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Freezing Degrees of Freedom During Motor Learning: A Systematic Review

Anderson Nascimento Guimarães, Herbert Ugrinowitsch, Juliana Bayeux Dascal, Alessandra Beggiato Porto, and Victor Hugo Alves Okazaki

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.

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New Insight on Motor Behavior: The Link Between the Hopping Task and the Tracing Performance as Hint of Gross and Fine Motor Functions

Danilo Bondi, Sergio Di Sano, Vittore Verratti, Giampiero Neri, Tiziana Aureli, and Tiziana Pietrangelo

The gross motor coordination tasks are thought to be likely not linked to the fine motor coordination tasks. The authors aimed to investigate this matter through a network analysis linking graphomotor (by tablet PC tracing), gross coordination (by Körperkoordinationstest für Kinder items), and strength (by handgrip) parameters in school children. Interestingly, the authors found that “Hopping” was the strongest central node, with linkages to “Quality” and “Speed” on tracing test. Handgrip strength did not link to gross coordination and graphomotor parameters, except with “Pressure.” Graphomotor performances suggested substantial peculiarities in developmental trajectories. Sport participation did not influence gross coordination nor graphomotor performances. The authors suggest considering the functional link between hopping and graphomotricity both in planning physical education and in understanding coordination impairments, through the developmental trajectories.

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Effect of Different Evasion Maneuvers on Anticipation and Visual Behavior in Elite Rugby League Players

Jonathan D. Connor, Robert G. Crowther, and Wade H. Sinclair

This study examined the anticipation and visual behavior of elite rugby league players during two different evasion maneuvers (side- and split-steps). Participants (N = 48) included elite rugby league players (n = 38) and controls (n = 10). Each participant watched videos consisting of side- and split-steps, and anticipation of movement and eye behavior were measured. No significant differences between the groups or evasion maneuvers were found. The split-step was significantly harder to predict. Elite players appeared to spend more time viewing the torso and mid-region of the body compared with the controls.

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Inter- and Intrasubject Similarity of Muscle Synergies During Bench Press With Slow and Fast Velocity

Afshin Samani and Mathias Kristiansen

We investigated the effect of low and high bar velocity on inter- and intrasubject similarity of muscle synergies during bench press. A total of 13 trained male subjects underwent two exercise conditions: a slow- and a fast-velocity bench press. Surface electromyography was recorded from 13 muscles, and muscle synergies were extracted using a nonnegative matrix factorization algorithm. The intrasubject similarity across conditions and intersubject similarity within conditions were computed for muscle synergy vectors and activation coefficients. Two muscle synergies were sufficient to describe the dataset variability. For the second synergy activation coefficient, the intersubject similarity within the fast-velocity condition was greater than the intrasubject similarity of the activation coefficient across the conditions. An opposite pattern was observed for the first muscle synergy vector. We concluded that the activation coefficients are robust within conditions, indicating a robust temporal pattern of muscular activity across individuals, but the muscle synergy vector seemed to be individually assigned.

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Volume 22 (2018): Issue 1 (Jan 2018)

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Precision-Dependent Changes in Motor Variability During Sustained Bimanual Reaching

Alessia Longo and Ruud Meulenbroek

Movement variability of the upper limb was investigated using a bimanual Fitts’ task. Participants tapped rhythmically between target-pairs of different index of difficulties for three intervals of 20 min each. We studied the effects of index of difficulties and time-on-task on movement time, end-point variability, approximate entropy, and standard deviation of the relative phase. Lower index of difficulties and time-on-task caused decreasing movement time and increasing end-point variability. Moreover, standard deviation of the relative phase and approximate entropy moderately increased. By looking into the long-term effects of a sustained bimanual Fitts’ task, this is the first time such movement variability increase is demonstrated in multiple variability indices. The relevance of the findings for future studies on work-related musculoskeletal disorders is being discussed.

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Should Ballet Dancers Vary Postures and Underfoot Surfaces When Practicing Postural Balance?

