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Tarkeshwar Singh, Vladimir M. Zatsiorsky and Mark L. Latash

The effects of muscle fatigue on the stability of precision grasps are not well known. The purpose of the current study was to investigate the effects of exercise-induced fatigue of a digit on prehension synergies in a static precision grasp. One group of participants performed the fatiguing exercise using the thumb (group-thumb) and the second group performed the exercise using the index finger (group-index). Grasp force and load-resisting force-stabilizing synergies were weaker during fatigue for group-thumb and showed no significant change for group-index. These results indicate that fatiguing the thumb compromises the stability of the precision grasp more than when the index finger is fatigued. Our results support the idea of hierarchical organization of prehension control. We proffer an explanation of our results based on two control constructs: a) Principle of superposition. This principle states that prehension can be viewed as a superposition of two independent processes controlling the slip and the tilt of the object respectively; and b) The referent configuration hypothesis. According to this hypothesis, the neural control of actions is associated with defining a set of referent values for task-related coordinates (given an external force field) defined as the referent configuration.

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Todd C. Pataky, Greg P. Slota, Mark L. Latash and Vladimir M. Zatsiorsky

During power grasp, the number of local force maxima reflects either the central nervous system’s preferential use of particular hand regions, or anatomical constraints, or both. Previously, both bimodal and trimodal force maxima have been hypothesized for power grasp of a cylindrical handle. Here we measure the number of local force maxima, with a resolution of 4.8°, when performing pushing and pulling efforts in the plane perpendicular to the cylinder’s long axis. Twelve participants produced external forces to eight targets. The number of contacts was defined as the number of local maxima exceeding background variance. A minimum of four and a maximum of five discrete contacts were observed in all subjects at the distal phalanges and metacarpal heads. We thus reject previous hypotheses of bimodal or trimodal force control for cylindrical power grasping. Since we presently observed only 4–5 contacts, which is rather low considering the hand’s kinematic flexibility in the flexion plane, we also reject hypotheses of continuous contact, which are inherent to current grasping taxonomy. A modification to current grasping taxonomy is proposed wherein power grasp contains separate branches for continuous and discrete contacts, and where power and precision grasps are distinguished only by grasp manipulability.

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Beatriz H. Thames and Stacey L. Gorniak

diabetic patient ability to self-monitor their capillary blood sugar, by both affecting the precision grasp need to hold and use a lancet, but also the ability of a patient to pierce the skin with the lancet. With respect to these issues, safety lancets may be the best option for self-lancing in this

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Gabriel Andrade Paz, Lohanne Almeida, Larissa Ruiz, Sabrina Casseres, Giovanna Xavier, João Lucas, Haroldo Gualter Santana, Humberto Miranda, Scott Bonnette and Jeffrey Willardson

G , Vesia M , Isayama R , Gunraj C , Chen R . Increases in motor cortical excitability during mirror visual feedback of a precision grasp is influenced by vision and movement of the opposite limb . Neurosci Lett . 2018 ; 681 : 31 – 36 . PubMed ID: 29787788 doi: 10.1016/j.neulet.2018