The first duel is story related, you can loose but you can retry as many time you want.
To win you must wait the signal and then push
fast as you can. Sometimes you must also press
Win five time to unlock the achievement. This is cumulative.
Against your first opponent, winning three matches is easy, the 4th is hard and the 5th is impossible. There is an other place to do this after the cutscene with Joy (woman on bike) one min later in the corner opposite of where she came.
Just next to the second location, you can see stairs going up on a rooftops. There are two or three more guys to challenge there !
Evandalist said :
There are 6 separate arm wrestling opponents in Aberdeen, with an additional 6 to take on on Kowloon, for a total of 12 opponents across the game. Each opponent has its own difficult level as well. Furthermore, the higher your money bet the harder the difficulty. One of them (Dory Gordie) is actually impossible to beat on the $100 bet, even with use of a turbo controller and knowing all the QTE prompts beforehand.
Moving crates at work consistently helps build Ryo's arm strength and makes arm-wrestling matches somewhat easier. It's a very slight and subtle change in strength, but it gives you slightly larger windows of opportunity to correctly input the QTE sequences. Unfortunately, it won't help with mashing on those high money matches against the game's tougher opponents.