What Are Reps and Sets, and Why Are They So Important?

When you're new to working out, it may feel like you're hearing a whole new language. After all, you probably haven't heard much about reps and sets in the office or at the supermarket.

But sets and reps will quickly become part of your vocabulary. These concepts help you organize and structure any exercise routine and can help you track your progress.

"Reps" is short for repetitions, or the number of times you perform any given exercise in your workout. If a fitness instructor, personal trainer or an online training plan tells you to do 10 reps of body-weight squats, that means you'll repeat the exercise 10 times.

Each rep of an exercise puts your muscles through a few positions, including a lengthening phase, a contraction phase and a shortening phase, according to the American Council on Exercise (ACE).

The different muscle positions of each rep is easy to visualize with a biceps curl. As you raise a dumbbell up to your shoulder, your biceps shortens and contracts. Then, as you lower the weight down, the muscle lengthens. All of this action happens in just one repetition.

Most exercises are performed in a range of 8 to 12 reps total per set (more on sets below). This range is best for general increase in muscle strength and size (aka hypertrophy), according to the ACE.

On the other hand, to build muscular endurance, you'll want to keep your reps high — between 20 to 30 repetitions, according to the ACE. Higher rep ranges are excellent for runners or cyclists, who need to perform repetitive motions for long periods of time without muscle fatigue.

Generally, the amount of repetitions you perform should be inversely related to the weight you're lifting, the ACE recommends. If you're performing heavy squats, for instance, you may want to do just 6 reps. On the other hand, if you're doing light hammer curls, you can go for 12 reps.

Whether you're training for hypertrophy or muscular endurance, you want to perform your reps to a point of muscular fatigue, which is when you feel too tired to do one more repetition with good form.

That number will be different for everyone, Carolina Araujo, certified personal trainer, tells LIVESTRONG.com. For some people that's 10 reps, while for others it's 15.

The term "sets" tells you how many times you will repeat a particular number of repetitions of a given exercise. Let's say you're doing triceps kickbacks. Two sets of 15 reps means you'll perform 15 kickbacks two times total, resting between each round. In total, you'll be doing 30 kickbacks.

As with the number of reps you do, you can also tailor your sets to your fitness goals. Araujo suggests performing each exercise for about 3 to 4 sets if you're looking to improve your body composition. To build muscular endurance, you can go up to 5 sets, she says.

No matter your goals, you want to keep your sets manageable, just like with your reps. Perform enough sets to fatigue your muscles, but make sure to prioritize good form over the amount of sets and exercises you do.

This depends on your fitness goal(s). Those looking to shed fat should focus on higher reps per set. Those looking to increase muscle strength or size should focus on more sets with lower reps per set.

Both your sets and reps are important when building any kind of strength, according to Araujo. But when it comes to functional strength, you want to focus a little more on your reps.

"A lot of functional strength requires building muscular endurance," she says. "Doing an exercise for many reps is the way to do that."

So, when it comes to increasing functional strength, you want to do a higher number of reps (with good form, of course) and a moderate number of sets (think 12 to 15 reps for 3 to 4 sets) of each exercise.

For building muscle, you definitely want to focus more on your sets and the overall quality of each rep, Araujo says. In other words, you want to keep your reps low (6 to 8 reps per set) and do each one with good form, focusing on contracting (squeezing) the muscles you're working.

"Let's say you're doing squats and want to build lower-body muscles," she says. "With each squat, focus on controlling the weight, getting to 90 degrees and squeezing your glutes on the way up."

You don't need a ​ton​ of sets to build muscle, either. Anywhere between 4 and 6 sets per exercise should do the trick. Again, the focus is on lifting heavy with good form, not the specific number of sets and reps.

Both your sets and reps matter if you want to build overall fitness and improve your health, Araujo says. But your starting point can help you decide which takes a little more priority.

"For those who want to shed a little fat to improve their overall fitness and health, higher reps is more beneficial," she says. "But for those who are looking to increase their overall muscle mass, lower reps with moderate sets is best."

It all comes back to your goals. And when it comes to improving your general health, doing strength-training workouts a few times each week is already a huge first step in the right direction.

Sets and reps provide organization and structure to your workout. Along with the amount of weight you lift, these elements make up your overall training volume.

Week to week, you can tweak these elements to create progressive overload, which is the process of gradually intensifying your workouts (by adding more sets, reps or weight) to build muscle mass, strength and endurance.

As you progress your training regimen, avoid ramping up the sets or reps too quickly. A little soreness post-workout is normal, especially if you're trying new exercises. But if you increase your training volume too aggressively, you may experience some serious soreness and even run the risk of overtraining or getting injured.

Instead, increase your weight, sets and/or reps little by little and monitor how your body feels each day. While your ego may drive you to stack on as much weight as possible, Araujo says, always prioritize your form to stay safe while training.