Development of a French Isometric Strength Normative Database for Adults Using Quantitative Muscle Testing

International audienceOBJECTIVE: To establish a normative database for isometric strength measured by quantitative muscle testing (QMT) for a French adult population.DESIGN: Measurement of maximal voluntary isometric contraction.SETTING: Four clinical centers involved in neuromuscular disorders.PARTICIPANTS: A total of 315 healthy adults (147 men, 168 women) ages 20 to 80 years.INTERVENTIONS: Not applicable.MAIN OUTCOME MEASURE: Isometric torque values of 14 muscle functions (13 bilaterally and neck).RESULTS: This study led to the development of a French isometric strength normative database for adults measured by QMT. For each muscle function, predictive regression models using age, sex, and weight are proposed. Some methodologic issues concerning strength measurement are discussed.CONCLUSIONS: This database can be used to compute relative deficits in muscle strength for 27 muscle functions and also to estimate composite scores for follow-up of patients either during the natural history of their disease or during a therapeutic trial

Two stages and three components of the postural preparation to action

Previous studies of postural preparation to action/perturbation have primarily focused on anticipatory postural adjustments (APAs), the changes in muscle activation levels resulting in the production of net forces and moments of force. We hypothesized that postural preparation to action consists of two stages: (1) Early postural adjustments (EPAs), seen a few hundred ms prior to an expected external perturbation; and (2) APAs seen about 100 ms prior to the perturbation. We also hypothesized that each stage consists of three components, anticipatory synergy adjustments seen as changes in co-variation of the magnitudes of commands to muscle groups (M-modes), changes in averaged across trials levels of muscle activation, and mechanical effects such as shifts of the center of pressure. Nine healthy participants were subjected to external perturbations created by a swinging pendulum while standing in a semi-squatting posture. Electrical activity of twelve trunk and leg muscles and displacements of the center of pressure were recorded and analyzed. Principal component analysis was used to identify four M-modes within the space of muscle activations using indices of integrated muscle activation. This analysis was performed twice, over two phases, 400-700 ms prior to the perturbation and over 200 ms just prior to the perturbation. Similar robust results were obtained using the data from both phases. An index of a multi-M-mode synergy stabilizing the center of pressure displacement was computed using the framework of the uncontrolled manifold hypothesis. The results showed high synergy indices during quiet stance. Each of the two stages started with a drop in the synergy index followed by a change in the averaged across trials activation levels in postural muscles. There was a very long electromechanical delay during the early postural adjustments and a much shorter delay during the APAs. Overall, the results support our main hypothesis on the two stages and three components of the postural preparation to action/perturbation. This is the first study to document anticipatory synergy adjustments in whole-body tasks. We interpret the results within the referent configuration hypothesis (an extension of the equilibrium-point hypothesis): The early postural adjustment is based primarily on changes in the co-activation command while the APAs involve changes in the reciprocal command. The results fit an earlier hypothesis that whole-body movements are controlled by a neuromotor hierarchy where each level involves a few-to-many mapping organized to stabilize its overall output