Keshigomu figurines are small, inexpensive rubber figures made of a solid mold and cast in bright colors or flesh tone. Somewhat stretchy, they are used as both erasers or collectibles. The designs range from wrestlers to robots, aliens to monsters, and every anime in-between.

In 1984 Select released a series of Keshigomu figures from Japan, a full two years before Mattel brought their M.U.S.C.L.E. toy line to market. The first wave was called “Muscle Men,” before quickly being rebranded to “Musclemania.” The line consisted on 12 figures in six colors. In 1986, 12 more figures were released, this time with an additional seventh color. 

More information can be found at the fansite University of MUSCLE.