The M.U.S.C.L.E. figures were based on the Japanese toyline called kinkeshi. Kinkeshi were based on a manga and anime called Kinnikuman, and some figures were based on anime-only characters. The main hero was Kinnikuman, who, in the US, was renamed Muscle Man and was the leader of the Thug Busters. He was described as the greatest wrestling champion. The only other named figure in the US line was Buffaloman, who was renamed Terri-Bull, and said to be the leader of the Cosmic Crunchers. Some of the figures were sculpted to resemble popular wrestlers who had competed in Japan such as Terry Funk, Dusty Rhodes, Abdullah The Butcher, and Jushin "Thunder" Liger.
The first shipment of figures were all a 'bubble-gum pink' color the collecting community calls 'flesh.' The second shipment was a half-and-half mixture of flesh and either dark blue, red, or purple figures. The third shipment contained no flesh figures, only dark blue, red, purple, magenta, salmon, lime green, neon orange, and light blue. Five figures came with the boardgame in an exclusive grape or light purple color.
In addition to packs containing only figures, there was a mail-away poster, a Battlin' Belt display case, and two games released that made use of the M.U.S.C.L.E. figures.
The Hard Knockin' Rockin' Ring game was a plastic wrestling ring with two small clamps for figures and that played much like Rock'em Sock'em Robots. The M.U.S.C.L.E. board game was a unique battle-royal style game where teams of five figures of two different colors fought.
The Hard Knockin' Rockin' Ring came with two exclusive flesh figures not released in the regular line of toys, a slightly smaller version of #141 (Muscleman) and a Terri-Bull. The Board Game also included the same sculpt of Terri-Bull in lime green.