Back in the 1970's, Arthur Jones popularized the so-called high-intensity training (HIT, not to be confused with HIIT – high intensity interval training) approach to building muscle. HIT is based on the premise that only a single set of an exercise is necessary to stimulate growth, provided you train to the point of momentary concentric muscular failure.
According to HIT dogma, performing additional sets beyond this first set is superfluous and perhaps even counterproductive to muscle development. Other prominent industry leaders such as Mike Mentzer and Ellington Darden subsequently followed Jones's lead and embraced the HIT philosophy, resulting in a surge in its popularity. To this day, HIT continues to enjoy an ardent following.
Now before I get accused of being anti-HIT, I'll readily admit that it's a viable training strategy. There's no denying that it can help build appreciable muscle. And if you're time-pressed, it can provide an efficient and effective workout.
That said, if your goal is to maximize muscle development, HIT simply doesn't do the trick. You need a higher training volume. Substantially higher than just one set per exercise.
Multi-Set Protocols Are Superior
The prevailing body of research consistently shows that multiple set protocols are superior to single set protocols for increasing strength and size. Meta-analyses published in The Journal of Strength and Conditioning Research show that multiple set training results in 46% greater increases in strength and 40% greater increases in muscle growth when compared to single-set protocols.
Whether the hypertrophic superiority of multiple sets is due to greater total muscle tension, muscle damage, metabolic stress, or some combination of these factors isn't clear. What is clear is that multiple sets are a must if you want to maximize your muscular potential.
Problem is, even if you employ multiple sets it's very possible you're still not training with sufficient volume. The optimal number of sets needed to elicit superior growth will vary from person to person and depend on a host of individual factors such as genetics, recuperative ability, training experience, and nutritional status.
But individual response is only part of the equation. The size of a given muscle also has relevance. Larger muscle groups such as the back and thighs need a higher volume than the smaller muscles of the arms and calves, which get significant ancillary work during multi-joint exercises.
Splits vs. Full-Body Programs
Another important consideration here is the structure of your program. All things being equal, training with a split routine allows for a greater daily training volume per muscle group versus a total body routine.
And if you follow a training split, the composition of your split will influence training daily volume (a 3-day split allows for a greater volume per muscle group compared with a 2-day split). Accordingly, training volume is best determined on a weekly basis as opposed to a single session.
Whatever your target weekly volume, optimal results are achieved by taking a periodized approach where the number of sets are strategically manipulated over the course of a training cycle. Understand that repeatedly training with high volumes will inevitably lead to overtraining.
In fact, evidence shows that volume has an even greater correlation with overtraining than intensity. Only by embracing periodization can you reap the benefits of a high training volume while avoiding the dreaded overtrained state.
Let's say you've determined that your maximum weekly volume should entail performing 18-20 sets per muscle group. Focus on a three-month mesocycle where you target 8-10 sets a week the first month, 14-16 sets the second month, and then culminate with an overreaching cycle in the final month where you perform 18-20 sets per week.
Follow this with a brief period of unloading or active recovery to facilitate restoration and rejuvenation. Given that it generally takes one to two weeks for the full effects of supercompensation to manifest after completion of an overreaching cycle, you should realize optimal muscular gains sometime during the restorative period.