As long as you can either lift more weights, use less rest to get ready for another round, or lift more repetitions than you did last time you're making progress. Muscle soreness can be a side effect for particularily rough workouts when you're adjusting all three parameters at once, but it's not the way to tell if you're making progress.
Start a written training log. Write down what you do, and next time you lift do one more rep on each lift until you hit 12 - then add one more pound and see how many you can do. Just strive to do better than last time, it's the only measurement that matter.
Personally, I work each large muscle group once a week - the level of stress I put on the musculature means it takes from 4-7 days for it to recover.
There are competing theories for how you should work out, though any that are contrary to my opinion is just plain wrong :-P
Seriously though. When I was 16 and just starting with strength training I could do a full-body workout three times a week. fast forward half a year, and I was lifting heavy enough that I had to split the workout into upper/lower and work each half of the body twice a week.
Nowadays, that pace would plain kill me - I don't have the testosterone of a 16-year old boy anymore.
Anyway, that little digression aside, it depends a bit on how long you've been working out, but in general training through deep muscular soreness isn't a good idea. That is, if you've completed warmup and your msucles are still sore, you shouldn't work out, because your body hasn't finished recovering yet.
Some of the bodyweight strength/conditioning routines he demonstrates are very fine strenght workouts as well up to a certain level. That's why he adds in resistance bands, because after a certain point you have to do an ungodly amount of repetitions to get any maximal strength benefit, though you'll develop endurance strength to scary levels.
Have you tried doing Billy's workouts with resistance bands added? If not, give it a shot - should work to put some muscle on you for a while.
'Course, Billy developed his physique lifting heavy weights, but you can make some headway in that direction with the bands - resistance is resistance no matter where you find it, and to develop muscle you just need to work at overcoming resistance.
It's easier to control and adjust weights than bands, and you get a more even level of reistance through the range of motion using weights. Which is most useful to you depends entirely on what your goal is - sometimes the uneven resistance in a band is exactly what you want to use. Punching gets real fun using bands, for example :)
When it comes to post-workout nutrition.. well, I do use a whey protein shake these days just after a workout. Mostly from laziness though - getting some post-workout protein is neccessary, and a shake is easier to make than a proper meal is. And whey protein gets absorbed very fast by your body, so it's a useful component of exercise nutrition when you lift heavy weights.
Except for that post-workout drink though, I stick to eating real food. The idea is to lose weight, and by eating actual food as opposed to drinking shakes you keep your body burning calories to digest your meal :)
I haven't read all the other responses, but according to my trainer, yes, you should be a LITTLE sore the next day. If you're not clenching your teeth and groaning by the end of the last rep of the set, you could work harder.
You should push your self a little more each workout, whether it be with a few extra pounds, or more reps, less rest, etc. . . I personally like to push the fatigued muscles until I couldn't do another rep. Rest 30 secs, and repeat for 1-2 more sets! The last 3 of each set should be the hardest; if you find yourself doing more than 15 reps per set, increase your weights!
Working hard puts me in a state of happy soreness the next day, the kind that you get over in a day or so. If you're sore for more than a few days, you've pushed yourself WAY too hard... In that case, lighten up! Do less!
I will only do weights again when my muscles feel good again, pushing through the soreness doesn't help much to repair the ripped muscle that's trying to re-heal stronger! You'll only be delaying the recovery!
Muscle soreness is a frequent side effect of making gains, yes. But it's not a neccesary component.
There are many times I "feel the burn" but there are more when I don't feel it until I go to do something else the next day - like reach up high in the cupboard for something and feel the muscle in the shoulder or upper chest that I worked the day before say "ouch"
Today my legs were feeling the workout from the cardio class on Tuesday -- I did do squats Monday but it wasn't until today that my legs felt it - so it could have been a combo of the 2 workouts.
Also you don't want to be in pain -- that means injury -- but "feeling" the muscle the day after may or may not happen.
Oh, hi there, Melkor from 5 years ago. Yeah, I still agree with the "no pain - no pain" and "resistance is resistance", but did you notice how switching from body builder to power lifter actually worked pretty damn well from a body building perspective too? Turn out there's an upper stimulus threshold for muscle growth as well as a lower stimulus threshold and you just don't need to completely annihilate any given set of muscles to see improvements. With training closer to that upper bound of maximal stimulus instead of maximal annihilation you could train more frequently without beating yourself down each time, so while you're not 16 or even 35 anymore, you're doing pretty damn good if I say so myself.
So after I finish my set of squats and my legs feel wobbly and I can barely walk I'm doing it wrong!?!?
Why didn't you tell me this earlier!
(I'm being facetious, of course)
u wot m8