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Altered Spatiotemporal Gaze Dynamics During Unexpected Obstacle Negotiation in a Fatigued State

Jacob W. Hinkel-Lipsker, Nicole M. Stoehr, Pranavi L. Depur, Michael A. Weise, Joshua A. Vicente, Stefanie A. Drew, and Sean M. Rogers

Humans use their peripheral vision during locomotion to perceive an approaching obstacle in their path, while also focusing central gaze on steps ahead of them. However, certain physiological and psychological factors may change this strategy, such as when a walker is physically fatigued. In this study, 21 healthy participants walked through a dark room while wearing eye tracking glasses before and following intense exercise. Obstacles were placed in random locations along their path and became illuminated when participants approached them. Results indicate that, when fatigued, participants had altered spatial gaze strategies, including more frequent use of central gaze to perceive obstacles and an increased gaze angular displacement. However, there were no changes in temporal gaze strategies following exercise. These findings reveal how physical fatigue alters one’s visual perception of their environment during locomotion, and may partially explain why people are at greater risk of trips and falls while fatigued.

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Are Men and Women Equally Affected by Load Carriage While Landing? Analysis of Balance in Spanish Infantry Soldiers

Eva Orantes-Gonzalez and J. Heredia-Jimenez

In this study, the effect of carrying combat equipment and a backpack on balance between men and women was analyzed by simulating a jump out of an armored fighting vehicle, together with the influence of body composition variables. Thirty-seven men and eight women participated in this study. Three landings were performed by simulating a jump from a wheeled armored vehicle carrying no load, carrying the combat equipment and backpack condition. A force plate was used to measure the amplitude and velocity displacement of the center of pressure and the stabilization time. A significant load effect was found on the total velocity and medial–lateral velocity. The weight of the combat equipment and the body composition variables did not correlate with the balance variables. Male and female soldiers showed similar body balance while carrying military combat equipment.

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Role of Post-Trial Visual Feedback on Unintentional Force Drift During Isometric Finger Force Production Tasks

S. Balamurugan, Rachaveti Dhanush, and S.K.M. Varadhan

A reduction in fingertip forces during a visually occluded isometric task is called unintentional drift. In this study, unintentional drift was studied for two conditions, with and without “epilogue.” We define epilogue as the posttrial visual feedback in which the outcome of the just-concluded trial is shown before the start of the next trial. For this study, 14 healthy participants were recruited and were instructed to produce fingertip forces to match a target line at 15% maximum voluntary contraction. The results showed a significant reduction in unintentional drift in the epilogue condition. This reduction is probably due to the difference in the shift in λ, the threshold of the tonic stretch reflex, the hypothetical control variable that the central controller can set.

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The Role of Predictability of Perturbation in Control of Posture: A Scoping Review

Tippawan Kaewmanee and Alexander S. Aruin

Efficient maintenance of posture depends on the ability of humans to predict consequences of a perturbation applied to their body. The purpose of this scoping review was to map the literature on the role of predictability of a body perturbation in control of posture. A comprehensive search of MEDLINE, EMBASE, and CINAHL databases was conducted. Inclusion criteria were studies of adults participating in experiments involving body perturbations, reported outcomes of posture and balance control, and studies published in English. Sixty-three studies were selected. The reviewed information resources included the availability of sensory information and the exposure to perturbations in different sequences of perturbation magnitudes or directions. This review revealed that people use explicit and implicit information resources for the prediction of perturbations. Explicit information consists of sensory information related to perturbation properties and timing, whereas implicit information involves learning from repetitive exposures to perturbations of the same properties.

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Torso Kinematics in Human Rolling Do Not Change When Upper Extremity Motion Is Constrained

Linh Q. Vu, Rahul Agrawal, Mahdi Hassan, and Nils A. Hakansson

Human rolling, as turning in bed, is a fundamental activity of daily living. A quantitative analysis of rolling could help identify the neuromusculoskeletal disorders that prohibit rolling and develop interventions for individuals who cannot roll. This study sought to determine whether crossing the arms over the chest would alter fundamental coordination patterns when rolling. Kinematic data were collected from 24 subjects as they rolled with and without their arms crossed over their chest. Crossing the arms decreased the mean peak angular velocities of the shoulders (p = .001) and pelvis (p = .013) and influenced the mean duration of the roll (p = .057). There were no fundamental differences in shoulder and pelvis coordination when rolling with the arms crossed over the chest, implying that the arms may not have a major role in rolling.

