US Patent 8979716 Portable exercise equipment

A portable exercise device includes an anchor portion, a swivel portion, one or more elongate straps, springs or elastic cords, and handles. The swivel portion may allow the elongate straps to rotate without getting tangled. The springs may be placed in series or in parallel with at least part of the elongate straps. Two or more springs, of different lengths, may be placed in parallel to achieve a changing spring constant of the system, depending on displacement of the handle.