You’ve undoubtedly heard the standard gym myth that training for size or strength requires using heavy weights for just a few reps, while training to improve muscle definition requires using lighter weights for a high number of repetitions. While there is some degree of truth to these claims, it is important to understand that the number of reps you do for each exercise has a significant influence on the results you get from your workout program.

Today, many popular programs encourage participants to do high numbers of reps for ballistic exercises, such as barbell cleans or jumps. Unfortunately, doing too many reps may actually cause injury and limit your ability to train. To make sure you’re maximizing the efficiency of your time in the gym, here are seven things to consider when determining how many repetitions you should do based on your personal fitness goals.

1. A repetition is a single, individual action of the muscles responsible for creating movement at a joint or series of joints. Each repetition involves three specific phases of muscle action: lengthening, a momentary pause and shortening.

2. Regardless of your specific fitness goals, the number of repetitions you do is not nearly as important as whether those repetitions are performed to a moment of muscular fatigue. Achieving fatigue in a muscle means that it is not capable of performing one more rep and ensures that all of the muscle fibers responsible for moving that muscle have been engaged. If your goal is to improve definition and you feel capable of performing a few more reps at the end of a given set, you have not fatigued all of the type II fibers that are responsible for creating definition. This means you have wasted your time because you will not be training in the most efficient manner possible for your goal.

3. In general, the number of reps you do for an exercise is inversely related to the amount of weight you use. As the amount of weight goes up, the number of repetitions you are able to perform decreases. Therefore, higher-intensity loads can only be performed for a few repetitions, while lower-intensity loads can be moved for a relatively high number of repetitions before fatigue sets in.

4. Training for strength requires using heavier loads, which subsequently limits the number of reps that can be performed. A heavier weight will automatically recruit more type II fibers in the involved muscles. Type II fibers rely on anaerobic metabolism, which provides only a limited amount of energy. This is another reason why heavy weights can only be moved for a few reps at a time—the muscle simply runs out of available energy. If your goal is to improve strength, use weights that cause fatigue after no more than six repetitions.  

5. Training for definition can be achieved by a couple of different rep ranges. The number of reps isn’t as important as the length of time during which the muscle stays under tension. The type II fibers responsible for strength are also responsible for creating the appearance of muscle definition. Definition comes from a muscle maintaining a state of semi-contraction, which is achieved by keeping a muscle under tension for a longer period of time. A higher numbers of reps performed at a slower movement speed can facilitate the tension needed to increase definition. No matter how many reps you decide to use, to achieve definition you must reach a state of momentary fatigue, which means you’re not capable of performing another rep.

6. If you are a runner, cyclist, swimmer or other type of endurance athlete, you are probably more interested in using strength training to support the specific training necessary to achieve success in your sport. In this case, your strength-training program should focus on activating the type I muscle fibers that rely on aerobic metabolism, which requires performing as many as 20 or 30 reps. Endurance athletes need to be as aerobically efficient as possible, so performing strength-training exercises with light weights for a high number of reps will help muscles develop the mitochondrial density and aerobic efficiency necessary to support endurance-training efforts. In this case, working until fatigue is not necessary, because you’re not trying to add muscle mass; in fact, you want to avoid working to fatigue. However, your rest intervals should be kept relatively short to ensure that your workout creates the necessary stimulus to engage your aerobic metabolism.

7. Power, which is the ability to generate a significant amount of muscle force in the shortest amount of time possible, is a skill that requires specific programming to achieve. Power training can provide a number of important benefits and is completely safe if the appropriate number of reps is used. However, thanks to the popularity of high-intensity workout programs, it is often performed in an unsafe manner. Training for muscular power places tremendous metabolic and mechanical demands on muscle tissue and can rapidly fatigue the nervous system responsible for maintaining proper joint mechanics. When doing technical power-based lifts like the barbell snatch, clean-and-jerk, push press or hang clean, the focus should be on the quality of movement and not the quantity of reps performed. For safe, effective power training, the rep range should focus on the maximum force output for one or two reps and be limited to no more than four or five. The same is true for medicine ball throws or jumps—the emphasis should be on the quality of movement and not the number of repetitions performed. Jumps and throws should focus on technique and be performed for no more than six to eight reps at a time; doing more reps could cause fatigue, which significantly increases the risk of injury. Like endurance training, the goal of power training is NOT to go to fatigue, but to do the assigned number of reps with the best form possible.

Recommended Rep Ranges to Achieve Specific Goals