Building muscle and losing fat

Not sure where you got that information - but I have lost 100lbs in the past year - and built some muscle in the process.....I do two (maybe 3) weight training sessions a week with a PT - and the weights I now lift / move compared to a year ago is very different - and would not be possible without having built some muscle.....

Also with the fat dissapearing I can now actually SEE those muscles!!

I can also see the results in my every day life - my legs are much stronger - I can climb stairs, my knees are much better - as the right muscles now support them - my shoulder strength have increased dramatically - all these things because I have increased the muscle strenght in those areas....

Have I built as much muscle as someone that is not on a calorie defecit - maybe not - but I have definitely built muscle - and all the while losing 2lbs a week!!

It's well known that it is incredibly difficult, and impossible for your average dieter, to put on muscle MASS while eating a calorie deficit. Your muscles cannot create new matter out of thin air. However, working those muscles will cause them to strengthen (just not increase in size) explaining your strength improvements. Also, strength exercises help preserve your muscles as you lose weight, so more of them are left in the end, and they look bigger because less fat covers them.

If you ate at a deficit every single day I doubt you built muscle mass, though.

It is possible to lose fat and build muscle at the same time.

But it's a phenomenon that's generally limited to people who are very overweight and have never lifted weights before, or those who are returning to exercise after a layoff, where muscle memory comes into play.

For example, this study of overweight beginners shows an average 16 pounds of fat lost and 10 pounds of muscle gained during a 14-week period:
http://www.thefactsaboutfitness.com/research/build-muscle-calorie-deficit.htm

So unless you're an overweight beginner, returning to exercise after a layoff, very genetically gifted or using drugs, you're not going to be able to do both at anything approaching the same rate.

In other words, it's far more realistic to lose 10 pounds of fat while gaining a pound or two of muscle. Losing 10 pounds of fat at the same time as replacing it with 10 pounds of muscle is just not a realistic goal for most people, for the reasons I've explained here:
http://www.thefactsaboutfitness.com/research/gain.htm

Mostly, the goal of strength training during weight loss is to prevent muscle loss, not to gain muscle. Of course, preventing yourself from losing 10 pounds of muscle is pretty much the same thing as losing those 10 pounds of muscle, then gaining them back over the next few years, it's just fasted.

It's not completely impossible to gain muscle if you are on a very slight calorie deficit, just very hard. Fat2Fit reported a few weeks ago on a study of elite athletes in weight loss mode while training heavily. One group lost 0.7% of their weight per week and showed a slight muscle gain, while the group that lost 1.4% of their per week maintained their muscle.

http://www.ncbi.nlm.nih.gov/pubmed/21558571

In practice, most of us don't have at least one of the time, skill, or motivation to train like elite athletes, but it's theoretically possible with slow loss and effective, substantial training. (They all followed their normal training schedule PLUS four additional strength workouts per week).

ok, so to be clear if I want to drop inches I weight train, worrying more about building muscle and make sure I eat my exercise calories back. If I want to lose weight I dont weight train as heavily, and eat a deficit?

I'm new to this, but at some point it will all make sense LOL

Always weight train. Always eat your exercise calories (MFP will handle the deficit). Just work out intensely and eat till 0 calories remaining. It couldn't be simpler.

^ do what Taso says. For 2 years I have been lifting and eating at a calorie deficit. The actual lbs have come off slower but the muscles that are already there (probably without building new) are more defined and since the layer of fat is gradually coming off the muscles are more noticable, giving that muscular look you are probably after. I also like the athletic, fit, muscular look which is why I consistently from day one kept strength training in my routine. No "skinny fat" for me! Train hard, eat healthy (and all your calories) and this works!