July 3, 2008 The development of Fusion Motion Capture (FMC) by Massey University PhD student Matthew Brodie has some broad implications for sport. Though initially focussed on enabling biomechanical analysis of ski racing, Brodie’s FMC system is worn by the athlete and promises much for the understanding of many sports. Unlike traditional biomechanical analysis which uses video cameras, FMC, using a range of inertial sensors, pressure pads and GPS attached to the athlete’s limbs, helmet and feet to generate raw data from the athlete’s movement. The numbers are then crunched by a computer to produce accurate estimates of the position, velocity and acceleration of the limb segments.

Brodie developed FMC to measure a complete ski run and the gear he put together enables us to measure for the first time how a human performs complex tasks in the everyday world. The subject is free to travel unconstrained for any length of time while fusion motion capture collects their movement data.

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Biomechanical analysis of most sports is routine at the elite level these days, and is usually done using video but there have been some sports which are very difficult to do this with because the sportspeople travel over longer distances or difficult terrain. Skiing in particular brings an enormous challenge to measuring the real-time biomechanics of athletes, because, as Brodie explains, “there just aren’t enough cameras available to do things in the traditional way.” While video analysis requires several weeks to measure only a few movements, FMC is able to collect and analyze several hundred turns in a single day.

The development in FMC for real time sports monitoring in the hostile and difficult alpine environment is hence very relevant for cross country runners, sailors, rowers, cyclists, and a host of other out-and-about sports. The data is stored on the athlete and analysis is performed later.

Brodie’s thesis which will be finished later this year, is titled 'The Optimisation of Athlete Movement in Alpine Ski Racing'. His Fusion Motion Capture (FMC) technology was developed to capture the 3D kinetics and kinematics of alpine ski racing using inertial sensors, pressure pads and GPS.

The system uses sensors attached to the athlete’s limbs, helmet and feet to generate raw data from the athlete’s movement. The numbers are then crunched with the aid of a computer to reproduce accurate estimates of the position, velocity and acceleration of the athlete’s limb segments.

FMC is a general term to describe motion capture when several different streams of data are fused to measure athlete motion. Brodie combines inertial measurement units (IMU), global positioning system (GPS), pressure sensitive insoles, video and theodolite measurements to obtain his raw data though in the future, it’s possible that other data might be used from gyroscopes or magnetometers. GPS data is fused with local acceleration data to track the global trajectory of the athlete.

“With FMC, it is possible to capture motion and dynamics of alpine ski racing throughout the ski run while maintaining high resolution. This is the first time full body motion of an athlete skiing an entire course can be captured with results returned as soon as the run is completed”, says Brodie.

Brodie adds, “FMC-enabled biomechanical analysis which provides insights into how technique, race strategy and equipment changes can increase the athlete’s speed. It is now possible to measure how ski friction, wind drag, gravity and ground reaction forces affect performance and see how variability in technique is beneficial to race time.”

As more accurate dual frequency GPS systems become less expensive this type of system will become more accurate and affordable – Brodie’s current skier-wearable-kit cost around US$80,000, but Brodie suggests that once thoroughly developed, it will cost a faction of that amount, “particularly if it follows the same path as the Wii remote, which essentially uses the same technology.”

The abundant data available via FMC required the creation of new tools for measuring alpine ski racing technique, such as colour-coded force vector analysis. New parameters, such as effective inclination and ground reaction force power, are independent of the stylistic constraints often imposed by the coach or athlete.

There’s also a full article on Fusion Motion Capture (FMC) featured in Wiley-Blackwell’s journal, Sports Technology, this month. In the paper, two ski runs from the same skiier were compared. Although the difference between the two run times was only 0.14 s or 1%, FMC and force vector analysis were able to pick up the subtle changes in technique between the two runs and chat with Brodie indicates the vast knowledge he can glean from his analysis.

It is believed the analyses will provide useful design parameters to ski equipment engineers and will allow athlete feedback through augmented reality animations about variables, including limb dynamics, centre of mass (CoM) trajectory, CoM velocity, and external forces.

In-depth analysis of the changes in net joint torques with changes in athlete posture may be useful for coaching athlete specific technique changes to improve performance and reduce injury potential. In addition, it is possible to extract key performance indicators about the athlete's physical and physiological limits, such as the mean coefficient of wind drag and the maximum inclination angle while turning, which may be used to optimise race strategies. There are tentative plans to use an improved version of a similar motion capture system to analyse forerunners on the FIS world cup race circuit with a view to reducing knee anterior cruciate ligament (ACL) injuries.

Future health applications for FMC might include activity monitoring, postural balance analysis in fall prevention programs, and gait analysis during everyday tasks. FMC also promises much as in the entertainment side of things (as a games interface), motion capture for the film and games industry and to provide a visual biomechanical analysis of an athlete playing any sport to enhance the experience of the television audience.

‘’’’’’’’’’ Sports Technology

Reproduced from a Brodie, M. A., Walmsley, A., & Page, W. (2008). Fusion motion capture: a prototype system using inertial measurement units and GPS for the biomechanical analysis of ski racing. Journal of Sports Technology, 1(1), 17-28.) with permission from Wiley-Blackwell.


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