Originally Posted by SystemicAnomaly
Altho' you don't see it in his arms, he does show some evidence of muscle tone in his shoulders, torso/core (chest and abs) and legs. His body fat % is considerably lower than Serena's. Serena's overall size of a combination of muscle size and a higher fat content (her ample mams are clear evidence of that body fat content).
Roger undoubtedly has a fairly high % of fast-twitch muscles fibers (both type IIa and type IIx). These type II fibers produce power (speed strength). They do not necessarily need to be huge to produce power. Bodybuilders will often have large muscles and can lift/press large amount of weight but will not necessarily be able to produce a lot of power. For instance they might not be able to throw a ball very hard/fast or sprint very fast either. Powerlifters or Olympic weightlifters, OTOH, have developed both power and size (but not always definition).
I may have it wrong but I thinks that type IIa fibers can be developed to increase muscle size significantly. OTOH, type IIx fibers (and the slow-twitch, type I fibers) do not increase much in size. I'm certain that this is true for type I fibers, but not absolutely sure if I've got it right for both type II fiber types.
Serena probably has a decent amount of fast-twitch fibers but her muscle fiber profile is probably not the same as Roger's. Even if she could bench press more than Roger, it seems unlikely that she can produce quite as much leg power, core power or shoulder power as Roger.
How much does she claim she can bench? Just remember that big muscles doesn't mean extra strength. When she actually is standing next to the likes of Federer and Nadal, you can see she's not looking imposing at all. She's small compared to them. And these guys don't exactly live in the weight room.