The Bullworker is an isometric exercise device used for strength training originally marketed and sold in the early 1960s. Designed and patented by German inventor Gert F. Kölbel, it continues to sell in Europe, Asia and the United States. Over 9 million units have been sold worldwide.
The original Bullworker consists of two sleeved, spring-loaded, telescopic cylinders in the center, with two hand grips affixed at the outermost ends. Two opposing cables are attached to the hand grips at each end of the device. The apparatus weighs about four pounds. Exercises are performed by pushing inwards on the contractible cylinders or by pulling the cables outwards, away from the cylinders. The resultant compression of the internal spring creates the desired resistance; the Bullworker returns to its original position when pressure is released. A range of up to 150 pounds or more of resistance is possible.
Although a number of improvements have been made to the Bullworker since its introduction, the unit remain basically the same. It is marketed worldwide, with trademarks and distribution owned by Hughes Marketing, LLC. As of 2013 there were two models, the Classic and Steel-Bow. The Classic is a "barbell" size with greater resistance, approaching 150 lbs, and the Steel-Bow is a "dumbbell" size with interchangeable springs for changing resistance levels, ranging from 0-100 lbs of resistance.
The original suggested 26 individual exercises. While isometrics was the emphasis, the instructions included isotonic, cardio, resiliency and endurance routines. The emphasis on these additional functions greatly expanded the number of exercises available. An additional fitness routine of Iso-Motion has since been added. Bullworkers are durable; many early units remain in use.