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Introduction: The purpose of this study was to investigate whether the anticipation of a mechanical perturbation applied to the arm during a reach-to-grasp movement elicits anticipatory adjustments in the reach and grasp components. Additionally, we aimed to evaluate whether anticipatory adjustments in the upper limb might be global or specific to the direction of the perturbation. Methods: Thirteen healthy participants performed reach-to-grasp with perturbations randomly applied to their dominant limb. Participants were presented with three types of trials: unperturbed (control), trials perturbed in a predictable manner (either Up or Down), or perturbed in a partially predictable manner (knowledge about the perturbation but not its specific direction). EMG activity of 16 muscles, as well as the kinematics of wrist, thumb, and index finger, were acquired and analyzed. Results and discussion: When the perturbation was expected, EMG activity of the triceps and pectoralis major muscles significantly increased about 50 – 200 ms before the perturbation onset. Peak acceleration of the reach was significantly higher and occurred earlier relative to control trials. Similar adjustments were observed in the grasp kinematics, reflected as significantly shorter time to peak aperture velocity and acceleration, as well as in increased activity of flexor and extensor digitorum 100–200 ms before perturbation onset. In summary, our data demonstrate that knowledge of an upcoming perturbation of reach during reach-to-grasp action triggers anticipatory adjustments not only in the muscles controlling the reach component, but also in those controlling grasp. Furthermore, our data revealed that the preparatory activations were generalized, rather than direction specific. [ABSTRACT FROM AUTHOR]

Introduction: Ankle stiffness is a factor that contributes to maintaining balance and counteracts the forces of gravity as the body sways. Stability while standing quietly depends on its value. Intrinsic ankle stiffness refers to (i) the passive resistance provided by the structural components of the ankle joint itself, such as the ligaments and joint capsules, (ii) a property of the joint that remains constant regardless of the external forces applied, (iii) a characteristic that affects the stability and control of the ankle joint. The aim is to present compilation of the results published in the researchers' work makes it possible to analyze changes in the value of ankle stiffness for perturbations of different amplitude. Material and Methods: The review is based on articles identified through searches of Pubmed, Web of Science, and Scopus. There were no restrictions on the publication date. The Boolean search strategy was used. Results: Ankle stiffness changes with increasing sway amplitude. Its values are greater for perturbations of smaller amplitudes and, therefore, cannot be represented by a single value. Passive stiffness reduces sway and allows time for the active system to respond. The interaction of these two mechanisms ensures the stability of an upright posture. Conclusions: Ankle stiffness is a parameter that can be applied in clinical practice. The exact determination of the range of stiffness values is a useful tool to define a motor organization/reorganization. [ABSTRACT FROM AUTHOR]