Existing models still fail in correctly describing the relationship between the strain induced crystallinity (SIC) occurring in elastomer such as Natural or Synthetic Poly-Isoprene (PI) Rubber and their mechanical response. Preliminary experiments carried out at the D2AM beamline (proposal A021-900, main proposer G. Coativy, report 20201186) showed the determining role of the loading history on SIC since it enables to obtain, for a same crystallinity and stretching level, a very different mechanical response. This is likely related to the different stretching states of the amorphous chains which connect the crystallites, at the time these ones are nucleated and grow. Our objective is therefore to perform original in situ SAXS/WAXS experiments using PI elastomers, crosslinked so that their chains between crosslinks have initially different lengths and stretching levels ; these materials will be submitted to different loading paths combining relaxation and fast stretching steps.