Most hardgainer routines focus on training a muscle group once or twice in a seven-day period. For many hardgainers, however, this still constitutes overtraining. Intensity cycling is a popular training system that other people use with good results. Unfortunately, it never works
The 'easy' portion of the cycle only serves to decrease strength, which we then find difficult to regain. Going all out on every set is the only method we've ever found successful. The trouble is, all-out effort, even for a few sets, can quickly result in overtraining. We have to push very hard on a limited number of sets and then not work out again until we have completely recovered.
We currently train once a week, and since I divide my sessions into upper- and lower-body workouts, that means I train each bodypart once every two weeks. I don't mean to imply that everyone should train this way, but I do want to stress that everyone should determine his or her own training requirements instead of simply following some formula.
You can determine what works best for you through minimal experimentation and record keeping. If you cannot equal or exceed the poundages and repetitions from your previous workout, you haven't fully recovered. Muscular growth is a compensatory response to an imposed demand. It's a waste of time to train one moment before complete recovery has taken place. It has to be either a positive adaptation has taken place, or it hasn't. Empirical evidence indicates that one hard set of a basic movement for a major muscle group will give you the best results.
An upper-body workout might look like this: bench press, military press, dumbbell row and barbell curl. I personally prefer very low reps. They provide better overload while minimizing the strain on my joints. In fact, it doesn't matter whether you prefer very slow reps, high reps or low reps; machines or free weights the essential concepts of training remain the same. You have to stimulate growth and allow complete recovery before you train again. Learning this lesson will save you years of wasted effort.