Let's start with the most basic idea behind all of fitness - adaptation.
Whenever we impose any kind of stress on our bodies -- whether that be via weight training, steady state cardio, HIIT, plyometric training, or any of the many other modalities -- we are hoping for our bodies to ADAPT to that specific stress. We want our bodies to burn fat, to build muscle, to enhance neuromuscular control and performance. We want adaptation.
There are four main categories of adaptation we can strive for when it comes to weight training, and those categories are muscular endurance, hypertrophy, maximal strength, and speed/power. There are designated set and rep schemes that have been proven to be most effective for achieving adaptations specific to each of those four categories. Before delving into what those set and rep schemes are, let's first discuss what each category of adaptation is…
MUSCULAR ENDURANCE by definition is "a muscle's ability to contract for an extended period." (pg 9) But what does that mean practically? Essentially it is an adaptation that allows for prolonged muscle contraction; longer term strength.
HYPERTROPHY is simply the increase in the size of muscle fibers. This goal is more often than not desired for aesthetic reasons; think bodybuilder. Hypertrophy = bigger muscles.
MAXIMAL STRENGTH is the muscle's ability to produce maximal force in a minimal amount of time. This is different from muscular endurance in that you are only producing force for a short, versus a prolonged, amount of time. Here is a functional comparison; imagine deadlifting 100 pounds for 20 reps vs deadlifting 350 pounds for one rep. The 100 pound/20 rep deadlift is more akin to muscular endurance while the 350 pound/single rep deadlift falls in line with maximal strength. For this adaptation think powerlifter.
SPEED/POWER is a broad category that refers mostly to sports performance. These kind of workouts consist of a lot of jumping, throwing, and very quick repetitions. The adaptations that occur are more neuromuscular meaning that they are concerned with the linking and efficiency of the nervous and muscular system together.
Now that we've got that covered, what is the best way to train for each adaptation?
MUSCULAR ENDURANCE is best achieved by a low amount of sets and high reps at a lower intensity with short rests in between.
Sets: 1 - 3
Reps: 12 - 20
Intensity: 50 - 70% (of one rep maximum [1RM])
Rests: 0 - 90 seconds
HYPERTROPHY is best achieved with a moderate amount of sets and moderate reps at a decently high intensity with very short rests. In other words, you want to have a lot of volume in hypertrophy workouts using weights that still challenge you. Don't go too light!
Sets: 3 - 5
Reps: 6 - 12
Intensity: 75 - 85% (of 1RM)
Rests: 0 - 60 seconds
MAXIMAL STRENGTH is best achieved with a high amount of sets, low amount of reps, very high intensity, and long rest periods. You want to be using very heavy weights and giving your body ample time to recover between sets. And, since you're doing a low amount of reps in each set you will be doing more total sets.
Sets: 4 - 6
Reps: 1 - 5
Intensity: 85 - 100% (of 1RM)
Rests: 3 - 5 minutes
SPEED/POWER is best achieved with fast/explosive movements using light weights. You will want to do a moderate to high amount of sets for a low to moderate amount of reps. Rests for speed/power adaptations will be very similar to maximal strength.
Sets: 3 - 6
Reps: 1 - 10
Intensity: 40 - 35% (of 1RM) or about 10% of your body weight
Rests: 3 - 5 minutes
(All set/rep/intensity/rest information came from Chapter 14, page 360, table 14.1.)
NOW… with all this being said, it is also important to note that in order to make progress in any one category you do NOT need to stick 100% to the set/rep schemes outline above. It is quite okay to mix and mingle the different training styles. However, the set/rep schemes above are going to be the most efficient way to achieve whatever adaption you're looking for.
Lastly, for anyone who is not familiar with the term "1 rep max," it is the maximum amount of weight you can lift for one single rep. If you do not know this number from practice there are many calculators available online. Just try Googling "1 rep max calculator."
NASM Essentials of Personal Fitness Training. Fourth Edition. Michael A. Clark, Brian G. Sutton, Scott C. Lucett. 2014.