One of the more popular muscle mass building programs that is being used right now is the 5x5 program. Essentially this workout is designed to hit your muscles hard three times per week and then allow enough time to promote growth and recovery. It was designed for strength athletes because one of the most common effects seen by it is an increase in strength.
Along with the strength however you will most often see an increase in muscle mass as well, provided you are eating enough calories to support this muscle growth.
It should be noted too that you should have a good deal of base training behind you before starting a program like this. The intensity and volume are higher so if your body is not used to dealing with higher loads it is going to wind up having a hard time recovering and you could risk overtraining.
What the 5x5 program specializes in is periodization, which is changing the program as you progress through it to constantly change the stimulus, promote increases in strength by further challenging your muscles each week and then also having enough recovery time built in with an easier week so as to not become overtrained.
You are basically going to complete the 5x5 program for a total of 7-9 weeks, which includes 4-6 weeks of prep work and then a 3-week peak phase. After you have completed the full cycle it is a good idea to do a deloading week where you workout with less intensity or if you prefer just take a week for complete rest.
Prep Work
During the first week of the training program you should error on the cautious side to make sure your body has a chance to grow accustomed to this type of training. It is likely going to be something you aren't used to so you need to allow for adaptation to take place.
Choosing Your Weight
During this week you will pick a weight that you can do for a total of 5 sets with 5 reps. This weight shouldn't be so easy that you feel you could do a lot more than that but likewise it shouldn't be so hard that you are not able to complete the given protocol.
One of the most essential factors of this program is that you do in fact do 5 sets of 5 reps. It is a key factor in the success of the program and must be followed.
Before starting the first week it would be a good idea to set a 5 rep max for each of the exercises (as described later) so that you know what weight it is you are specifically trying to beat. During the first week you want to use a lesser weight since obviously you do have 5 sets to complete rather than just the one you used for your rep max test.
Bumping It Up
If after the first week you have managed to successfully complete all your sets at a specified weight then bump it up 5-10 pounds for the following week. Again here, if you bump it up and are not able to successfully complete all the reps with proper form then this is too high of an increase and you need to be more moderate.
If you have really been struggling to lift the amount of weight you were using however then you will want to keep it the same for one more week and then hopefully after that you can raise it higher.
By the time you hit weeks 4-6 you will hopefully be setting new rep maxes and will be seeing a significant increase in strength, provided you are in a caloric surplus. You can sometimes still see strength increases even if you are in a deficit however it is much more unlikely, especially among advanced individuals.
Peaking Phase
After you have finished with this prep phase (ending after week 4-6) it is then time to move onto the peaking phase. What you will do for the first two weeks is drop your sets and reps down to more of a 3x3 set-up. This will allow you to push each set even harder and therefore hopefully lift more weight, thus upping your max.
You may also want to only perform the squats twice per week rather than three times to allow for extra recovery since the large leg muscles take longer; especially while lifting with such intensity.
During these few weeks the most important thing you must focus on, even moreso than getting in the reps, is the weight increases. This is your peaking phase after all so you want to be pushing yourself to new levels.
Finally for the last week of the cycle you can take it down to one set of three for 2-to-3 workouts and maybe even try for single reps maxes at the end. It should be noted though that not everyone will choose to do the single rep maxes, one set of three or even the 2-3 weeks of 3x3 set-up.
If you choose to end the cycle after the initial 4-6 weeks of 5x5 that is alright too and in some cases, such as for those who are training for sports, the intensity levels during the peak phases are just too much for them to handle along with their other physical pursuits.
Moving on to the exercises now, here is what the set-up will look like.
As with any program you need to ensure you have proper pre and post workout nutrition while doing this. The workouts are going to take a lot out of your body so providing them with the nutrients to fuel the activity as well as recovery from it is essential if you hope to make progress.
Conclusion
So if you are looking for a new workout to try and already have a few years of training behind you, give this a chance. If done correctly it is hard not to see good results from it and you will likely be more than happy to go on it again for a second and third cycle in the future.