The objective of the Sequisol project is to characterize the effects of equestrian ground/track surfaces on the equine locomotor system. This project is based on an experimental protocol combining several biomechanical measurement tools, simultaneously used and that allow to quantify, among others, the 3D-ground reaction force (under the horse's forefoot), and the acceleration and vibrations supported by the foot. This protocol has been applied on harness trotters, at 35 km/h in straight line. This article presents: 1. the comparison (on 3 horses) between two training tracks, respectively in "machefer" (clinker) and in soil, and a hard pathway: the maximal deceleration at impact appears significantly higher, and vibrations are increased on the hard pathway; the maximal vertical force also tends to be higher; 2. the preliminary results of the tests performed since novembre 2006 in the context of the Sequisol project (10 tracks tested on 4 different sites): this comparison demonstrates the shock-absorbing properties, during the braking phase, of the all-weather waxed tracks, and generally speaking, the strong influence of maintenance conditions of the surfaces on the biomechanical results.