Studies assessing the effect of the rider’s sex on racehorse performance and physiology during training have not been reported, mostly due to the paucity of available data for female participants within the sport. Here, using a validated system (the ‘Equimetre’™) that records all parameters simultaneously, we objectively report the effect of rider’s sex on racehorse cardiovascular (heart rate, heart rate recovery) and biomechanical parameters (stride length and frequency) at various exercise intensities (slow canter to hard gallop). 530 Thoroughbreds, varying in age (2-7 years old) and sex (including geldings), from one racing yard in Australia, completed a total of 3,568 exercise sessions, monitored by a single trainer, on varying track surfaces (sand, turf, or fibre). 103 different work riders (male, n=66; female, n=37) of which n=43 were current or past registered professional jockeys, were used. Data were analysed using analysis of variation (ANOVA) or mixed-effect models, as appropriate. Sex of the rider did not influence racehorse speed (P=0.06) nor stride length (P=0.42) at any training intensity. Heart rate and peak heart rate increased with training intensity (P<.001), with no difference according to sex of rider (P=0.73). Heart rate recovery after exercise appeared influenced by rider sex, but only when the usual training intensity on each surface was reversed, suggesting an interaction between racehorse anticipation of exercise and rider sex. Male jockeys had slightly higher strike rate in races in Australia, but not the UK. This study demonstrates no overt effect of rider sex on racehorse performance and physiology.