筋肉
きんにく · kinniku · JLPT N3 · noun
muscle
💪🍖 筋肉 = sinew (筋 kin) + flesh (肉 niku): the tendons plus the meat on them
筋 (kin) means sinew, tendon or fibre; it has 竹 bamboo on top, because bamboo is stringy and fibrous. 肉 (niku) is meat or flesh, the same niku as in yakiniku. Put the fibres and the meat together and you get muscle.
筋 — bamboo 竹 + flesh 月(肉) + strength 力
A semantic compound: 月 (flesh) shows it relates to the body, 力 (strength) hints at muscular force, and 竹 (bamboo) suggests fibers like bamboo strands. Together they depict the sinews or tendons that give the body its strength.
肉 — pictograph of a slab of meat with ribs/striations
肉 is a pictograph originally depicting a piece of butchered meat, showing the outer cut and the striations of muscle or ribs inside. The character has meant 'flesh' or 'meat' since oracle bone times. As a radical it is usually written 月 on the left or bottom of characters relating to the body (e.g. 肝, 胃).