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Etem Curuk, Yunju Lee and Alexander S. Aruin

While maintaining vertical posture, the central nervous system (CNS) uses two main types of adjustments in the activity of the leg and trunk muscles when dealing with body perturbations. Anticipatory postural adjustments (APAs) control the position of the center of mass of the body by activating

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Lei Zhang, Andreas Straube and Thomas Eggert

Unexpected small perturbations during reaching movements are normally compensated for automatically. Previous studies of such perturbations observed that the movement trajectory converges back to the preplanned end position. The question remains whether peripheral mechanisms formed by intrinsic muscle properties and stretch reflex are efficient for compensating for such perturbations. Even though this is suggested by a threshold position control model highlighting the role of peripheral mechanisms under central control in movement generation, it is neither developed nor extensively tested for this capability. The present study tests how this model can account for the compensation during single-joint fast reaching. Motor responses to transient, unpredictable, small perturbations at different movement phases were measured and compared with the model predictions. The results show good agreement concerning kinematic and dynamic responses. Simulations with altered mechanical parameters of the model suggest that reflexive responses are well tuned to the intrinsic muscle properties. We conclude that under central control, peripheral mechanisms cope efficiently with small transient perturbations.

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Nicolas Termoz, Luc Martin and François Prince

The aim of this study was to assess postural response efficiency to a self-initiated perturbation using an original method based on the inverted pendulum model. Eight young subjects were asked to perform bilateral arm raising and lowering at 3 different speeds while standing on a force plate. The time necessary to recover a steady state following the movement was computed by analyzing the time evolution of the coefficient of determination between the center of pressure and center of mass difference variable (COP-COM) and the horizontal acceleration of the COM. Results show a spatial reorganization (hip strategy) of the segments following the perturbation and a strong influence of the linear relationship to the arm velocity. However, the conditions of arm velocity did not have any effect on the time response of the postural control, suggesting that this parameter would be an invariant characteristic of the movement. These results support the existence of an internal representation of the inertial constraints related to the movement execution.

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David Clizbe and Nancy Getchell

The third in a series of studies investigating the development of multilimb coordination in children, this study investigates the ability to period correct, or resynchronize limbs after a temporal perturbation. Participants performed single (clap, walk) and dual (simultaneously clap and walk) motor tasks to a metronome, which was randomly perturbed (either increase or decrease in speed). In the walk/metronome coupling, a significant interaction existed in relative phase error between age group and cycle with less relative phase error on the third and forth cycle with increased age. In the clap/metronome, a main effect existed for cycle (increasing with cycle) and age (decreasing with age), but no interactions existed. Neither task (single or dual) nor direction of perturbation (speed increase/decrease) had a statistical effect. The results suggested that developmental trajectories may exist in period correction processes; further research examining continuous data over longer collection periods should be performed to confirm this finding.

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Zakariya Nawasreh, David Logerstedt, Adam Marmon and Lynn Snyder-Mackler

chance to restore normal knee function after reconstruction surgery. 18 , 19 The current treatment recommendation for patients with an ACL rupture planning to delay surgery is to participate in strength training augmented with perturbation training program. 20 , 21 Perturbation training is a type of

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Valeria Rosso, Laura Gastaldi, Walter Rapp, Stefan Lindinger, Yves Vanlandewijck, Sami Äyrämö and Vesa Linnamo

trunk plays also a major role in maintaining athlete’s stability for a proper balancing on the sit-ski while skiing. Trunk stability can be defined as the equilibrium recovery after a perturbation ( Zazulak, Hewett, Reeves, Goldberg, & Cholewicki, 2007 ) and requires complex muscle coordination

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Renato Claudino, Marcio José dos Santos and Giovana Zarpellon Mazo

activation to body perturbations in the standing position ( Inglin & Woollacott, 1988 ; Maki, Edmondstone, & McIlroy, 2000 ; Maki, Perry, Norrie, & McIlroy, 1999 ; Melzer, Benjuya, & Kaplanski, 2004 ). For instance, when exposed to postural perturbations, older adults have shown an increase in the

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Chadwick Debison-Larabie, Bernadette A. Murphy and Michael W.R. Holmes

head perturbations has focused on flexion/extension head movements, 6 – 9 with some seated whiplash protocols investigating lateral perturbations. 10 , 11 Perturbations that cause lateral bend and rotational head motion are required to fully comprehend potential sex differences in neuromuscular

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Michiel Punt, Sjoerd M. Bruijn, Ingrid G. van de Port, Ilona J.M. de Rooij, Harriet Wittink and Jaap H. van Dieën

-prone stroke survivors. Here, we define stable gait as gait that does not result into falls despite of perturbations. 6 In comparison to conventional treadmill training of gait stability, perturbation-based training (PBT) may offer a more ecologically valid training approach. Meaning that the exercises

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Jeffrey D. Simpson, Ethan M. Stewart, Anastasia M. Mosby, David M. Macias, Harish Chander and Adam C. Knight

ground contact. 2 , 3 Landing from a jump requires ankle plantar flexion and in some cases ankle inversion to attenuate large and rapid impulse loads when landing, 4 , 5 which can initiate the mechanism of a LAS. 6 , 7 The rapid and unexpected (UE) joint perturbations that can occur when landing on 1