The interest in sports monitoring, especially in investigating and understanding human body movements, called biomechanics, has been grown rapidly over the last few decades. Another big research area beside the biomechanics is physiological measurement, which quantifies energy systems and performance of the muscles. This usually requires direct measures of the athlete, whereby the biomechanics is focussed on performance characteristics such as include the kinematics, kinetics, force, work, energy and power.
With more and more technical systems available (i.e. video motion capture systems) it is easier today to investigate and transfer a body movement into a computer movement model than it was ten years ago. However a lot of manual processing is still required to gather results from these systems. A new kind of measuring device, accelerometer based sensors (MEMS1), detect acceleration (movements) in all directions (x, y and z). These small, wireless sensors also contain gyroscopes, which measure rotation in three axes.
Small sports monitoring systems are of interest to professional swimmers and their coaches. Devices fitted on a swimmer are expected to be small. These devices should not affect the swimmer during the training session and must have an easy to use interface.
A first step in this global goal is to investigate the wall push-off for a swimmer and calculate the velocity profile and the drag coefficients. Wall push-offs (n=34) at different forces (low, medium and full), were performed by two swimmers. One was a retired professional and the other a recreational swimmer. The instrumentation used included a sacrum mounted purpose- built accelerometer, a force plate, synchronised video camera and tethered cable velocity meter. The median of the achieved velocity from the accelerometer for all push-offs was 80% of the tethered device measured velocity. The velocity derived from the acceleration compared to the tethered velocity gave an R2 of 0.77.
The developed method for obtaining the wall push-off velocity from an accelerometer has been proved to be robust. It provides athletes with the opportunity to perform their training at any pool without expensive technical equipment. Future work will be conducted on investigating a whole swimming lap to investigate and extract the intra stroke velocity and therefore the velocity variation during a training session.