i e wherein the jaw retains the tip of the sole of the boot through the vamp portion there is no change in the linkage between the boot and its retention element if the retention element acts through a sole grip an adjustment in the opening of the wings of the jaw will certainly be necessary because the sole of the special boot will have been locally reduced to overcome this fig9 shows an alternative embodiment of the boot according to which the reduced zone of the boot which avoids the displacement of the sensor is formed by a groove 48 formed for example at mid height of the sole at the level of an angle this groove does not modify the exterior general contour of the sole so that such a boot is also compatible with the retention elements for gripping a sole for the boot shown in fig9 the sensor will preferably be a rod positioned at the level of the groove but of diameter smaller than its width the rod can preferably be flexible fig1 shows another alternative embodiment of the boot according to which the sole has in its lower portion a cutout 50 however in its upper portion the sole keeps a standardized contour and thus the boot remains compatible with traditional retention elements the construction which has just been described is not limiting and numerous alternatives are possible in particular for the preceding construction it is possible to reverse the direction in which the latches are.