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Estimating propulsive forces in swimming from three-dimensional kinematic data
1Division of Sport Science, Manchester Metropolitan University, Alsager, Stoke-on-Trent, UK.
Journal of Sports Sciences
|December 1, 1995
Summary
Quantifying measurement error in swimming propulsive forces is crucial. Errors in hand speed and orientation angles (alpha and psi) significantly impact hydrodynamic force calculations, but averaging multiple measurements reduces uncertainty.
Area of Science:
- Biomechanics
- Fluid Dynamics
- Sports Science
Background:
- Propulsive forces are key to swimming performance.
- Accurate measurement of these forces is essential for research and training.
- Previous methods for calculating forces from kinematic data have potential for error.
Purpose of the Study:
- To quantify the measurement error (uncertainty) in propulsive forces calculated from kinematic data.
- To assess the impact of errors in digitized landmarks on force calculations.
- To evaluate methods for reducing measurement error in swimming analysis.
Main Methods:
- Ten operators digitized underwater video of breaststroke arm action.
- Three-dimensional coordinates of four hand landmarks were obtained using DLT algorithm at 50 Hz.
- Hydrodynamic forces (FR) were calculated using hand orientation angles (alpha, psi) and force coefficients.
Main Results:
- Errors in alpha and psi angles led to average errors of 27% and 20% in lift and drag coefficients, respectively.
- Combined with a 6% hand speed error, this resulted in an average 26% error in propulsive force (FR).
- Averaging 10 measurements reduced these errors by a factor of the square root of 10.
Conclusions:
- Measurement errors in kinematic data significantly affect hydrodynamic force calculations in swimming.
- Researchers must report estimated errors and methods used to reduce them.
- Averaging multiple measurements is a viable strategy to improve the accuracy of propulsive force calculations.