To evaluate the effects of racing and training conditions on motion symmetry we set out to quantify hindlimb symmetry using an objective inertial sensor-based system in a cohort of in-training Standardbred racehorses during high-speed trotting and to assess the influence of speed, line taken (straight vs. bend) and direction of travel (clockwise vs. anticlockwise).


Eight Standardbred racehorses in full training were instrumented with a GPS-enhanced inertial sensor located at the tuber sacrale and trotted around an oval racetrack at a range of speeds and in both directions. Symmetry index (SI), MinDiff, MaxDiff, vector sum (VS) and range of motion (ROM) were quantified for the hindlimbs for each stride using vertical displacement data derived from the inertial output.


A total of 9108 strides were collected on the track. Overall, all horses displayed a right hindlimb asymmetry or ‘lameness’. Horses were more asymmetrical when trotting around bends compared with on straights. The main factor influencing asymmetry was trotting around a clockwise bend. Speed had a small but significant influence on asymmetry that varied between measures.


The inertial sensor system was suitable for collecting on-track, high-speed locomotion data. The magnitude of asymmetry was dependent on direction, possibly indicating subclinical lameness or laterality in these horses.

Practical significance

The inertial sensor system is practical for on-track objective high-speed lameness evaluation. Further studies with larger numbers of objectively sound and lame Standardbred horses are needed to determine the effect of lameness on high-speed trotting. The influence of factors such as training regimes and racing equipment should also be evaluated.

Ethical animal research

All procedures were performed with approval of the Royal Veterinary College Ethics Committee. The study was carried out in accordance with local regulations and in collaboration with the Swiss National Stud and Vetsuisse Bern. Informed consent was obtained from the owners of all horses used. Approval no. 2012/P358. Sources of funding: None. Competing interests: None.