Reach to grasp kinematics and EMG analysis of C6 quadriplegic subjects

The aim of the present study was to assess the kinematics and the muscular activity of the upper limb of subjects suffering from a spinal cord injury (SCI) at the C6 level during a grasping task. Data were compared to a control group composed of able-bodied subjects. The electrical activity of six major upper limb muscles and 3D motion of the arm were recorded. Results showed higher relative muscular solicitation for C6 patients especially for deltoïdus posterior and the pectoralis major and modifications of the range of motion of the corresponding joint angles. It appeared that, for C6 SCI subjects, the role of shoulder complex is highly relevant to initiate and control upper extremity movement, and so is important for their autonomy. Such data may be used to help clinician in decision making, e.g. for reconstructive surgery by musculotendinous transfer.

A clarification of Pouydebat et al., 2008, evolution of grasping among anthropoids

Several statements by Pouydebat et al. (2008) do not adequately represent views of authors cited, in part because they reflect confusion in the literature about terminology regarding precision gripping. We address these problems, by tracing definitions of precision grips through the literature on manipulative behaviour and identifying the grip that is central to the Pouydebat et al. (2008) study. This allows us to offer a clarification of the statements by Pouydebat et al. (2008) regarding the sequence of appearance of human grip capabilities and possible morphological correlates to these capabilities in extant species.

Upper limb muscle forces during a simple reach-to-grasp movement: a comparative study

Muscle force knowledge during reaching is an important research field and tools development for measuring those forces is a challenging task, especially for clinical routines. The purpose of this study was, during a simple reach-to-grasp movement, to compare forces estimation from a Hill-type model and from the EMG-to-Force Processing (EFP) method. Ten healthy male volunteers were tested. Surface EMG signals were recorded from deltoid scapular, deltoid clavicular, triceps brachii, and biceps brachii. Ten repeated measures of right upper limb kinematics had been recorded. Three reaching distances were tested: 20, 30, and 40 cm. Muscle activations were calculated and forces were estimated by the two methods. Correlations and low RMS error found between the two methods indicate that EFP is a good way to estimate muscle forces for this kind of movement. This knowledge is essential in order to integrate these forces in reaching models developed nowadays in robotic, rehabilitation, and ergonomics field of research.

Synergies during reach-to-grasp: a comparative study between healthy and C6-C7 quadriplegic subjects

Analysis of functional capacities modifications after spinal cord injuries may have an interest in clinical rehabilitation programs. In this framework, this study is focused on the analysis of motor synergies i.e. how the upper-limb degrees of freedom (DOFS) are organized when considering C6-C7 quadriplegic subjects performing a reaching task. A previous work has shown that sharing patterns between DOFS are preserved. Using the uncontrolled manifold hypothesis (UCM), we investigate the second aspect of motor synergies i.e. how performance is allowed to show both stability against perturbations and flexibility to solve concurrent tasks. This procedure allows to evaluate the stabilization of a specific and selective performance variable through the variability of joint angles. In the present study, the wrist 3D path was considered and the variability of its trajectory is decomposed into two parts: one which does not affect the value of this performance variable (goal equivalent variance or GEV) and one which does (non goal equivalent variance or NGEV). Results showed that quadriplegic subjects present the same variance decomposition than healthy subjects suggesting that, despite the motor deficiency, flexibility is still allowed during movement execution.

Muscle activation during a reach-to-grasp movement in sitting position: influence of the distance

The purpose of this study was to examine the influence of the reach distance on the muscle activation during a reach-to-grasp movement in the sitting position. Ten healthy male volunteers were tested. Surface EMG were recorded for the deltoid scapular, the deltoid clavicular, the triceps brachii, the biceps brachii and the brachioradialis. These muscles have been selected for their contribution to the cylindrical palmar prehension motion in the sagittal plane. Three distances have been tested: 20, 30 and 40 cm. For each distance, ten repeated measures have been recorded. From this in vivo data, the repeatability of the protocol has been tested. For this, relative (ICC) and absolute (SEM) reliabilities are determined in order to evaluate the intra operator repeatability of this protocol. It appears that the ICC values obtained are between 0.78 and 0.99 in all the conditions (15 conditions corresponding to three distances and five muscles). The intra operator repeatability is thus confirmed. From these surface EMG recordings the muscle activations have been calculated as the iEMG value. It appears that the muscle activation is greater with increased distances. The results contribute to the identification of the levels of muscle activation amplitude during a simple reach-to-grasp movement that is common in prehension research. This knowledge is essential in order to calculate the muscle forces and to integrate these forces in the prehension models developed nowadays in the robotic, rehabilitation, ergonomics field of research.