Many people believe that the key to more muscle growth is to train infrequently. Well, they're wrong. Usually.
The logic behind infrequent training (three or fewer sessions per week) is that muscle grows while you're resting. Proponents of infrequent training claim that only drug users can train often and recover. They say a natural lifter needs a lot of rest days to grow from his efforts.
Here's Why That's Wrong
First, physical activity and more training can actually speed up the recovery process by releasing cytokines. Training more frequently, as long as intensity and volume are properly adjusted, will likely make it easier to recover from training.
Second, the more frequently you ask your body to perform and recover from physical work, the better it becomes at recovering from such sessions. The body is built for adaptation, which means that the more often you perform a certain type of effort the easier it'll be for your body to handle it. So by training infrequently you're actually preventing your body from being able to recover efficiently to training.
Frequency of training means how many times you're training a week. So by infrequent, I don't mean training each muscle infrequently (once a week). You could train every day and hit each muscle group only once per week. This would be a high frequency of training.
Training has a systemic effect on the nervous, hormonal, and immune system. Not to mention that there's some overlap when training. For example, the lats are supporting muscles involved in the bench press, deadlift, and squat. Even when you're not training back they might still be involved. So it's important to sort this out.
But what if It DOES lead to better recovery?
Let's pretend that including a lot of rest days in your week actually did help you recover. The benefit of infrequent training would be to allow you to perform more physical work on the days you train. For that reason, infrequent but high volume training might actually work quite well for some people. Trash yourself every workout, but give yourself ample recovery time.
A low volume of work performed infrequently won't challenge your body's recovery capacities, so positive adaptations (muscle growth, strength gains) will be low or nonexistent. It also wouldn't require 4-5 recovery days per week. Even the bottom of the genetic food chain can recover quite fast from a low volume of work.
If you're someone who doesn't tolerate volume well, yes, use a lower daily training volume. But the overall training frequency per week will need to be higher for maximum results, and so that your body becomes better at recovering from physical stimulation.
Infrequent and low-volume training would only be the best solution for those who are working a physical job. The demand of their job makes it so that they won't have as much energy to spend on training. But also the physical aspect of their work will initiate the cytokine response that helps with muscle recovery, and since they're working physically every day, they'll get the benefits of frequent training on the capacity to recover from physical work.
Ironically enough, the population that would get good gains from low frequency/low volume training are those genetically gifted to build muscle, because they don't need much stimulation to grow.