Summary Reasons for performing study: Inadequate track surfaces are believed to be a risk factor in the occurrence of musculoskeletal injuries, but quantification of the shocks and vibrations provoked by hoof impact on different ground surfaces (including new synthetic tracks) has been insufficiently documented in trotters under high-speed training conditions. Objectives: To test the reliability and sensitivity of an accelerometric device to discriminate between the biomechanical effects of 2 different tracks at high speed. Methods: Three French Trotters were used and their right front hooves were equipped with one triaxial accelerometer. Two different track surfaces (crushed sand track: S and all-weather waxed track: W) were tested when horses were trotting in a straight line. For each session of measurements, trials were repeated 3 times in a Latin square design. The speed of the runs was set at 10 m/s, controlled by the driver and recorded synchronously. Sample rate was set at 6 kHz. Acceleration of the hoof (resultant vector and 3D components), power spectral density at impact and variability (between strides, trials, sessions and horses) were analysed. Statistical differences were tested using a GLM procedure (SAS). Least square mean differences were used for comparisons between tracks (P<0.05). Results: Results showed that the deceleration of the hoof (magnitude of the resultant vector) was statistically different between the 2 tracks with an attenuation of the shock of about 50% on the all-weather waxed track. Magnitude of the power spectral density was reduced at higher frequencies on W. Conclusions and clinical relevance: These preliminary results demonstrate the sensitivity of the tool to discriminate between the different behaviours of the hoof on the different track surfaces at high speed. Deceleration and vibration of the hoof at impact were reduced on W compared to S, suggesting a better shock-absorbing quality of this track. Introduction Inadequate racetrack surfaces are believed to be a risk factor in the occurrence of musculoskeletal injuries at high speed. However, the actual effects of track surface characteristics on biomechanical EQUINE VETERINARY JOURNAL Equine vet. J. (2009) 41 (3) 247-251 doi: 10.2746/042516409X394463 247 Effects of a synthetic all-weather waxed track versus a crushed sand track on 3D acceleration of the front hoof in three horses trotting at high speed H. CHATEAU*, D. ROBIN, S. FALALA, P. POURCELOT, J.-P. VALETTE, B. RAVARY, J.-M. DENOIX and N. CREVIER-DENOIX UMR INRA-ENVA 957 de Biomécanique et Pathologie Locomotrice du Cheval, Ecole Nationale Vétérinaire dʼAlfort, 7, avenue du Général de Gaulle - 94704 Maisons-Alfort, France. Keywords: horse; accelerometer; high speed; track; trot parameters are insufficiently documented, especially under high- speed training conditions. Given the increasing interest in synthetic track surfaces in the horse industry, an objective assessment of their effects on the equine distal limb is needed for a better understanding of their possible advantages and drawbacks for the orthopaedic health of the horse. In this context, a comprehensive study has been set up to analyse the effects of different track surfaces on acceleration of the hoof, ground reaction forces, tendon load, and kinematics of the limb and trunk. The results reported here focus on the accelerometric data of this study. The phase of rapid loading following initial contact of the hoof with the surface is generally accepted to be important for the orthopaedic health of the horse (Johnston and Back 2006). Based on studies in other species (Radin et al. 1973; Serink et al. 1977), chronic exposure to impact has been linked to degeneration of articular cartilage and subchondral bone. The movements of the hoof at impact can be described as a series of peak decelerations causing shockwaves that are transmitted through the hoof capsule and bony tissues of the distal limb (Gustas et al. 2006a). Shock and vibration during hoof impact on different ground surfaces and at various gaits have already been measured at slow trot (Barrey et al. 1991; Gustas et al. 2001, 2004, 2006a), fast trot (Gustas et al. 2006b) and gallop (Ratzlaff et al. 2005) but differences between track surfaces at high-speed trot have not been investigated so far. Barrey et al. (1991) studied hoof impact at slow trot (4 m/s) on a number of different surfaces. They found that impact intensity was related to density and composition of the track. More recently, Gustas et al. (2001) have shown, using triaxial accelerometers mounted on the third metacarpal bone and the hoof, that the time lapse of the horizontal retardation of the hoof is also an important factor in the attenuation of the impact. This makes parameters that affect horizontal braking (such as the coefficient of friction between hoof and ground surfaces) important to the orthopaedic health of the horse. At different speeds, Gustas et al. (2006b) documented that the absolute length of the hoof- braking period is 30–50 ms and is independent of speed. The total period of concussion is approximately the period of muscle latency, which implies that the events at concussion cannot be modulated by muscle contraction. At slow trot, Gustas et al. (2006a) showed that the initial vertical deceleration of the hoof was higher on a sandpaper surface compared to a 1 cm layer of sand. Those *Author to whom correspondence should be addressed. [Paper received for publication 10.06.08; Accepted 14.10.08]