It turns out, despite his feeble looks, that Nikolai is a Master of Sports in sambo. note "Samooborona bez oruzhiya", literally "self-defense without weapons" - a form of martial arts invented in the USSR.
Zig Zagged: Nikolai is only able to temporarily turn into a muscle-bound war machine, and he cannot control the mechanism that enables this transformation, so he randomly shifts from feeble Russian scientist to super-strong meat head.
Enforced: The good old USSR is putting out this film, and they would like to portray their soldiers as impressively as possible
Lampshaded: "The new guy reminds me of bears... he has to be Russian".
Invoked: As a kid, Nikolai is impressed by the achievements of the Soviet athletes and decides to start training himself.
Exploited: Whenever the heroes are on the adventure, Nikolai always takes point, because he's the strongest guy in the party.
Defied: Nikolai was never predisposed to physical strength, so he chose to go with the flow and pursue a scientific career instead.
Discussed: "Okay, there is no way every man in Russia can bench press 400 pounds..".
Conversed: "Why are Russian people always portrayed on TV as huge and brutish?" "From exagerrating the facts and to Red Scare, there are a lot of reasons".
Deconstructed: Because of his outrageous size, Nikolai beings to develop several health issues, including high blood pressure and heart palpitations. Before too long, he cannot even stand on his own and is completely bed-ridden.
Reconstructed: Nikolai undergoes special treatment to prepare his body for being so large and muscular, which is able to prevent all of the adverse size-effects.