Swimming is a very well-known activity which has applications in health, education, and recreation. Anyone, from children to the physically disabled and even the elderly can participate in swimming, often with positive effects on their health. Quantitatively measuring data can give us more valuable information about a swimmers technique [1]. 

Swimming requires good body position and the cyclic repetition of the limbs and trunk performed in unison to achieve proper technique. One of the more important parameters when swimming is body roll, especially in freestyle technique, defined as the swimmers angle around their long axis [2]. The yaw angle is of less importance and should maintain consistently small changes in amplitude to avoid cross-over (over expenditure of energy). The article uses a 9 DOF IMU to measure the orientation and accelerations of the swimmers COM in freestyle swimming. The electrical components and battery of the IMU are housed within a waterproof casing and mounted directly on the swimmers COM [3].

[1] Bence M. et al, Swimming, UMB v Banskej Bystrici, ISBN: 80-8083-151-6, 2005. (in Slovak)
[2] Ethier, C.Ross et al, Introductory Biomechanics: From Cells to Organisms, University of Toronto, Cambridge University Press, pp. 332-471, 2007.
[3] Šoltés L. et al, Obtaining Kinematic Gait Parameters from IMU sensors, in Proceedings TEAM 2012, p.51-53, ISSN: 1847-9065 Volume IV no.1 , Croatia, 2012.