Quantitative assessment of gait alterations and variability in sulky-driven Standardbred trotters after a standardised exercise test

Background Assessment of equine metabolic and locomotory responses to quantified levels of physical exercise is needed to support the creation of tailored protocols for optimal training adaptation. The locomotory response to exercise in horses is not fully understood. Objectives To investigate the effect of a standardised exercise test (SET) on upper-body and limb kinematics and stride-to-stride variability in Standardbred Warmblood trotters.Study Design Experimental repeated-measures field study. Methods Thirteen Standardbred trotters, equipped with nine inertial measurement units (IMUs), performed an incremental SET on an oval track. Heart rate and lactate data were collected to identify internal workload. Two 30-s segments of jog on the straight (at the beginning and at the end of the SET) were used for statistical analysis of the effect of the SET on locomotion parameters. Results Upper-body kinematics revealed a decrease in head and withers range of motion (ROM; -12.3 mm; p = 0.04 and -8.5 mm; p = 0.01, respectively). Front limb sagittal ROM (16.1 degrees; p = 0.001) increased explained by increased maximal protraction and retraction (6.9 degrees, p = 0.002 and 9.1 degrees, p = 0.002, respectively). Stride-to-stride variability (i.e., coefficient of variation) was reduced for stride duration (-0.7%; p = 0.01), front limb sagittal ROM (-7.3%; p = 0.04), front limb maximal protraction (-6.9%; p = 0.01) and maximal retraction (-7.4%; p = 0.03). No effects were found on sagittal hindlimb angles and none of the absolute asymmetry parameters changed (p > 0.05). Main Limitations Horses were of different ages and training statuses, and full orthopaedic examinations were not performed. Conclusions Several kinematic parameters were affected by the SET. Head and withers ROM were reduced, while front limb sagittal ROM increased. Stride-to-stride variability showed a decrease. The results indicate that exercise in Standardbred trotters produces both a metabolic and locomotory response. Additionally, these findings highlight the efficacy of IMUs as a non-invasive tool for detecting exercise-induced changes in limb and upper-body kinematics.