Power has been demonstrated to be an early and potent marker of frailty. The measurements currently available are tied to locality. Usually, measurements include single joint movements or movements of only the legs and the resistance is not adjusted for body weight. In this study, a portable method to measure power in the sit-to-stand transfer was developed and tested. Mean power was calculated from the vertical ground reaction force of body weight, the difference between height in a sitting and in an upright position and the time taken to stand up. The results of this power measurement were compared with an isokinetic force measurement, the "Nottingham power rig", and measurement of physical performance in a five-repetition chair rise (five-chair rise). A convenience sample of 33 healthy elderly subjects [mean (SD) age: 67.8 (6.7) years; 17 men, 16 women] was included. Measurement of power during the sit-to-stand transfer showed good correlation to isokinetic force measurement (r=0.68) and to the "Nottingham power rig" (r=0.6). Correlation to five-chair rise was poor (r=-0.08). In conclusion, the study shows that the method presented is able to measure power during performance of a daily task. The poor correlation between the introduced measurement and the five-chair rise suggests that it might be able to detect decline in muscle function earlier by the introduced measurement than by measurement of the functional status. As it is inexpensive and portable, its use in clinical practice and research contexts, including home-bound individuals, is feasible.

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The paper presents the vibration analysis and the evaluation of dynamic stresses in flexible multibody systems, and their parameter optimization using symbolic-numeric methods. Based on the fundamentals of multibody system modeling the force method and the deformation method are described and the latter one is extended to include the static and dynamic responses of the structure. Performance criteria are defined for optimization. The overall design process is supported by appropriate software for all steps of analysis and optimization. The application of the approach is devoted to railway dynamics. For the analysis of the dynamic stresses in a railway wheelset the extended deformation approach is used. The simulation results indicate that the durability of the design of the wheelset under consideration is satisfactory. The vertical vibrations of the passenger coach with rigid wheelsets and a flexible bogie frame results in acceleration amplitudes of the carbody which may cause a brumming or droning noise. The substitution of the rigid wheelsets by radialelastic ones reduces these amplitudes considerably. An optimization of spring and damper coefficients of the model with radialelastic wheels results in reduced droning noise of such a passenger coach and lower force level between wheel and rail. The symbolic approach is especially highlighted for the simulation at different vehicle speeds and the optimization of the suspension parameters.

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