The popularisation of “Man-Amplifiers” was largely due to the movie “Aliens” directed by James Cameron and released in 1986. Earlier scenes introduce it as it is, a power loader for heavy materials. Ripley later uses it as an equaliser for a “mano e mano” with the queen alien.
Earlier concept by Syd Mead.
Later designs by James “Jim” Cameron himself.
See the earlier 1967 “The Ambushers” movie with its Power Loader here.