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Jürgen Konczak, Kai Brommann, and Karl Theodor Kalveram

Knowledge of how stiffness, damping, and the equilibrium position of specific limbs change during voluntary motion is important for understanding basic strategies of neuromotor control. Presented here is an algorithm for identifying time-dependent changes in joint stiffness, damping, and equilibrium position of the human forearm. The procedure requires data from only a single trial. The method relies neither on an analysis of the resonant frequency of the arm nor on the presence of an external bias force. Its validity was tested with a simulated forward model of the human forearm. Using the parameter estimations as forward model input, the angular kinematics (model output) were reconstructed and compared to the empirically measured data. Identification of mechanical impedance is based on a least-squares solution of the model equation. As a regularization technique and to improve the temporal resolution of the identification process, a moving temporal window with a variable width was imposed. The method's performance was tested by (a) identifying a priori known hypothetical time-series of stiffness, damping, and equilibrium position, and (b) determining impedance parameters from recorded single-joint forearm movements during a hold and a goal-directed movement task. The method reliably reconstructed the original angular kinematics of the artificial and human data with an average positional error of less than 0.05 rad for movement amplitudes of up to 0.9 rad, and did not yield hypermetric trajectories like previous procedures not accounting for damping.

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Nathan Harrison, W. Zach Garrett, and Mark K. Timmons

The shoulder girdle is a highly mobile and complex mechanism. A shoulder girdle’s motion results from coordinated muscle activity. 1 , 2 The scapula motion pattern during arm elevation is upward rotation, external rotation, and posterior tilting, combined with clavicular elevation and retraction

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Barry S. Mason, Viola C. Altmann, and Victoria L. Goosey-Tolfrey

Paralympic sports, a classification system exists in order to minimize the impact of impairment on the outcomes of competition. 2 Classification in WR is largely dependent on the physical assessment of trunk and arm function. Point scores between 0 and 1.5 are awarded to represent trunk function. Both arms

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Allison J. Nelson, Patrick T. Hall, Katherine R. Saul, and Dustin L. Crouch

is routed over the superior aspect of the shoulder (eg, using pulleys and/or Bowden cables), and attached on the lateral aspect of the arm to a cuff worn around the arm. We computed exoskeleton design parameters to offset 100% of the negative shoulder elevation moment due to gravity in static

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Danny M. Pincivero, Rachael R. Polen, and Brittany N. Byrd

mass, percentage body fat, arm skinfold thickness, and peak elbow flexor/extensor force (concentric and eccentric), were sampled from 30 healthy young adults (Table  1 ). All participants were physically active, as they reported performing various types of exercise at least 2 days per week for

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Jared R. Fletcher and Brian R. MacIntosh

Direct measurement of muscle forces in vivo is highly invasive, 1 so muscle forces are typically estimated from measurement of joint moments. 2 , 3 Estimating muscle forces from joint moments requires knowledge of the muscle/tendon moment arm, that is, the perpendicular distance from the joint

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Steven J. Obst, Lee Barber, Ashton Miller, and Rod S. Barrett

Estimates of in vivo Achilles tendon (AT) force are needed to measure tendon mechanical properties as a function of the measured net ankle joint torque, and to understand AT function using musculoskeletal modeling approaches. The AT moment arm is required to convert the measured external ankle

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Kayla J. Nuss, Joseph L. Sanford, Lucas J. Archambault, Ethan J. Schlemer, Sophie Blake, Jimikaye Beck Courtney, Nicholas A. Hulett, and Kaigang Li

values reported by wearable devices ( Dannecker et al., 2013 ; Ferguson et al., 2015 ; Lee et al., 2014 ; Sasaki et al., 2015 ). Part of this error may be due to poor contact of the device against the body ( “ActionSleeve Armband for Apple Watch,” n.d. ). In addition to the wrist, the upper arm is

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Stijn Schouppe, Jessica Van Oosterwijck, Jan R. Wiersema, Stefaan Van Damme, Tine Willems, and Lieven Danneels

important part of the motor control system, which plays a paramount role for attaining and retaining optimal balance and postural control ( Hodges & Moseley, 2003 ). In this regard, movement preparation patterns of the trunk muscles prior to peripheral movements, for instance, rapid arm movements (RAMs

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Michael E. O’Connell, Kyle E. Lindley, John O. Scheffey, Alex Caravan, Joseph A. Marsh, and Anthony C. Brady

changes was observed in a study of the acute effects of overload and underload implements in cricket fast bowling. 14 A later study found significant effects of throwing 4- through 7-ounce (113- through 198-g) ball weights on pitched ball velocity, kinematic velocities, and arm joint kinetics with minor