I have no trouble mobilising spinal joints through layers of soft tissues. The first proceedure that I would consider would be to restore normal lumbar facet mobility by reducing protective tone around them, this is best achieved with longest term effect with continuous mobilisation to fact joints. Further attentions to adjacent larger muscle ( MET or trigger point release ) may be warranted under some cirtcumstances , though I rarely find this necessary. By reducing focal irritants to nerve roots in this way , there will be restoration of normal patterns of recruitment to the lower limbs and the "muscle imbalances " will dissapear.