I will talk about the existence of minimizers of the 3D neo-Hookean energy in the critical case, i.e., Sobolev exponent p=2. As shown by an example of Conti-De Lellis, already in the axisymmetric case, a phenomenon of concentration of energy can occur preventing the strong convergence of a minimizing sequence along with the equi-integrability of the cofactors of that sequence. The example suggests a specific relaxed energy. This allows to transform the lack of compactness problem into a regularity problem. I will provide bounds for this relaxed energy.