What Really Works?
As many intelligent gym enthusiasts will tell you, and as I will further attest, lifting progressively heavier and heavier weights over the course of weeks, months, and years works for building muscle. Of course, while progressive overload is by far the means for growing muscle, if you've perused the internet, for any amount of time, looking for the latest and greatest workout program that will allow you to look like your favorite superhero, action hero, or athlete, you no doubt have discovered the uniform lack of uniformity among the various muscle-building methodologies in existence. One person advises "blitzing" every muscle group once per week with a barrage of exercises, using high volume and high intensity. Another advocates using an upper/lower body split using moderate weights, with moderate intensity, hitting each muscle group two times per week. Still another says you should only do full body splits, hitting your whole body two to three times per week with a lower amount of volume and high intensity. I could wax on and on here, but I've made my point: there are a lot of ways to get bigger, but, what all effective methods have in common is their reliance upon progressive overload.
Sweating the Details
Regardless of methods, one myth (or at least a common misconception) that echoes through the halls of gyms everywhere is "You have to lift heavy weights!" Now, I don't want to totally disparage this myth. After all, you can indeed get big by lifting heavy weights (and I mean heavy weights!), but lifting ball-bustingly heavy weights is not the only way to build muscle (and for some perhaps not the best way).
Most people worth listening to in the fitness business are in pretty universal agreement that lifting weights in the 6-12 rep range using 70-80% of your 1 rep max, hitting a muscle group 1-2x per week, is ideal for growing muscle. Of course, there are a few others who espouse lifting weights in the 4-6 rep range using up to 85% of your 1 rep max, and there are those who say you should use weight in the 15(+) rep range using less than 70% of your 1 rep max. Nevertheless, most people "in the know" will tell you that your best bet is to stick to weights in the 70-80% intensity range (give or take).
Now, most studies done on muscle building back up this consensus, but consequently, most studies only conduct their tests in the 70-80% intensity range (hence, the reason most studies uphold this generally accepted recommendation). However, not all studies are so narrowly constrained. If you look around for bit, you'll find some very interesting studies that demonstrate the effectiveness of using weights as light as 30% of your 1 rep max. Such evidence explains why people can build muscle doing lots of push-ups and other sorts of body-weight-only exercises.
Yet, as you may now protest, while body-weight-only exercises may work initially, in the long-term they only lead to stagnation. True, but this stagnation occurs because your body has adapted to your body weight, not because using higher reps and lighter weights invariably leads to stagnation. You stop building muscle because you fail to use progressive overload. It's that plain and simple.
A Better Way
"Better" is of course relative, but I'll try my best to convince you that using lighter weights to build muscle is in fact better than using heavier weights.
Beyond the fact that using lighter weights works, what is it about using lighter weights that is superior? My answer to this question is simple: joint health!
One of the biggest impediments to building muscle, especially in the long-term, is joint fatigue and joint injuries. Moreover, while muscles typically require 48-72 hours to recover and super-compensate following a workout, if you lift heavy weights, more than just your muscles get damaged; your joints, ligaments, and connective tissue likewise take a beating. What's more, these other damaged components of your musculoskeletal system require much more time to heal (1-2 weeks in some cases). Not only will weakened joints increase the likelihood of injury (which will put a definite kink in your plans for building muscle), weakened joints will also impede your muscle's ability to do the adequate amount work required to make them grow. Whenever a joint is any kind of wonky position, your brain will send signals to the surrounding muscles to tell them to "shut down." This signal will likely be sent before you've been able to optimally damage your muscle fibers and tax your sacroplasmic energy reserves.
Using lighter weights allows you to bypass these issues.
How Light?
You could conceivably go as light as you want, but regardless of the intensity you use, you must go to the point of muscular failure for at least one set of an exercise, and you must use the principle of progressive overload.
What to Do
The methodology I recommend admittedly is not my own. It comes from Jonathan Lawson, who, after doing a good amount of research and anecdotal experimentation, has developed an effective method for building muscle that allows you to use light weights (in some cases ridiculously light weights) to effectively build muscle.
Of his various recommended methods, two in particular have worked well for me: 4XMass and TORQ. These methods are very simple:
For 4XMass, use a weight that's approximately your 15 rep max and do 4 sets of 10 reps. Now, that may seem simple enough, and even easy, but the key to making this method work is the short rest time between sets (only 30-35 seconds). I can assure you that by the time you get to set 4, getting 10 reps will be a struggle! The progression is simple: go to failure on the last (the 4th) set, and if you can get 10 or more reps, increase the weight at your next workout.
For TORQ, do 3 sets, the first for 30 reps, the second for 20 reps, and the third for 15 reps. You'll rest 45 seconds between sets. The goal here is to feel the burn (and if you do it right you'll FEEL IT!). You'll want to use a weight that allows you to just barely get 30 reps for the first set. If you can get 30, 20, and 15 reps successively, add weight at the next workout.
You can use these methods in any number of arrangements, so I have no specific recommendations. But, the following routine is what I'm currently doing, and so far I enjoy it, and I can already tell you that my joints feel amazing since I've started using these methods for building muscle.
Workout A (Upper Body)
Chest & Back
Dips 4 x 10 (or max reps)
Chins 4 x 10 (or max reps)
Dumbbell Incline Bench Press 4 x 10
Dumbbell Chest Supported Row 4 x 10
Dumbbell Incline Bench Chest Fly 3 x 30, 20, 15
Cable Pullover (for Lats) 3 x 30, 20, 15
Shoulders
Standing Dumbbell Press 4 x 10
Dumbbell Upright Row 4 x 10
Seated Arnold Press 3 x 30, 20, 15
Dumbbell Lateral Delt Raise 3 x 30, 20, 15
Arms
Barbell Curl 4 x 10
Close-Grip Bench Press 4 x 10
Zottman Curls 3 x 30, 20, 15
Seated Dumbbell French Press 3 x 30, 20, 15
Workout B (Lower Body)
Legs
Barbell Romanian Deadlift 4 x 10 (I do 1 light warm-up set)
Leg Press 4 x 10
Leg Curl 3 x 30, 20, 15
Leg Extension 3 x 30, 20, 15
Traps
Barbell Shrug 4 x 10
Calves (Do as a circuit)
Wide Stance Calf Press 4 x 10
Medium Stance Calf Press 4 x 10
Narrow Stance Calf Press 4 x 10
Abs (Do as a circuit)
Any Exercise 3 x 30, 20, 15
I workout 3 days per week on Monday, Thursday, and Saturday (provided my schedule permits me), alternating workouts each day. While these workouts seem like they would be long, I'm actually in and out of the gym in just over an hour (primarily because the rest time between sets is so short).
The above program is by no means my recommendation for anyone and everyone. It's simply an example of what I do. Feel free to use what works for you, toss what you dislike, or just make your own workout from scratch. If you're an experienced trainee, I'm sure you don't need me to tell you what to do, but if you're new to training, I highly recommend you find someone (a trainer, a mentor, someone with half a brain) to help you out.
The above program is by no means my recommendation for anyone and everyone. It's simply an example of what I do. Feel free to use what works for you, toss what you dislike, or just make your own workout from scratch. If you're an experienced trainee, I'm sure you don't need me to tell you what to do, but if you're new to training, I highly recommend you find someone (a trainer, a mentor, someone with half a brain) to help you out.
Happy lifting! And may your joints forever thank you!