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Wearable Technologies for Performance Assessment

Sports Medicine Australia Symposium We recently hosted a symposium at the Sports Medicine Australia Annual Conference in 2008 in Brisbane on technology in sport.
The testing and monitoring of elite athletes in their natural training environment is a relatively new area of development that has been facilitated by advancements in microelectronics and other micro technologies. Whilst it is a logical progression to take laboratory equipment and miniaturize it for the training and competition environment, it introduces a number of considerations and complexities that need to be addressed. In this symposium examples of miniturised technology using inertial sensors are applied to a range of sporting applications yielding field based results analogous to those achieved in the laboratory but under typical training and sometimes performance conditions. The symposium features papers from a range of sporting disciplines to show what is possible, the challenges and limitations of the technology as well as helping to assist the development of the sport. Authors will be invited to form a panel for free flowing discussion on adoption of the technology into other sports of interest to attendees and to elaborate on additional sporting applications they have been engaged in where there is time.

Paper 1: Microtechnology for measuring intra-stroke arm and leg timing in swimming.
Paper 2: Wearable Sensors for the Monitoring of Bowling Action in Cricket
Paper 3: Comparison of Center of Mass and Chest Based Inertial Sensors in the Soccer Throw-in.
Paper 4: Accelerometry of underwater walking

Microtechnology for measuring intra-stroke arm and leg timing in swimming.

B. Burkett1*, D. James2, D. Thiel2, N. Davey2
1University of the Sunshine Coast
2Griffith University

Introduction: The measurement of technique for an athlete has traditionally been performed in the laboratory where the required instrumentation is available and environmental conditions can be easily controlled. In this environment, dynamic characteristics of athletes are assessed using treadmills, rowing and cycling machines and even flumes and tethers for swimmers. In general these machines allow for the monitoring of athletes using instrumentation that cannot be used in the training environment, but instead requires the athlete to remain quasi-static, thus enabling a constant field of view for optical devices and relatively constant proximity for tethered electronic sensors, breath gas analysis etc. The use of accelerometers to measure activity levels for sporting, health and gait analysis is emerging as a popular method of biomechanical quantification of health and sporting activity. Detailed analyses of the fine structure of movements reveal critical performance characteristics, which potentially can shave milliseconds from lap times. The objective of this research was to measure the intra-stroke movement patterns for elite swimmers, specifically the timing of arm-stroke and leg-kick and provide new information to QAS swimming coaches on as the athletes are freely swimming in training and/or race simulation conditions.

Methodology: The reliability and validity of the micro-technology was quantified via graduated comparative analysis of the inertial sensor outputs relative to a recognized benchmark. Using a National Sports Science Quality Assurance motion analysis laboratory and Qualisys® six camera 500Hz three dimensional motion analysis system a simple, single plane movement task of flexion/extension of the knee joint was measured and compared for validity and reliability. The calibrated inertial sensors were placed on the hand, head, sacrum, and ankle of the swimmer prior to entering the water. The data collection was synchronised on the sensors via a radio frequency and the swimmers completed 100 m freestyle swimming.

Results and conclusions: This new monitoring system provides currently unknown feedback on the intra-stroke timing mechanics for swimmers, which is a fundamental factor in enhancing performance. Specifically the timing of the pull and recovery phase in relationship to the kick are identified in free swimming. From this benchmark variations in the pattern of intra-stroke timing due to fatigue or change in velocity can be identified. This critical and real-time information can led in substantial changes in training techniques of the coaches and athletes.

