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Yumeng Li, Melissa A. Mache and Teri A. Todd

physiological complexity. 18 Multiscale entropy is a nonlinear analysis tool to quantify complexity or irregularity of a time-series signal over multiple time scales. Compared with approximate entropy and sample entropy, multiscale entropy quantifies the overall complexity of a system and allows researchers to

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Marcel Mutsaarts, Bert Steenbergen and Harold Bekkering

Anticipatory planning was examined in detail for a complex object manipulation task by capitalizing on both the complexity and the number of elements in the movement sequences in seven individuals with hemiparetic cerebral palsy (HCP) and seven left-handed control participants. Participants had to grasp a hexagonal knob using one of five possible grasping patterns as quicklly as possible following a starting cue (condition I), and sometimes, they had to rotate it subsequently either 60˚ or 120˚ clockwise or counterclockwise (condition II). In the first condition, the HCP participants appear to anticipate the comfort of the different grasping patterns before movement onset, as controls did. However, when the task consisted of more than one movement part, HCP participants did not complete their planning processes before movement onset, which was contrary to controls. Instead, the results suggest that they use a step-by-step planning strategy, that is, they planned the latter parts of a movement sequence as the movement unfolds. The results are discussed in the light of possible capacity limitations of an internal model for grip selection, and a recent model on the planning and on-line control of movement performance.

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Fatemeh Azadinia, Ismail Ebrahimi-Takamjani, Mojtaba Kamyab, Morteza Asgari and Mohamad Parnianpour

), 731 – 735 . PubMed ID: 25737236 doi:10.1016/j.gaitpost.2015.01.008 Rhea , C.K. , Silver , T.A. , Hong , S.L. , Ryu , J.H. , Studenka , B.E. , Hughes , C.M. , & Haddad , J.M. ( 2011 ). Noise and complexity in human postural control: Interpreting the different estimations of entropy

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Anne Sofie B. Malling, Bo M. Morberg, Lene Wermuth, Ole Gredal, Per Bech and Bente R. Jensen

, Bode, & Wermuth, 2014 ; Uhrbrand, Stenager, Pedersen, & Dalgas, 2015 ). Physical rehabilitation for persons with PD is therefore important to minimize motor deficits due to disease progression. The complexity of a motor task may be defined by the number of task components and the connections between

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Jay P. Mehta, Matthew D. Verber, Jon A. Wieser, Brian D. Schmit and Sheila M. Schindler-Ivens

We used functional magnetic resonance imaging (fMRI) to record human brain activity during slow (30 RPM), fast (60 RPM), passive (30 RPM), and variable rate pedaling. Ten healthy adults participated. After identifying regions of interest, the intensity and volume of brain activation in each region was calculated and compared across conditions (p < .05). Results showed that the primary sensory and motor cortices (S1, M1), supplementary motor area (SMA), and cerebellum (Cb) were active during pedaling. The intensity of activity in these areas increased with increasing pedaling rate and complexity. The Cb was the only brain region that showed significantly lower activity during passive as compared with active pedaling. We conclude that M1, S1, SMA, and Cb have a role in modifying continuous, bilateral, multijoint lower extremity movements. Much of this brain activity may be driven by sensory signals from the moving limbs.

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Tiago M. Barbosa, Wan Xiu Goh, Jorge E. Morais and Mário J. Costa

The aim was to examine the variation of linear and nonlinear proprieties of the behavior in participants with different levels of swimming expertise among the four swim strokes. Seventy-five swimmers were split into three groups (highly qualified experts, experts and nonexperts) and performed a maximal 25m trial for each of the four competitive swim strokes. A speed-meter cable was attached to the swimmer’s hip to measure hip speed; from which speed fluctuation (dv), approximate entropy (ApEn) and fractal dimension (D) variables were derived. Although simple main effects of expertise and swim stroke were obtained for dv and D, no significant interaction of expertise and stroke were found except in ApEn. The ApEn and D were prone to decrease with increasing expertise. As a conclusion, swimming does exhibit nonlinear properties but its magnitude differs according to the swim stroke and level of expertise of the performer.

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Vennila Krishnan and Slobodan Jaric

Coordination of the hand grip (G; acting normally to the grasping surface) and load forces (L; acting in parallel) in bimanual static tasks was studied. L symmetry (either the magnitude or direction) and frequency were manipulated in healthy participants (N = 14). More complex tasks (i.e., the higher frequency and/or asymmetric ones) revealed expected deterioration in both the task performance (accuracy of the prescribed L force profiles) and force coordination (G/L ratio and G-L correlation) suggesting importance of L frequency and symmetry in prehension activities. However, the same tasks revealed a more prominent deterioration of interlimb than the within-limb force coordination. This could be interpreted by two partly different and noncompeting neural control mechanisms where the coordination of interlimb forces may be based on ad-hoc and task-specific muscle coordination (often referred to as muscle synergies) while the within-limb coordination of G and L could be based on more stable and partly reflex mechanisms.

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Ludovic Seifert, Dominic Orth, Jérémie Boulanger, Vladislavs Dovgalecs, Romain Hérault and Keith Davids

This study investigated a new performance indicator to assess climbing fluency (smoothness of the hip trajectory and orientation of a climber using normalized jerk coefficients) to explore effects of practice and hold design on performance. Eight experienced climbers completed four repetitions of two, 10-m high routes with similar difficulty levels, but varying in hold graspability (holds with one edge vs holds with two edges). An inertial measurement unit was attached to the hips of each climber to collect 3D acceleration and 3D orientation data to compute jerk coefficients. Results showed high correlations (r = .99, P < .05) between the normalized jerk coefficient of hip trajectory and orientation. Results showed higher normalized jerk coefficients for the route with two graspable edges, perhaps due to more complex route finding and action regulation behaviors. This effect decreased with practice. Jerk coefficient of hip trajectory and orientation could be a useful indicator of climbing fluency for coaches as its computation takes into account both spatial and temporal parameters (ie, changes in both climbing trajectory and time to travel this trajectory).

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Lindsay Warren, Russell Baker, Alan Nasypany and Jeffrey Seegmiller

The core is central to almost all extremity movements, especially in athletics. Running, jumping, kicking, and throwing are dependent on core function to create a stable base for movement. Poor core strength, endurance, stiffness, control, coordination, or a combination thereof can lead to decreased performance and increased risk of injury. Due to the core’s many complex elements, none of which are more or less important than the next, it is imperative that athletic trainers have a systematic and comprehensive plan for assessing and treating patients with stability or motor control dysfunctions of the entire spinal stabilizing system. The purpose of this clinical commentary is to outline the structural (anatomical) components of the core and their functions, establish the elements of core stability (functional), review these elements’ importance in decreasing the risk of injury, and discuss the application of this information in athletic training.

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Sergio Jiménez-Rubio, Archit Navandar, Jesús Rivilla-García and Victor Paredes-Hernández

players from the diagnosis of the injury until return to play. The players would then perform 13 on-field items of the rehabilitation and readaptation program (Table  2 ) in a progressive manner, which are arranged in an increasing order of complexity. When the player completes each of the 13 items