Author: Robert Mooney, PhD student, Bioelectronics Research Cluster, National Centre for Biomedical Engineering Science, National University of Ireland Galway Technical evaluation of human performance is an essential part in the preparation of elite athletes. Novel methods of analysis, incorporating body-worn inertial sensors, have received much attention recently within both research and commercial communities – and rapid expansion of this marketplace has led to many new prototype designs. Practical and convenient methods of monitoring performance measures are especially important for sports such as swimming, where physiological and movement demands cannot be easily replicated in the lab. However, biomechanical analysis of swimming remains poorly explored due to complexities of kinematics measurement in water. In addition, currently available sensor-based systems lack the sophistication required to overtake alternative analysis tools and service the needs of elite athletes and coaches. Swim Ireland has teamed up with NUI Galway with a view to pioneering a new performance-analysis system that will provide whole-body, real-time feedback on swimming performance. This system will utilise innovative kinematic sensing technology coupled with novel feature extraction algorithms. Once developed, this will allow for improved analysis of stroke mechanics, race performance and energy expenditure, as well as providing for real-time feedback to both coach and swimmer, enabling more efficient, competitive and quantitative coaching. The research will require a collaborative effort to draw together many strands of expertise in the areas of electronic engineering, physiology and biomechanics. The development team is led by Prof Gearóid Ó’Laighin of the Department of Electrical & Electronic Engineering at NUI Galway. Technical evaluation of the movement patterns in swimming is currently overly reliant on the lengthy process of joint digitisation from video footage, making it difficult to evaluate a swimmers’ stroke and provide feedback in a timely manner. Recent advances in the miniaturisation of electronic wearable technologies, hydrophobic coatings enabling their use in water and the increasing availability of kinematic motion sensors facilitate a new approach to swimming coaching. [login type="readmore"] The team at NUI Galway will be capitalising on low-cost, high-performance Micro Electro Mechanical Systems (MEMs) technology. This technology shows incredible potential for transforming how technical analysis of human movement is conducted, with benefits in terms of accuracy, speed of feedback and depth of analysis. CHALLENGES There are a number of challenges that must be overcome. Sensors must be non-invasive, ergonomic and be appropriately designed to avoid negative drag effects, with housing and sensor placement critical features of the design. In turn, sensor placement will have a large effect on algorithm development. A sensor placed on the wrist, for example, will have a very different signal signature to a back-worn sensor, leading to differences in how algorithms are constructed for calculating key variables of interest. Combining and collating raw signal from multiple body segments presents another layer of intricacy to algorithm development. Real time, on-board data processing will require feature extraction algorithms that are ‘computational simple’, whilst still allowing for a depth of analysis that is of interest to the end user. To illustrate, determining a swimmers’ stroke count is a key performance related variable in competitive swimming and can be achieved using an automatic peak detection or zero-crossing algorithm. A trade-off between the size of the sensors and system functionality requires consideration for all aspects of the design phase. Essential components include accelerometers and gyroscopes for measuring linear acceleration and angular velocity respectively, which will provide for full six degrees of freedom when data is collected. However, other component parts including the microcontroller, on-board storage and communications modules further add to the complexity of the design when minimising size is at issue. Performance comparisons between different radio frequency (RF) communication bandwidths for wireless communication in a swimming pool have found that 2.4GHz is good for high data rate, but may be unsuitable for aquatic environments without design modifications unless operating in a burst mode, when air exposure is possible. Water in the near field of the antenna causes a reduction in the resonant frequency. RF suffers from high attenuation and whilst lower frequencies are more immune to water effects, the size of the antenna required would be a significant issue for the user and may not be a practical solution. One limitation of this is that the range of transmission is quite low. TRANSMISSION RANGE However, transmission range must extend to provide feedback to a coach standing on pool deck, whereas many current swimming performance analysis systems are focused on transmission directly back to a wrist-watch worn in the pool, targeted for the recreational swimmer. Alternative approaches may include optical or acoustic systems. Robert Mooney, PhD student at the National Centre for Biomedical Engineering Science and Kevin McGlade, NUIG scholarship student and member of the Swim Ireland Connacht Performance Centre based at NUIG[/caption]
An LED transmitter and photodiode receiver has been tested with limited success over very short communication ranges and will be effected by turbulent water owing to the swimmers’ movements. Acoustic systems also suffer a range of limitations, including propagation delay, path loss, multi-path fading, high bit error rate and limited bandwidth.
Energy consumption due to data processing, storage and transmission across multiple sensors presents another challenge. Lithium-ion based batteries are most prevalent in sensor based technology. However the functionality of such approaches does limit the size reductions necessary for swimming applications and they are potentially hazardous in aquatic environments. Current areas of research interest internationally are focused on alternative power generation methods, including super-capacitors and carbon-nanotube based energy stores. Another fascinating avenue of exploration lies in energy harvesting from ambient sources, which could extend battery life and reduce system complexity. APPLICATION Swim Ireland’s involvement serves to focus the development of a tool to directly impact on coaching performance, with Irish coaching expertise playing a key role in streamlining the range of potential applications from raw data signals into useable information for the coach on pool deck. The system will be tested on elite Irish swimmers to measure, record and track their technical improvements achieved with training. The value to the end user will ultimately determine the success of this technology. Peter Banks is performance director with Swim Ireland, the national governing body for aquatic sports in Ireland. He said that this type of technology was very exciting for Irish swimming to be involved with – the project gives coaches and swimmers an opportunity to learn more about how athletes perform in the training pool and helps the organisation to make more informed decisions around their training programmes. The preparation of elite athletes for competition is characterised by detailed and specific annual training plans designed to improve all aspects of athletic performance. Central to this preparation is the development of technical ability, a process led by experienced coaches, which is informed through quantifiable measurement and testing on a regular basis as a method to assess skill acquisition, development and progression. In timed-based sports, such as swimming, enormous effort on the part of coaches and sport scientists is invested in achieving improvements of fractions of seconds, which have been shown to be the difference between winning and losing on the international stage. The advent of new technologies has changed the perception of athletic achievement. A growing importance on devising new tools to assess self-improvement and optimise technical performance presents an exciting opportunity for Irish engineers to lead from the front. Robert Mooney is a PhD student within the Bioelectronics Research Cluster, National Centre for Biomedical Engineering Science, National University of Ireland Galway, under the supervision of Prof Gearóid Ó’Laighin. Funding for his PhD is made through the Irish Research Council Enterprise Partnership Scheme, in conjunction with Swim Ireland. Robert holds a BSc (first class honours) in Exercise & Sport Science. Prior to taking up the research position, Robert was the high performance co-ordinator for Swim Ireland. He currently works as a performance analyst as part of the Swim Ireland National Squads Programme.