Wearable Sensors for the Monitoring of Bowling Action in Cricket

A. Wixted1*, D. James1,2, A. Busch1 & M. Portus3
1Centre for Wireless Monitoring and Applications, Griffith University
2Centre of Excellence for Applied Sport Science Research, Queensland Academy of Sport
3Centre of Excellence, Cricket Australia

Introduction: In the laboratory environment biomechanical characteristics of cricket fast bowlers are assessed using a variety of analysis systems such as retro-reflective motion analysis systems (e.g. VICON). In general these systems allow for detailed and sophisticated analysis of human movement but are limited to the contrived laboratory environment. Previous studies into bowling actions have typically relied upon frame by frame high speed match video analysis or 3 dimensional motion analysis obtained in a laboratory setting. It is generally considered that laboratory analyses provide a more detailed and accurate analysis of bowling actions including “suspect action” but do not provide a “real world” analysis environment.

Methodology and Results: Using previously developed wearable technology it is possible to measure arm action at a number of points on the bowling arm. The technology is based on inertial sensors and measures the arms changes in motion hundreds of times a second. These sensors respond to minute changes in inertia in linear and radial directions. These are known as accelerometers and rate gyroscopes, respectively. When combined with absolute positioning technologies such as magnetometers and even GPS (Global Positioning System), laboratory equivalent performance analysis can be obtained.. By comparing the movement of different limb segments it is possible to devolve a detailed picture of arm action.. Case study results from a sub elite bowler show clear differences between throwing and bowling action with elbow abduction and extension being clearly evident signatures in the data Conclusions: The sensors have been shown to be able to classify arm action with comparable accuracy to existing lab based methods. It is hoped that with more complete validation this technology can be used as a training tool to aid in the correction of bowling action to prevent injury, improve performance and correct suspect action.

Comparison of Center of Mass and Chest Based Inertial Sensors in the Soccer Throw-in.

D. Rowlands1 & J. Neville1*
1Centre for Wireless Monitoring and Applications, Griffith University

Introduction: Soccer is one of the most popular team sports played in the world. The throw-in is a method to restart play after the ball has left the playing area and occurs many times in a game. more info...

Accelerometry of underwater walking

Y. Ohgi1*, K. Kaneda1* & C. Tanaka2
1Graduate School of Media and Governance, Keio University
2Division of Integrated Sciences, J. F. Oberlin University

Introduction: Underwater walking ensures safe and moderate exercise for all levels of people including the elderly, obese, injured and some cases of the physically handicapped. On one hand, land walking has its evaluation method for both the intensity and the energy expenditure by using an accelerometer. On the other hand, the practical assessment of underwater walking is still an unexplored field. Our final goal is to develop an underwater pedometer by using an accelerometer with wireless function. The purpose of this study was to analyze quantitatively the acceleration signal patterns which were obtained during underwater walking. Method: Firstly, the authors carried out an observation of normal underwater walking. Fifty Japanese males (n=29, age: 27-73) and females (n=21, age: 33-70) participated in the experiment. They conducted free walking at stepwise speeds from 25m/min to 40m/min. An embedded tiny accelerometer was attached onto the occipital region of the subjects and recorded three dimensional acceleration at 100Hz. In the subsequent experiment, the authors attached the same accelerometers onto the three locales of the subjects’ body, such as the occipital region, low back and front ASIS. Results and Discussion: Experimental results show that the subjects’ experience of the underwater walking strongly affects the vertical acceleration. Then it causes estimation error for the energy expenditure and the number of steps. The attached accelerometer onto the subjects’ occipital region has its inclination angle to the gravity. There were much variety of this angle and it makes effect to the acceleration components of both the horizontal and vertical axis. Eliminating this acceleration component from the measured acceleration, the authors could obtain a polynomial estimation equation for the energy expenditure by using acceleration and the walking speed of the walker. Then we got a good estimation for the energy expenditure with this equation. According to the second experimental result, location of the attached accelerometer was very important for the theoretical and experimental estimation of its acceleration components. In addition, the accelerometers attached on the low back of the subject were affected by the turbulent flow behind the walker which might be an unpredictable acceleration signal. Conclusion: The authors recommend that the occipital region, namely the rear head of the walker should be a better acceleration fixing point and its acceleration patterns could predict the energy expenditure during underwater walking.

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