Putting on muscle while staying lean
This is extremely difficult.
If you observe how professional bodybuilders cycle their workouts through the year, they CYLCE their workouts and their nutrient/drug intake.
After the majority of the major competitions are over, they go into a RECOVERY phase where they may take some time off training and relax.
They then generally work back into building up the intensity of their workouts through a BULKING UP phase, during whick they put on maybe 50 pounds of MUSCLE AND FAT. This is a GROWTH PHASE.
When competition season nears, they will enter into a CUTTING UP phase, during which they will increase the use of fat burners, diuretics, etc, and will lose maybe 30-40 pounds of the weight they put on.
So, for example, the TYPICAL situation for a bodybuilder might go like this:
1 - competitive season, bodybuilder competes at 240 lbs at 3% body fat
2 - relaxation/light phase, bodybuilder puts on a bit of fat, but gives nervous system and endocrine system a rest
3- Anabolic/bulking phase, bodybuilder focuses on lifting heavy, eating as much as possible, anabolic drug use, ends up at 300 lbs
4- cutting phase. Reduce the weights to save the joints, increase rep range, use "shaping" exercises to fine tune muscle appearance. Will lose maybe 40 pounds of FAT AND MUSCLE.
5- Competition phase again, bodybuilder competes at 250 pounds
Competitors do it year after year. If you look at a bodybuilder off season, they are MUCH larger than when in season, but will look puffy and out of shape. But they are a great deal stronger in the off season.
Drastically cutting fat in a short period of time is catabolic to both fat and muscle. Loss of strenth is inevitable, expected and accepted. The goal is to lose more fat than muscle, and to end up with more muscle than you carried during competition the year before.
If you follow the careers of Dorian Yates and Ronnie Coleman (the last two MR. OLYMPIAS over the past decade), you will notice that they come in a few pounds heavier every year, and are MUCH larger and stronger, yet less AESTHETIC off season.
I'm NOT SAYING that putting on size while staying lean can't be done, just that you WON'T BE ABLE TO GROW AS QUICKLY as when trying to focus exclusively on size.
Similarly, you WON'T BE ABLE TO CUT FAT AS QUICKLY if you are also trying to build size.
Anabolic hormones (Size building and fat storing) and catabolic (Tissue and fat breakdown/loss) hormones, and the mechanisms that regulate their release, are in constant opposition in the body. Optimizing one will INEVITABLY COUNTERACT the activity of the other.
That said, there is a large range of options in terms of how quickly you want to do one or the other. It IS NOT BLACK AND WHITE, but THERE ARE COMPROMISES REGARDLESS.