THE INFLUENCE OF TIMING IN MOVEMENT EFFICIENCY
AbstractINTRODUCTION The vertical movement of the human body is visible in almost all sports. Even in the case of sports like running, cycling, and long jumping where the aim is to achieve horizontal distance, vertical motion is obvious and highly essential in performing the movement. Components of vertical motion contribute to the total energy needed for the movement. In this study we analyze efficiency of the vertical motion components and discuss timing as one of the factors influencing the energy consumption of the movement. Efficiency is defined as the quotient of the work output divided by the energy needed to perform and given as η= Wout / Ein where Wout is work per formed on a mass. In both the ascending or descending motions. Ein is energy produced by muscles to do so. In classical mechanics efficiency is calculated as positive for ascent and negative for descent. METHOD A computer simulation of human motion beginning in a standing position, moving down to a squatting position and vice versa was performed. The motion was constructed symmetrically for upward and downward movements, so that a downward movement can be described as an upward movement with time reversed (t -> -t). For this simulation we used the commercial software SDS Version 3.5 of Solid Dynamics. The human body is approximated by the Hanavan model using anthropometric data of a male person. Similar simulations are also done in the following movements: a) raising the body off the ground with one leg on a bench b) alternate stepping with one leg then the other, keeping the same foot position when on the ground C) lifting weights with the arms flexed In the second stage of the study we obtained real movement data using 3 cameras and a 3D Peak Performance digitizing system. This data and the anthropometry of our subjects were included into an inverse dynamics analysis, using SDS to calculate the efficiency. RESULTS Figure 1 represents the efficiency simulation for a squatting motion at difference timings. The graph shows for a downward or upward movement with a duration of 0.75 seconds, which result in an efficiency of 0.674. For slower movements η Coverges below 0.9. Our experiment shows efficiencies in the same range as the simulation. A detailed analysis of the various simulations demonstrates that efficiency is dependent on timing. Conclusion The above results suggest that the optimizing of efficiency helps to reduce energy consumption of the vertical motion. This subsequently provides more energy needed for the horizontal motion and thus the complete performance. Such effects seem unimportant for a single movement, but with thousands of repetitions in a cyclic motion the minute energy conservation adds up to a substantial amount and consequently influences the performance.
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