Increasing joint stiffness by cocontraction of antagonist muscles and compensatory reflexes are neural strategies to minimize the impact of unexpected perturbations on movement. Combining these strategies, however, may compromise steadiness, as elements of the afferent input to motor pools innervating antagonist muscles are inherently negatively correlated. Consequently, a high afferent gain an...

purpose: this study aimed to examine the differences in the co-activation of the rectus femoris (rf) and biceps femoris (bf) using the co-contraction index (ci) in aquatic and land environments during a drop-landing task in active and non-active females. methods: in this casual-comparison study, 10 active and 10 non-active females volunteered to participate. the ci was calculated from recorded ...

It has been proposed that the control signals underlying voluntary human arm movement have a "complex" nonmonotonic time-varying form, and a number of empirical findings have been offered in support of this idea. In this paper, we address three such findings using a model of two-joint arm motion based on the lambda version of the equilibrium-point hypothesis. The model includes six one- and two...

BACKGROUND Unloading knee braces often are used after tibiofemoral articular cartilage repair. However, the experimental basis for their use in patients with normal tibiofemoral alignment such as those undergoing cartilage repair is lacking. QUESTIONS/PURPOSES The purpose of this study was to investigate the effect of varus and valgus adjustments to one commercially available unloader knee br...

OBJECTIVE: To determine if functional performance is impaired in individuals with self-reported chronic ankle instability. DESIGN AND SETTING: We used a between-groups design to assess 3 functional variables. All data were collected at a Division III college and a military academy. Before testing, all subjects performed a 5-minute warm-up, followed by a series of stretches for the lower extremi...

We investigate the relation between grip force and grip stiffness for the human hand with and without voluntary cocontraction. Apart from gaining biomechanical insight, this issue is particularly relevant for variable-stiffness robotic systems, which can independently control the two parameters, but for which no clear methods exist to design or efficiently exploit them. Subjects were asked in o...

1. Stiff-person syndrome (SPS) is an autoimmune disease characterized by muscle rigidity, episodic muscle spasms, as well as continuous cocontraction of agonist and antagonist muscles. 2. Although a criterion for diagnosis of SPS, anti– glutamic acid decarboxylase (anti-GAD) antibodies can be negative in up to 40% of patients. In absence of antibodies, characteristic EMG findings of continuous ...

Inverse dynamics methods for muscle forces prediction are globally unable to predict antagonistic activity during a joint motion. This is due to a lack of physiological information describing how forces are shared between flexors and extensors. The aim of this study is the definition and the use of a new EMG-based cocontraction ratio in an inverse dynamics muscle forces prediction approach appl...

We investigated adaptation to simple force field scaling to determine whether the same strategy is used as during adaptation to more complex changes in the mechanical environment. Subjects initially trained in a force field, consisting of a rightward lateral force with a parabolic spatial profile (PF). The field strength was then unexpectedly increased or decreased (DeltaPF) for repeated sets o...