Wireless Motion Capture System for Alpine Skiers
Currently, the vast majority of all alpine snow skiers use traditional mechanical bindings due to their reliability and familiarity. However, these bindings have a limited ability to protect the skier from injury, causing the possibility of a season ending ACL injury to loom in the back of any skierís mind [A. Natri ET AL, 1999]. To lower injury rates, these bindings will release the skiers boot but only if a large force is produced on the spring clamps holding the boot in place. Not only does the magnitude of the force have to be large enough to overcome the spring tension, the force must also be along a specific axis. The toe of the skierís boot will only release due to lateral forces whereas the heel of the boot will release in response to vertical forces. This leaves the skier vulnerable to injury in a situation where forces are in uncommon directions. Furthermore there are many situations in which a compromised ski stance may allow injury to occur due to forces low enough in magnitude that they do not trigger a traditional binding release. Experts in the field have concluded ďMost of the evidence suggests that the bindings considered in the published studies do not sufficiently address the multi directional release requirements for reducing the risk of lower limb, especially knee, injuries and that further technical developments and innovations are required [C.F. Finch 1998]. Electronic bindings have been patented which seek to alleviate injury risk by accounting for multidirectional forces in the boot by employing dynamometers linked to a solenoid release system [D. MacGregor, 1985]. Alpine Ski industry leader, Marker Skis, has also developed an electronic binding prototype that integrates the force on a skier foot over time to give a better metric for release [W. Knabel]. However, even with these improvements in safety, an electronic binding still has not been commercially sold.
The high injury rate in snow skiing is a limiting factor for many individuals considering the sport, and clearly the current binding manufacturers are very interested in improving the safety of their bindings so they could expand their market. However, the individuals designing the bindings have limited access to data about the forces and torques that a ski binding and skier can influence in the field. This is because almost all of the reviews of skiing injuries are put together from after the accident accounts of injuries and are therefore qualitative [A. Natri ET AL, 1999][C.F. Finch 1998]. Unlike sports such as running, where the natural motions of the sports can be performed in a laboratory environment and plotted using motion capture cameras [Corazza S, 2006], skiing must be performed in an outdoor environment in which the individual is not stationary. This has made quantitative data acquisition quite difficult.
With advances in MEMS technology itís imaginable that a recording system could be designed to monitor aspects of the skier such as ski orientation, forces in the boots/bindings, ski planar and angular acceleration, and ski speed/direction to name a few [9 Degrees of Freedom - MPU-9150 Breakout][H.J Luinge, 2005]. This would produce valuable quantitative data that could be analyzed to identify injury causing forces and help remodel current bindings. Eventually this system could be improved so that it would not only record this data in real-time, but could also process it in real-time which could allow for augmentation of electronic release systems. Specifically, if this system could determine the skiís orientation relative to one another, it could then identify when the skier is in a compromised position and lower the release threshold in the bindings to reflect this. This could prevent many injuries in which the force is strong enough to tear a skierís ACL due to a compromised position, but not strong enough to cause the binding to release at its preset threshold. Communication between the two bindings would also allow for simultaneous release, as one binding can check the status of the other and release if its partner is no longer attached.
Our design attempts to prototype a novel real-time recording system that would mount to the top of the skis behind the bindings and be inconspicuous to the skier. The system would then record data throughout the skierís runs down the mountain which could be later downloaded and analyzed. It is hoped that a dramatic increase in quantitative information about skiing will allow the creation of bindings that better identify appropriate release situations, saving skierís from unnecessary injuries.
For complete references please see PDS in documents section.
- Charles Rodenkirch - Team Leader
- Derek Pitts - Communicator
- Robert Carson - BSAC
- Gustavo Vargas - BWIG
- Hannah Meyer - BPAG
Advisor and Client
- Amit Nimunkar - Advisor
- Prof. Darryl G. Thelen - Client