## Introduction

Unilateral lameness is characterised by asymmetry during the left and right stance phases of a stride. Many methods have been developed to enable objective analysis of kinematic asymmetry (Buchner *et al*. 1996; Peham *et al*. 1996, 1999; Uhlir *et al*. 1997; Keegan *et al*. 2001; Kramer *et al*. 2004). Quantitative analysis of lameness usually involves the calculation of symmetry ratios. A symmetry ratio refers to the calculation of a ratio aimed at describing parameter asymmetry between the left and right phases of a stride. Kinematic studies have calculated symmetry ratios to enable asymmetry to be quantified numerically (Peham *et al*. 1996; Pourcelot *et al*. 1997; Keegan *et al*. 2001, 2004; Audigie *et al*. 2002; Church *et al*. 2009).

Trotting is a symmetrical gait (Hildebrand 1965) with each of the diagonal pairs being dynamically coupled. Most methods of calculating kinematic symmetry ratios produce a ratio of 1 (100% symmetry) if the parameter under investigation is symmetrical (Pourcelot *et al*. 1997; Audigie *et al*. 2002; Church *et al*. 2009). If the ratio is ‘non-directional’ then an increase in asymmetry corresponds to a reduction in ratio towards zero regardless of the side of the lameness. Three published methods used for analysis of kinematic symmetry utilise different parameters or use a slightly different approach while maintaining similar overall principles (i.e. quantifying left/right symmetry). To date, no comparison between these methods has been performed; however, many studies utilise only one of the methods to define changes in symmetry during investigations, therefore limiting comparisons between studies.

The aim of this study was to quantify differences between 3 published methods of sensor-based kinematic symmetry ratio calculations. This was approached with 3 objectives: 1) Compare 3 methods of ratio calculation to assess the use of tuber coxae against *os sacrum* displacement data for calculation of symmetry ratios; 2) determine the effects of circular trotting on symmetry ratios and 3) investigate the use of whole trials in place of individual stride calculations.