute timing of joint velocities with no changes in the relative timing of peak joint velocity across independent factors. Chi-square analysis indicated that calculated effective mass is not independent of ankle velocity. ANOVA indicated that experienced performers displayed less variability error than did inexperienced performers.

CONCLUSION

It was concluded that: (a) Experience, velocity, and accuracy do not affect the relative timing of kicks; (b) kickers trade ankle velocity at impact for greater effective striking mass and ball velocity; and (c) variability in ball placement is affected by experience.

Postural coordination patterns as a function of rhythmical dynamics of the surface of support

This study investigated the organization of postural coordination patterns as a function of the rhythmical dynamics of the surface of support. We examined how the number and nature of the dynamical degrees of freedom in the movement coordination patterns changed as a function of the amplitude and frequency of support surface motion. Young adult subjects stood on a moving platform that was translated sinusoidally in anterior-posterior (AP) direction with the task goal to maintain upright bipedal postural balance. A force platform measured the kinetics at the surface of support and a 3D motion analysis system recorded torso and joint kinematics. Principal components analysis (PCA) identified four components overall, but increasing the average velocity of the support surface reduced the modal number of components of the postural coordination pattern from three to two. The analysis of joint motion loadings on the components revealed that organizational properties of the postural pattern also changed as a function of platform dynamics. PC1 (61.6-73.2 %) was accounted for by ankle, knee, and hip motion at the lowest velocity conditions, but as the velocity increased, ankle and hip variance dominated. In PC2 (24.2-20.2 %), the contribution of knee motion significantly increased while that of ankle motion decreased. In PC3 (9.7-5.1 %) neck motion contributed significantly at the highest velocity condition. Collectively, the findings show that the amplitude and frequency of the motion of the surface of support maps redundantly though preferentially to a small set of postural coordination patterns. The higher platform average velocities led to a reduction in the number of dynamical degrees of freedom of the coordination mode and different weightings of joint motion contributions to each component.

Learning a stick-balancing task involves task-specific coupling between posture and hand displacements

Theories of motor learning argue that the acquisition of novel motor skills requires a task-specific organization of sensory and motor subsystems. We examined task-specific coupling between motor subsystems as subjects learned a novel stick-balancing task. We focused on learning-induced changes in finger movements and body sway and investigated the effect of practice on their coupling. Eight subjects practiced balancing a cylindrical wooden stick for 30 min a day during a 20 day learning period. Finger movements and center of pressure trajectories were recorded in every fifth practice session (4 in total) using a ten camera VICON motion capture system interfaced with two force platforms. Motor learning was quantified using average balancing trial lengths, which increased with practice and confirmed that subjects learned the task. Nonlinear time series and phase space reconstruction methods were subsequently used to investigate changes in the spatiotemporal properties of finger movements, body sway and their progressive coupling. Systematic increases in subsystem coupling were observed despite reduced autocorrelation and differences in the temporal properties of center of pressure and finger trajectories. The average duration of these coupled trajectories increased systematically across the learning period. In short, the abrupt transition between coupled and decoupled subsystem dynamics suggested that stick balancing is regulated by a hierarchical control mechanism that switches from collective to independent control of the finger and center of pressure. In addition to traditional measures of motor performance, dynamical analyses revealed changes in motor subsystem organization that occurred when subjects learned a novel stick-balancing task.

Distinct consolidation outcomes in a visuomotor adaptation task: Off-line leaning and persistent after-effect

Consolidation is a time-dependent process responsible for the storage of information in long-term memory. As such, it plays a crucial role in motor learning. In two experiments, we sought to determine whether one's performance influences the outcome of the consolidation process. We used a visuomotor adaptation task in which the cursor moved by the participants was rotated 30 degrees clockwise. Thus, participants had to learn a new internal model to compensate for the rotation of the visual feedback. The results indicated that when participants showed good adaptation in the first session, consolidation resulted in a persistent after-effect in a no-rotation transfer test; they had difficulty returning to their normal no-rotation internal model. However, when participants showed poor adaptation in the first session, consolidation led to significant off-line learning (between sessions improvement) but labile after-effects. These observations suggest that distinct consolidation outcomes (off-line learning and persistent after-effect) may occur depending on the learner's initial performance.

Visuo-postural adaptation during the acquisition of a visually guided weight-shifting task: age-related differences in global and local dynamics

The effects of aging on the acquisition of a novel visuo-postural coordination task were addressed at two levels: (a) changes in the intersegmental coordination (local dynamics) (b) changes in the coupling of postural sway to the visual driving stimulus (global dynamics). Twelve elderly (age: 71.2 +/- 6.4 years; height: 169.3 +/- 3.8 cm; mass: 72.4 +/- 6.1 kg) and 12 young women (age: 27.1 +/- 4.9 years; height: 178.3 +/- 2.9 cm; mass: 56.7 +/- 4.1 kg) practiced a visually guided Weight-Shifting (WS) task while standing on a dual force platform. The participants were asked to keep the vertical force applied by each limb within a +/-30% force boundary that was visually specified by a target sine-wave signal. Practice consisted of three blocks of five trials performed in 1-day, followed by a block of five trials performed 24 h later. Ground reaction forces and segment (shank, pelvis, and upper trunk) angular kinematics were synchronously sampled through an A/D acquisition board and further analyzed employing spectral and coherence analysis. Elderly women had longer WS cycles, lower response gain, and higher within-trial variability, suggesting a weaker coupling between the visual stimulus and the response force. Spectral analysis of the ground reaction forces confirmed that regardless of age, visuo-postural coupling improved with practice. However, the recruitment of local degrees of freedom was different between the two age groups. With practice, young performers increased peak coherence between the pelvis and the upper trunk and reduced peak power of segment oscillations in the pitch direction. On the other hand, elderly women decreased active upper trunk rotation while shifting control to the lower limb. It is suggested that different functional coordination solutions are possible for attaining the same overall task goal. These solutions are determined by age-related constraints in the physiological systems supporting postural control.