Authors: Rowlands, D. and James, D.

Procedia Engineering 13 (2011) 464-469.

Video analysis has long been consid­ered the most practical and relevant method for monitoring athlete perfor­mance; however, the recent trend of utilizing multi-functional sensors to monitor performance has increased dramatically due to the decrease in size and the overall practicality of these sensors to monitor sport per­formance. Despite the advantages of multi-functional sensors, the cost and complexity of these devices and their associated software prevents use with­in the broader sporting community. Therefore, it is also necessary to con­sider less expensive, more accessible monitoring devices that can benefit a wider audience (like our developing athletes, for example). One particular device that is highly accessible and cost-efficient is the smartphone. In fact, the smartphone contains many of the functions of expensive sensor and data acquisition units, including: GPS, triaxial accelerometers, triaxial gyroscopes, data logging, and wireless streaming.

This article outlines the methodology for successfully extracting three di­mensional accelerometer data from a smartphone, both wired and wirelessly. In the provided example, the research­ers demonstrate this technique using an iPhone 4 during a jogging task. One concern that is immediately evi­dent is the limited measurement range of the iPhone’s accelerometers at ±2g (g = -9.81m/s2). Even in a low inten­sity task such as jogging, the acceler­ometer’s range was maxed out during most cycles. In higher intensity ap­plications, such as running, this could become an issue if attempting to iden­tify a high acceleration event; once the acceleration exceeds ±2g a flat wave will replace the acceleration spike, resulting in imprecise and inaccurate measurements. On the other hand, for smooth tasks such as speed skating or rowing the range of accelerations is much smaller. In these applications, the smartphone would be more suit­able as a measurement device.

Smartphones offer numerous advan­tages over other measurement devices, with the most important being acces­sibility. However, the smartphone is not the best measurement tool for all sports, as they have a limited mea­surement range, are bulky, and the software interface is less user friendly than other commercially developed systems. For those who are willing to invest some extra time to understand the process of extracting data from a smartphone, the cost savings and po­tential for widespread application in your sport make this a desirable alter­native to proprietary multi-functional sensors. Of course, it is important to properly secure and protect your phone before using it as a measurement tool; after all, you are risking more than just a sensor.