Human sit-to-stand transfer modeling towards intuitive and biologically-inspired robot assistance

© 2016, Springer Science+Business Media New York. Sit-to-stand (STS) transfers are a common human task which involves complex sensorimotor processes to control the highly nonlinear musculoskeletal system. In this paper, typical unassisted and assisted human STS transfers are formulated as optimal feedback control problem that finds a compromise between task end-point accuracy, human balance, energy consumption, smoothness of motion and control and takes further human biomechanical control constraints into account. Differential dynamic programming is employed, which allows taking the full, nonlinear human dynamics into consideration. The biomechanical dynamics of the human is modeled by a six link rigid body including leg, trunk and arm segments. Accuracy of the proposed modelling approach is evaluated for different human healthy and patient/elderly subjects by comparing simulations and experimentally collected data. Acceptable model accuracy is achieved with a generic set of constant weights that prioritize the different criteria. Finally, the proposed STS model is used to determine optimal assistive strategies suitable for either a person with specific body segment weakness or a more general weakness. These strategies are implemented on a robotic mobility assistant and are intensively evaluated by 33 elderlies, mostly not able to perform unassisted STS transfers. The validation results show a promising STS transfer success rate and overall user satisfaction

Separable functions of wingless in distal and ventral patterning of the Tribolium leg

The gene wingless (wg) in Drosophila is an important factor in leg development. During embryonic development wg is involved in the allocation of the limb primordia. During imaginal disk development wg is involved in distal development and it has a separate role in ventral development. The expression pattern of wg is highly conserved in all arthropods (comprising data from insects, myriapods, crustaceans, and chelicerates), suggesting that its function in leg development is also conserved. However, recent work in other insects (e.g. the milkweed bug Oncopeltus fasciatus) argued against a role of wg in leg development. We have studied the role of wg in leg development of the flour beetle Tribolium castaneum. Using stage-specific staggered embryonic RNAi in wild-type and transgenic EGFP expressing enhancer trap lines we are able to demonstrate separable functions of Tribolium wg in distal and in ventral leg development. The distal role affects all podomeres distal to the coxa, whereas the ventral role is restricted to cells along the ventral midline of the legs. In addition, severe leg defects after injection into early embryonic stages are evidence that wg is also involved in proximal development and limb allocation in Tribolium. Our data suggest that the roles of wg in leg development are highly conserved in the holometabolous insects. Further studies will reveal the degree of conservation in other arthropod groups

Population-based reference values for the 1-min sit-to-stand test

OBJECTIVES: To determine reference values for the 1-min sit-to-stand (STS) test in an adult population. METHODS: Cross-sectional study nested within a nationwide health promotion campaign in Switzerland. Adults performed the STS test and completed questions on demographics and health behavior. RESULTS: 6,926 out of 7,753 (89.3 %) adults were able to complete the STS test. The median number of repetitions ranged from 50/min (25-75th percentile 41-57/min) in young men and 47/min (39-55/min) in young women aged 20-24 years to 30/min (25-37/min) in older men and 27/min (22-30/min) in older women aged 75-79 years. CONCLUSIONS: The reference values support the interpretation of 1-min STS test performance and identification of subjects with decreased lower body muscular strength and endurance

Analysis and decomposition of accelerometric signals of trunk and thigh obtained during the sit-to-stand movement

Piezoresistive accelerometer signals are frequently used in movement analysis. However, their use and interpretation are complicated by the fact that the signal is composed of different acceleration components. The aim of the study was to obtain insight into the components of accelerometer signals from the trunk and thigh segments during four different sit-to-stand (STS) movements (self-selected, slow, fast and fullflexion). Nine subjects performed at least six trials of each type of STS movement. Accelerometer signals from the trunk and thigh in the sagittal direction were decomposed using kinematic data obtained from an opto-electronic device. Each acceleration signal was decomposed into gravitational and inertial components, and the inertial component of the trunk was subsequently decomposed into rotational and translational components. The accelerometer signals could be reliably reconstructed: mean normalised root mean square (RMS) trunk: 6.5% (range 3-12%), mean RMS thigh: 3% (range 2-5%). The accelerometric signals were highly characteristic and repeatable. The influence of the inertial component was significant, especially on the timing of the specific event of maximum trunk flexion in the accelerometer signal. The effect of inertia was larger in the trunk signal than in the thigh signal and increased with higher speeds. The study provides insight into the acceleration signal, its components and the influence of the type of STS movement and supports its use in STS movement analysis

Struck by stroke: A pilot study exploring quality of life and coping patterns in younger patients and spouses

So far, research on quality of life after stroke has focused mainly on elderly patients. This study is targeted at younger stroke patients and their partners, aiming to evaluate stroke impact, as related to coping strategy. For our pilot study, eight patients who had suffered a stroke and four partners completed the Impact of Event Scale questionnaire. The mean age was 47.6 years in patients and 44.5 years in partners. The patients' level of activities of daily life was assessed using the Barthel Index. They were then interviewed to obtain information with respect to stroke impact and coping. The Schedule for the Evaluation of Individual Quality of Life procedure was carried out to measure quality of life, and stroke impact was quantified using Visual Analogue Scales. On average, patients scored 19.25 on the Barthel Index. Quality of life had deteriorated by 20.1% in patients, whereas partners did not show a decline in quality of life. However, well-being was inversely correlated among patients and partners. Accommodative coping was positively correlated with quality of life in both patients and partners. Conversely, assimilation was negatively related to quality of life in patients