A look at the early James Bond reveals that Bond wasn't a big musclebound guy; in fact he has been described as being quite the opposite. In Ian Fleming’s novels, particularly in “From Russia With Love”, Bond is described as a slimly build 6-foot tall man weighing about 168 Pounds. Given that the character has been described as a heavy smoker, one can quickly assume that Bond wasn’t the gym type of agent.
But, counter-intuitively, that's all good! Just look at the real life Navy Seals and you'll find that, although they probably don't smoke, most are more sinewy than muscled, and of very average height.
In the early Bond movies starring Sean Connery, Roger Moore, Timothy Dalton and George Lazenby you can tell that, physically, the creator of James Bond wasn’t concerned too much with shoulder span, torso and arms size or whether he had a six pack to display on the beach. Same goes for chest hair, if somebody cares about this stuff. The rebooted Pierce Brosnan version of Bond was a bit fitter than most of the other incarnations, but even then you wouldn’t find him to be muscular in the way that Craig is. In Iraq and Afghanistan, as we just saw, those muscles would have just gotten him killed.
The manly man of the original Bond wasn’t about muscles. Bond was created to be a charismatic, extremely worldly Import-Export executive, yet a cunning character that could talk himself out of a dangerous situation and fight only when it was the only option left. What good is a secret agent that draws attention because he/she picks fights?
When James bond was created he was ready for the Jet Age, when you could believably transport the action from one country to another with just a second unit camera shot of a jet plane taking off, immediately followed by another of the same plane landing.
With the advent of Marvel’s heroes dominating the big screen and changing the notion of what the hero must look like, the Bond franchise producers had to make changes to reinvent a Bond that was fit, muscular and ripped to be accepted as a hero against those Hulk, Thor, et al, blurring the line between hero and superhero.
Blending in and the real life spies of today.
From a cinematic point of view Bond had to be beefed up, more muscular and less hairy in order to fit among the heroes of today dominated by the Marvel universe. However, if you are to take a real life perspective on the super spy, you would be best to be matching the average size and build you are trying to blend in with.
A colonel I worked with in Bosnia mentioned a bunch of black ops that were trying to infiltrate the Serbs lines pretending to be Doctors Without Borders. "The Serbs were not idiots,” he said “they knew these guys were not who they pretended to be. They all looked like they had been heavily trained. It was not your usual subscription-to-the-gym kind of fitness that you would expect from Doctors Without Borders."
Bond’s life span through multiple eras each of which Bond had to adapt to fit in with his contemporaries. Many actors over the years brought to the screen the spirit of the current generation as they incarnated Bond, each time slightly adapted from the original, with Craig's Bond the most visible departure. Paradoxically, Craig's Bond is much more manly, yet less macho in his attitude towards women than his predecessor.
Most likely, this is why Bond is still considered a reference today.