Front crawl swimming is a cyclic activity in which swimmers alternate arm and leg movements to create propulsive forces while the body rotates about its longitudinal axis. This motion is referred to as the body roll of the trunk. lt has been suggested that breathing increases body rotation and potentially disrupts the symmetry of the stroke (Psycharakis & Sanders 2008). Inertial sensors are an emerging and accessible technology for quantifying movement in aquatic environments (Bachlin & Troster 2011). Previous studies have suggested that accelerometer derived data for stroke parameters can be as good as or better than data derived from video (Davey, Anderson & James 2008). This study quantified the effect of breathing on hip roll angle using a body-fixed tri-axial accelerometer. Recent studies have shown that velocity and breathing are important factors affecting the degree of body roll during front crawl swimming. These studies have shown that as velocity increases, body roll of the trunk as a single segment decreases (Yanai 2003; Castro, Vilas-Boas & Guimaraes 2005) and that body roll, when the trunk is measured as a single segment (Payton, Bartlett, Baltzopolous & Coombs 1999) and when it is measured separately as hip and shoulder roll (Psycharakis & Sanders 2008), is greater when breathing than when not breathing. A further study by Psycharakis and McCabe (2011) suggested that whilst swimmers roll their shoulders and hips significantly more to the breathing side when breathing than when not breathing, the total body roll angle was not significantly different between breathing and non-breathing trials. The authors suggested that a compensatory strategy exists on non-breathing stroke cycles to maintain a similar total body roll angle to the breathing cycles. One might assume that other cyclic locomotor activities such as walking, running and cycling would display symmetric movement patterns. However, research has shown that a degree of bilateral asymmetry is present in the propulsive forces of running and cycling (Sadeghi, Allard, Prince & La belle 2000; Carpes et al. 2011). In front crawl, a unilateral breathing pattern is inherently asymmetric, as the swimmer will rotate more to the breathing side. In theory, a bilateral breathing pattern should prevent bilateral asymmetry; however, no previous studies have quantified the degree of body roll angle in bilateral and unilateral breathing conditions together. Therefore, the purpose of this study was to determine the effect of breathing on body roll angle, specifically hip roll, in elite competitive front crawl swimmers. More specifically, the extent to which hip roll angle and hip roll asymmetry differed between unilateral and bilateral breathing conditions was investigated.
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