Why do women and girls think they can gain a lot of muscle mass in just a week or two?

Lack of education. You can blame infomercials, dodgy 'fitness experts' and famous figures.

Infomercials have taught us that it is possible to build muscle and lose weight at the same time. Although the two aren't completely mutually exclusive, we switch between being anabolic and catabolic over the course of the day, they have completely overblown the concept making it seem like you can develop serious mass while losing fat >.>

Our dodgy fitness trainers have taught us that 'muscle tone' is something you can build. I can't get my head around this. People think you can actually 'build' tone or 'build' bulk, they think that building bulk just makes you bigger and building tone defines your muscle. This is one the stupidest things I've heard lol, I'm sure you'd agree. I've explained so many times on this forum that your muscle tone is just how the appearance of the muscle alters as your body fat changes and you can only make your muscles bigger or smaller, but people still don't get it.

Evil dictators, such as Oprah (apparently she's actually getting better now she has a dietician lol), have taught us that a balanced diet is insignificant. Don't worry about all those essential nutrients your body needs to function and keep your organ tissue healthy, metabolism, pff, what's that? Everyone knows only eating things deemed 'healthy' will keep your body in top condition! Lets just eat apples and drink tea all day and watch the fat melt away! Stay away from evil things such as carbs and fat because everyone knows they just go straight to your hips, those doctors that claim your body uses them for beneficial purposes have no idea!

(sorry got a bit carried away with sarcasm)

But you can see, a combination of these things (and I'm sure there's many other factors) makes women think they can have these terrible eating habits and it's healthy, they're getting heavier because they must be 'replacing' the fat they lost with muscle mass from their 'toning exercises'.

>.<

The world needs more education lol. I'm certainly not an expert, I live with 2 girls who are med students and in return for the training I give them I learn the technical side of how everything works (today I learnt I can mix my glutamine with acidic things because that amino acid chain can be reformed but not broken down like creatine can heh). But every post we answer here someone learns something new.

We're doing good things here, Seagull. XD

I've never heard that one before and I can't imagine why they'd want to gain a lot of muscle mass, do they want to look like Lenda Murray? Boys and men have seem to thinj this way. A friend of mine at the gym was complaining about how he shouldn't have to lift such small weights becuase its embarrasing, I told him that everyone has to start somewhere, people go to the gym to get strong not because they are strong already.

Ignorance, ha.

We tell ourselves what we want to hear.