A large percentage of you are using resistance training and trying to get stronger. You're lifting "X" amount of resistance for "Y" number of repetitions and over "Z" number of sets. Good for you - if this plan is working. 
If it isn’t working, ask yourself these questions about your plan:
  1. Is it based on the underpinning principles of overload-recovery-progression?
  2. Is it an uncomplicated system?
  3. Does it show you progression on a regular basis?
  4. Is it truly creating muscle overload effectively?
Breaking Muscle Shop

Rep Range Is the Essence of Progressive Training

Depending on your answers, it may be time to restructure your plan to something more direct, simple, and based on proven science. You cannot stray too far from the principles of muscle overload, adequate recovery time, and progressive (more demanding) training, so why not use a system that is the essence of it? 
strength, 1 rep max, power, strength training, repetition
If you’re looking for a sound remedy to your out-of-control program, look to the time-proven, but underrated repetition (rep) range as a means of accurate and progressive training.
I'll discuss the beauty of the rep range shortly but first, take a look at two training systems that have flaws. There is the unstructured 3 x 10, 10-8-6, 5 x 5, or whatever sets-x-reps system. There is also the more structured percentage of a one-repetition-max (1RM) system implemented with specific loads but with arbitrarily assigned reps based on the average person (see the Normal Curve).

The Unstructured Rep System Is Flawed

The unstructured approach can create these questions:
  • 3 sets of 10 reps with what amount of resistance?
  • Likewise, use a 5 x 5 program but how much resistance for each of the five sets?
  • On which set of a 10-8-6 script will overload occur?
  • What type of intensity should be exuded on each set? All-out on all or only on the last few sets?
  • Should the established rep goals be easy, moderate, or hard to obtain?

The 1 Rep Max System Is Flawed

If you're using the more structured percentage of a 1RM system you can also run into potential flaws. I'll admit it can be useful, but is it truly accurate? Here are some examples. All reps listed are based on the percentage of a 1RM.
  • 5 x 5 at 87%
  • 6 @ 70%, 6 @ 75%, 6 @ 80%, 6 85%
  • 3 x 10 at 75%
  • 12 @ 65%, 10 @ 72%, 8 @ 80%, 6 @ 87%
Due to variations in muscle fiber type (the percentage of slower-to-fatigue and faster-to-fatigue contractile units), bone (lever) length, muscle origin and insertion points, and nervous system ability (motor unit hook-ups within the central nervous system), there is no one size fits all precise means of assigning a specific number of exercise repetitions to an exact percentage of a 1RM. Different results are likely from one person to another.

"If you’re looking for a sound remedy to your out-of-control program, look to the time-proven, but underrated repetition (rep) range as a means of accurate and progressive training."

Take the 5 x 5 at 87% of a 1RM script. Subject one (1RM of 350 pounds) may possess a higher percentage of faster-to-fatigue and stronger type 2 muscle fibers, shorter bone levers, exceptional tendon attachments, and the ability to recruit an average percentage of motor units each repetition. 5 sets of 5 reps with 304.5 pounds (87%) may thus be dead-on and create efficient muscle overload at the 5-rep point.
On the other hand, apply the 5 x 5 at 87% to a subject (1RM of 200 pounds) with a higher percentage of slower-to-fatigue type 1 muscle fibers, average bone levers, average tendon attachments, and an average ability in recruiting motor units. The 5 x 5 at 87% (174 pounds) may lead to a less-than-optimal muscle overload if each set was aborted at five reps. Most likely, this subject could perform more than five reps with 87% of a 1RM. Assume eight reps were possible. Would then stopping at five reps lead to a suboptimal overload? Of course it would.
Then, take 3 x 10 at 75% of a 1RM. One person may only be able to perform ten, nine, and eight reps, respectively. Ironically, if these sets were all performed to volitional muscle fatigue, it would be a positive even though the projected rep goal was not attained. But how would the forthcoming workouts be structured? Would you decrease the 1RM to better comply with the prescribed reps? If so, would that not compromise the accuracy of the 1RM? 
Similarly, say a person could perform more reps with the 75% 1RM (i.e., 14, 13, and 11). Two points. If he or she only performed the prescribed ten reps, would the athlete not be selling him- or herself short? Should the 1RM be readjusted upward for forthcoming workouts to better correspond to the prescribed reps? Again, what would this be saying about his or false 1RM?

"Becoming stronger can be accomplished by either lifting the same amount of resistance for more reps or increasing the amount of resistance for the same number of reps."

Strength Training Facts

We all need simplicity in life, especially when it comes to our diversions such as physical training. Your daily grind in life can be tiresome and stressful in itself. Can we not keep training simple?
Enter the gorgeous, delicious, and soothing rep range. It's a no-brainer for 96% of the training population (the other 4% being the genetic freaks or trash bags on the ends of the aforementioned Normal Curve). But before I lay out the simplicity and virtues of the rep range it is important to know these proven facts:
  • Becoming stronger can be accomplished by either lifting the same amount of resistance for more reps or increasing the amount of resistance for the same number of reps.
  • Strength does not occur in leaps and bounds. It is a slow process. Initially, you become stronger due to learning how to perform an exercise. 
  • Strength and power are related. Increase your strength and your ability to express power will be improved.
Because of the aforementioned genetic variations (fiber type, leverage, nervous system), programs should be tailored to an athlete’s inherent ability. That is, one person may require more exercise sets and another requires fewer. 
One person may require exercise reps in the range of 14 to 20 and another eight to 12. One person may need 48 hours of recovery time between training session and another 72+ hours. Thus, canned programs - that is, those prescribed in muscle magazines - don't fit all trainees. They may offer guidelines, but they are not perfected to you.
strength, 1 rep max, power, strength training, repetition

Rep Range Virtues

  • A variety can be used. 4-8, 6-10, 8-12, 10-14, 12-16, 14-18, 16-20, 20-25, 25-35.
  • Percentages of a 1RM are not required. They account for the different outcomes that haunt the exact percentage of 1RM protocols.
  • Volitional muscular fatigue (as many reps possible within your ability). Rep ranges are an objective assurance you can create optimal overload.
  • Based on your genetics - your muscle fiber type, lever lengths, muscle attachments, and nervous system - you can apply the appropriate rep range for your inherent ability.

Simple Strength Progression

Rep range of 10-14. In workout one, you use 125 pounds and reach volitional muscular fatigue at 12 reps. A thirteenth rep would be impossible, thus overload was created. The next session your goal is more than 12 reps and you get the high end of the range, 14. 
Naturally, you've become stronger. This is the signal to increase the resistance in the forthcoming session with the goal of achieving the minimum of 10 reps. In that session, you get 10 or 11 reps and you are stronger. No argument needed.

Strength, Power, and Muscle Endurance

These are all taken care of when using repetition ranges. Simple training protocols will enhance your ability to recruit more muscle tissue over time. They all lead to improved strength, power, and endurance, all other factors being equal.
Essentially, the rep range tells you exactly what needs to be done. Either do more reps with the same resistance or increase resistance and aim for the bottom end of the range. These progressions guarantee muscle overload, account for different outcomes if an athlete was using the percentage of a 1RM system, and are objective.
Below are examples of workouts that use rep ranges in either single or multiple set scripts (click on each table to enlarge it - the table will open a new window):
Photos courtesy of Strength Education.