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The Imitation Game in Children With Tourette Syndrome: A Lack of Impulse Control to Mirror Environmental Stimuli

Matteo Briguglio, Roberta Galentino, Sara De Michele, Bernardo Dell’Osso, Leonardo Fogassi, and Mauro Porta

The learning process in humans requires continuous contacts with environmental stimuli, especially during neurodevelopmental growth. These functions are assisted by the coding potential of mirror neurons to serve social interactions. This ability to learn imitating the observed behavior is no longer necessary during adulthood, and control mechanisms prevent automatic mirroring. However, children with Gilles de la Tourette syndrome could encounter coding errors at the level of the mirror neurons system as these cortical regions are themselves the ones affected in the syndrome. Combined with impulsivity, the resulting sign would be a manifest echopraxia that persists throughout adulthood, averting these individuals from the appraisal of a spot-on motor control.

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Increased Speed Elicited More Automatized but Less Predictable Control in Cyclical Arm and Leg Movements

Werner A.F. van de Ven, Jurjen Bosga, Wim Hullegie, Wiebe C. Verra, and Ruud G.J. Meulenbroek

The present study explores variations in the degree of automaticity and predictability of cyclical arm and leg movements. Twenty healthy adults were asked to walk on a treadmill at a lower-than-preferred speed, their preferred speed, and at a higher-than-preferred speed. In a separate, repetitive punching task, the three walking frequencies were used to cue the target pace of the cyclical arm movements. Movements of the arms, legs, and trunk were digitized with inertial sensors. Whereas absolute slope values (|β|) of the linear fit to the power spectrum of the digitized movements (p < .001, η2 = .676) were systematically smaller in treadmill walking than in repetitive punching, sample entropy measures (p < .001, η2 = .570) were larger reflecting the former task being more automated but also less predictable than the latter task. In both tasks, increased speeds enhanced automatized control (p < .001, η2 = .475) but reduced movement predictability (p = .008, η2 = .225). The latter findings are potentially relevant when evaluating effects of task demand changes in clinical contexts.

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Volume 25 (2021): Issue 4 (Oct 2021)

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Expertise- and Tempo-Related Performance Differences in Unimanual Drumming

Bryony Buck, Scott Beveridge, Gerard Breaden Madden, and Hans-Christian Jabusch

Background: High-speed drumming requires precise control over the timing, velocity, and magnitude of striking movements. Aim: To examine effects of tempo and expertise on unaccented repetitive drumming performance using 3D motion capture. Methods: Expert and amateur drummers performed unimanual, unaccented, repetitive drum strikes, using their dominant right hand, at five different tempi. Performance was examined with regard to timing variability, striking velocity variability, the ability to match the prescribed tempo, and additional variables. Results: Permutated multivariate analysis of variance (PERMANOVA) revealed significant main effects of tempo (p < .001) and expertise (p <.001) on timing variability and striking velocity variability; low timing variability and low striking velocity variability were associated with low/medium tempo as well as with increased expertise. Individually, improved precision appeared across an optimum tempo range. Precision was poorest at maximum tempo (400 hits per minute) for precision variables. Conclusions: Expert drummers demonstrated greater precision and consistency than amateurs. Findings indicate an optimum tempo range that extends with increased expertise.

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Effects of Eight Methods and Five Steps of Tai Chi Practice on Balance Control Among Older Adults

Xiu Hu, Shaojun Lyu, Min Mao, Jianwei Zhang, Wei Sun, Cui Zhang, and Qipeng Song

The team developed the newly compiled eight methods and five steps of Tai Chi (EMFSTC), which includes introductory routines to Tai Chi characterized by simple structures. This study examined the effectiveness of EMFSTC practice on balance control. A total of 31 participants were randomly assigned to EMFSTC (n = 15, age = 66.4 ± 1.7 years, received 16-week EMFSTC practice) or control (n = 16, age = 66.7 ± 1.8 years, received no practice) groups. Significant group by training interactions were observed. After EMFSTC practice, balance control improved, as indicated by decreased root mean square and mean velocity of center of pressure, proprioception threshold during knee extension, and plantar tactile sensitivity threshold at the arch. EMFSCT can be an effective rehabilitation modality to improve balance control among older adults.