Kiely, M, Warrington, GD, McGoldrick, A, Pugh, J, and Cullen, S. Physiological demands of professional flat and jump horse racing. J Strength Cond Res 34(8): 2173-2177, 2020-No information is currently available on the effect of race distance on the physiological demands of jockeys. This study aimed to quantify the respective demands of short and long flat and jump race distances. Twenty professional jockeys (10 flat and 10 jump) participated in the study. The subjects initially performed a graded incremental exercise test to volitional exhaustion on a treadmill to determine the peak heart rate (HR) and blood lactate concentrations. Two competitive races (short and long) were then monitored on 2 separate occasions for each jockey type to obtain hydration, HR, blood lactate concentration, and rating of perceived exertion data. Mean distances for the 4 races were: 1,247.2 ± 184.7 m (short flat race), 2,313.4 ± 142.2 m (long flat race), 3,480.2 ± 355.3 m (short jump race), and 4,546.4 ± 194.3 m (long jump race). The mean HR for the long flat race was 151 ± 19 b·min (79 ± 11% of HRpeak), which was significantly lower than all other race distances (p = 0.000, effect size [ES] = 0.469). A longer jump race resulted in a significantly higher reported rate of perceived exertion (RPE) (14 ± 2.8) than the short jump race (11.0 ± 1.5) (p = 0.009, ES = 0.271), whereas no significant difference was revealed between peak HR responses or blood lactate concentrations when comparing other race distances (p < 0.05). The finding of this study supports previous limited research, which suggests that horse racing is a high-intensity sport, whereas RPE and mean HR fluctuate according to the race distance.