This paper presents the characterization of the mechanical properties, of the ability to crystallize thermally or under strain, and of the Elastically Active Chains (EAC) network of Natural Rubber elastomer, whose EAC average density and length distribution were modified by thermo-oxidative ageing. EAC length distribution is not a critical parameter for λ break in elastomers which do not crystallize (as far as the quantity of free and dangling chains stays negligible, which is the case in this study). However, it becomes important in crystallizable materials, since it controls the chains quantity which can be stretched enough to crystallize. When this quantity is large enough, the material can be stretched up to λ c , and the crystallization process will enable to increase both λ break and σ break . Conversely when it is too low, λ break is seemingly mainly governed by the average EAC density and a power law then links both quantities. © 2019 Elsevier Ltd