The more serious heavy compound exercises, like squats or DL's will certainly boost the metabolism greatly, which in return releases growth chemicals/hormones into the blood stream; hence the muscle cells themselves become larger, with strength also increasing.. The squat & DL are whole body movements, from the feet to the neck.
Some have used only the squat or DL as a one exercise workout (no other exercises in that workout) and found muscular gains in the chest, back and even arms. Stimulating natural HGH are a factor here. Squats or DL require a lot of expended energy if done with serious intent. Reason why they should be done as a first exercise in any full body, short workout plan, to take full advantage of their benefits. Having them at the end of a full body workout is self defeating, because full justice can not be done to these exercises.
Might be a surprise to some, but even higher reps with the squats and DL's can produce wonderful results. Some of my best gains were with heavy 20 rep breathing squats. Also used this method with DL's, Hack BB squats. The ultimate (my veiw only) is the squat clean and jerk-press, from 12 to 20 reps. Think your in cardio shape, than give this one exercise a serious try. Might be surprises.
Good Luck.