An exercise device includes a first elastic material portion having a first face and a second face disposed opposite the first face, a second elastic material portion having a third face and a fourth face disposed opposite the third face, and a plurality of joining regions, wherein the second face of the first elastic material portion attaches to the third face of the second elastic material portion at each joining region. Each joining region is capable of simultaneous multidimensional stretching when subjected to or released from an applied load. An assembly of integrally connected exercise devices includes a first exercise device integrally connected to a second exercise device, wherein a joining region is capable of separation into two smaller joining regions when the first exercise device and the second exercise device are separated.