Currently, the most accurate and noninvasive method used to assess energy expenditure (EE) in sport horses is based on heart rate (HR) monitoring. However, EE assessment using inertial platforms has been lately discussed in human sports medicine. The objective of this study was to evaluate whether inertial platforms would be useful tools to assess EE in horses. Six show-jumping and riding school horses (Thoroughbred and warmblood) were equipped with a HR monitoring system and a wireless inertial platform. Acceleration, HR, and speed were measured during the exercise protocol that included walk, trot, canter, and a sequence of four jumps. Stride maximum and minimum acceleration, and acceleration amplitude and root mean squares (RMSs) were determined. Energy expenditure and oxygen uptake (VO2) were calculated using HR and speed, respectively. Bivariate correlations (nonparametric Spearman's ρ correlation) between EE, VO2, and acceleration variables were tested. Spearman's ρ correlation was positive between both EE and VO2, and maximum acceleration, acceleration amplitude, and RMS and negative for minimum acceleration. Acceleration variables of vertical and lateral movement were generally better correlated with EE and VO2 (P < .001) than those of forward movement (P < .01). The results of this innovative approach reveal that the determination of EE in horses could be assessed using inertial platforms. Moreover, vertical and lateral movements appear to influence more EE than forward movement.