Nili Steinberg, Gordon Waddington, Roger Adams, Janet Karin, and Oren Tirosh

Background: Postural balance (PB) is an important component skill for professional dancers. However, the effects of different types of postures and different underfoot surfaces on PB have not adequately been addressed. Purpose: The main aim of this study was to investigate the effect of different conditions of footwear, surfaces, and standing positions on static and dynamic PB ability of young ballet dancers. Methods: A total of 36 male and female young professional ballet dancers (aged 14–19 years) completed static and dynamic balance testing, measured by head and lumbar accelerometers, while standing on one leg in the turnout position, under six different conditions: (1) “relaxed” posture; (2) “ballet” posture; (3) barefoot; (4) ballet shoes with textured insoles; (5) barefoot on a textured mat; and (6) barefoot on a spiky mat. Results: A condition effect was found for static and dynamic PB. Static PB was reduced when dancers stood in the ballet posture compared with standing in the relaxed posture and when standing on a textured mat and on a spiky mat (p < .05), and static PB in the relaxed posture was significantly better than PB in all the other five conditions tested. Dynamic PB was significantly better while standing in ballet shoes with textured insoles and when standing on a spiky mat compared with all other conditions (p < .05). Conclusions: The practical implications derived from this study are that both male and female dancers should try to be relaxed in their postural muscles when practicing a ballet aligned position, including dance practice on different types of floors and on different types of textured/spiky materials may result in skill transfer to practice on normal floor surfaces, and both static and dynamic PB exercises should be assessed and generalized into practical dance routines.

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Somatosensory Electrical Stimulation Does Not Augment Motor Skill Acquisition and Intermanual Transfer in Healthy Young Adults—A Pilot Study

János Négyesi, Menno P. Veldman, Kelly M.M. Berghuis, Marie Javet, József Tihanyi, and Tibor Hortobágyi

Sensory input can modify motor function and magnify interlimb transfer. We examined the effects of low-intensity somatosensory electrical stimulation (SES) on motor practice-induced skill acquisition and intermanual transfer. Participants practiced a visuomotor skill for 25 min and received SES to the practice or the transfer arm. Responses to single- and double-pulse transcranial magnetic stimulation were measured in both extensor carpi radialis. SES did not further increase skill acquisition (motor practice with right hand [RMP]: 30.8% and motor practice with right hand + somatosensory electrical stimulation to the right arm [RMP + RSES]: 27.8%) and intermanual transfer (RMP: 13.6% and RMP + RSES: 9.8%) when delivered to the left arm (motor practice with right hand + somatosensory electrical stimulation to the left arm [RMP + LSES]: 44.8% and 18.6%, respectively). Furthermore, transcranial magnetic stimulation measures revealed no changes in either hand. Future studies should systematically manipulate SES parameters to better understand the mechanisms of how SES affords motor learning benefits documented but not studied in patients.

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Systematic, Unintended Drifts in the Cyclic Force Produced with the Fingertips

Satyajit Ambike, Daniela Mattos, Vladimir Zatsiorsky, and Mark Latash

Cyclic isometric finger-force patterns established using visual feedback show systematic drifts when the feedback is removed. Force changes at multiple time scales and in opposite directions have been reported. For further characterization of these drifts, healthy subjects produced isometric, cyclic finger force with and without visual feedback at various initial amplitudes and frequencies. We hypothesized that on feedback removal, the amplitude will be attracted toward a preferred value that is frequency dependent. We found that the amplitude always increased after feedback removal. The magnitude of the amplitude increase changed with initial frequency, but it was invariant over the explored range of initial amplitudes. Thus, the existence of a preferred amplitude of force oscillations was not supported. We interpret these results within the referent configuration and the referent configuration back-coupling hypotheses. These data will inform a mathematical model of finger-force drifts. However, currently, they raise more questions than they answer, and a coherent account of finger-force drifts remains a challenge.

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Unstable Footwear Affects Magnitude and Structure of Variability in Postural Control

Michael Buchecker, Stefan Wegenkittl, Thomas Stöggl, and Erich Müller

This study evaluated the amount, and particularly, the structure of variability in postural control accompanying an unstable shoe (US) application. Mediolateral and anterior–posterior center of pressure signals plus electromyographic profiles of the tibialis anterior and gastrocnemius medialis were recorded in 29 asymptomatic men while wearing both US and flat shoes. Statistical analysis included common measures of dispersion as well as sample entropy and largest Lyapunov exponent estimates. Data were compared by two-way repeated-measures analysis of variance. Corresponding main effects of footwear revealed that, in contrast to the flat shoes condition, the US intervention consistently increased center of pressure and electromyographic net fluctuations and rendered the overall system less complex, as reflected by the lower sample entropy and higher Lyapunov exponent values observed throughout. Accordingly, employing US in stance should be functional concerning motor development; however, the greater sensitivity of US users to external perturbations must not be overlooked and warrants further investigation.