An extensible implantable electrical lead comprising: a lead body having a proximal region and a distal region, the lead body formed of an extensible polymeric material that is extensible between a first length and a second length, the second length being greater than the first length; and a first plurality of electrical conductors each of the first plurality of electrical conductors comprising a first insulator layer, the first plurality of electrical conductors disposed within the lead body and extending between the proximal region and the distal region, the first plurality of electrical conductors are each electrically insulated by the corresponding first insulator layer and spaced apart from each other and form a side-by-side co-planar first sigmoidal pattern between the proximal region and the distal region and arranged in a first plane; and characterized by further comprising a second plurality of electrical conductors each comprising a second insulator layer, the second plurality of electrical conductors disposed within the lead body and extending between the proximal region and the distal region, the second plurality of electrical conductors are each electrically insulated by the corresponding second insulator layer and spaced apart from each other and form a side-by-side co-planar second sigmoidal pattern from the proximal region to the distal region and arranged in a second plane different from the first plane, wherein the first and second planes are parallel to each other, and a layer of the extensible polymeric material is disposed between the first plurality of electrical conductors and the second plurality of electrical conductors. a lead body having a proximal region and a distal region, the lead body formed of an extensible polymeric material that is extensible between a first length and a second length, the second length being greater than the first length; and a first plurality of electrical conductors each of the first plurality of electrical conductors comprising a first insulator layer, the first plurality of electrical conductors disposed within the lead body and extending between the proximal region and the distal region, the first plurality of electrical conductors are each electrically insulated by the corresponding first insulator layer and spaced apart from each other and form a side-by-side co-planar first sigmoidal pattern between the proximal region and the distal region and arranged in a first plane; and characterized by further comprising a second plurality of electrical conductors each comprising a second insulator layer, the second plurality of electrical conductors disposed within the lead body and extending between the proximal region and the distal region, the second plurality of electrical conductors are each electrically insulated by the corresponding second insulator layer and spaced apart from each other and form a side-by-side co-planar second sigmoidal pattern from the proximal region to the distal region and arranged in a second plane different from the first plane, wherein the first and second planes are parallel to each other, and a layer of the extensible polymeric material is disposed between the first plurality of electrical conductors and the second plurality of electrical conductors.