"In horses, and most other mammalian quadrupeds, 57% of the vertical impulse is applied through the thoracic limbs, and only 43% through the hind limbs.”  (H. W. Merkens, H. C. Schamhardt,G. J. van Osch, A. J. van den Bogert, 1993).

Chazot is learning here to develop the forelegs’ propulsive activity at the trot departure. This is done teaching the horse to control accelerations of gravity through his vertebral column and therefore regulating the weight on the forelegs. The riding technique allowing such education is about matching the biomechanical properties of the rider’s vertebral column with the biomechanical properties of the horse’s vertebral column. The reins are long and there is no weight on the bit. Once in a while the rider reminds the horse to do not push on the bit. 

This technique differs widely from the usual driving the horse onto the bit. Driving the horse onto the bit is a primitive technique that is based on antiquated knowledge of the equine biomechanics. Rushing the horse on the forehand and/or lowering the neck increases the weight on the forelegs. The technique hampers the horse’s ability to move efficiently and soundly.