It is said that this another name derives from the fact that, when he was born, the muscle of his arm was bulging like a Tomo (a tool to be wound around the left arm when shooting an arrow).
この別名は天皇が生まれた時、その腕の肉が鞆（とも。弓を射る時に左腕に巻きつける道具）のように盛り上がっていた事に由来するという。