This paper introduces a prototype audio-biofeedback system for balance improvement through the sonification using trunk kinematic information. In tests of this system, normal healthy subjects performed several trials in which they stood quietly in three sensory conditions while wearing an accelerometric sensory unit and headphones. The audio-biofeedback system converted in real-time the two-dimensional horizontal trunk accelerations into a stereo sound by modulating its frequency, level, and left/right balance. Preliminary results showed that subjects improved balance using this audio-biofeedback system and that this improvement was greater the more that balance was challenged by absent or unreliable sensory cues. In addition, high correlations were found between the center of pressure displacement and trunk acceleration, suggesting accelerometers may be useful for quantifying standing balance.

Abstract-In this paper, we propose a device for the Position and Orientation (P&O) reconstruction of human segmental locomotion tasks. It is based on three mono-axial accelerometers and three angular velocity sensors, geometrically arranged to form two orthogonal terns. The device was bench tested using step-by-step motorbased equipment. The characteristics of the six channels under bench test conditions were: crosstalk absent, non linearity 0,

Abstract-The analysis of the mechanics of the musculo-skeletal system during the execution of a motor task requires the determination of the instantaneous position and orientation of the body segments involved in relation to an inertial system of reference. By using adequately assembled uniaxial accelerometric sensors, an easy-to-manage measurement system can be obtained that estimates the three-dimensional position and orientation (P&O) of a body segment through an appropriate analytical model. However, the extent to which experimental errors, in particular accelerometers (ACs) assembly inaccuracies, affect such estimation has never been systematically investigated. This paper systematically analyzes the sensitivity of analytical models of body segment P&O reconstruction through a six-AC system and a nine-AC system to different sources of experimental error. We simulated and statistically assessed the performance of these models in the case of body segment motions typical of movements under muscular control.The results obtained indicated that the inaccuracy in the orientation of the individual AC's active axes and the offset error in the AC responses were the major sources of P&O estimation errors. In particular, no accurate estimation of position was possible with the analytical models analyzed. Under the motion conditions simulated in this study, no substantial advantages were found in using a nine-AC system rather than a six-AC system.Considering that the magnitudes of the simulated experimental errors were quite low ( 0.1 deg: AC's orientation; 10 4 m: uncertainty of the distance between two ACs; 10 2 ms 2 : random error; 0.5 10 2 ms 2 : offset error), the results indicate that none of the two ACs systems analyzed is suitable for body segment P&O estimation in routine biomechanical applications.Index Terms-accelerometer, accuracy, human movement analysis, simulation, 3-D rigid body position and orientation.

A clinical tool and an associated test that can assess fall-risk in elderly patients have been designed. The clinical tool was based on a wearable device with accelerometers and rate gyroscopes to identify trunk kinematic parameters. The test was based on a posturography protocol with different constraints and statistical analysis of the kinematic parameters. Statistical clustering based on the Mahalanobis distance was carried out using three groups of 30 subjects (1, age < 65 years; 2, age > or = 65 years and 3, age > or = 65 years and a fall history). The method was statistically validated using three groups of 100 subjects. The test allowed discrimination of elderly subjects with a high fall-risk with high specificity > or = 0.930 and sensitivity > or = 0.939.

[...]