Training hard is easy, but training smart gets you closer to your goals. For example, let’s say you want to build muscle. You can choose a light weight and rep it 50-60 times, or grab a heavier weight and push it maybe 10 times. Both examples are hard, but one method is superior for building muscle.

Effort is important, but it has to be applied correctly. To optimise your effort in the gym, you need to understand which specific rep ranges can best help you reach your goals. Thankfully, researchers have already weighed in on the topic.

Here are the basic rules of choosing the right reps per set for your fitness needs!

1. Training For Muscle Size (Hypertrophy)

If you’re training for muscle size, choose a weight at which you reach muscle failure in the 8-12-rep range. After your warm-up sets—which are never taken to failure—you should select a load with which you can complete at least 8 reps but not more than 12.

That means if you can do only 6-7 reps, the weight is too heavy, so reduce it on subsequent sets. It also means that if you can do more than 12 reps, but simply stop at 12, that’s not a “true” set. A true set is one in which you fail—the point at which you can’t do another rep with good form on your own—within the target rep range of 8-12.

If you can easily do more than 12, add weight on your next set so that you’re failing in the target range. If you’re exercising with poor form, the weight is probably too heavy, regardless of when you’re failing.

Choosing the right load for your muscle-building goal effectively targets the fast-twitch muscle fibres, which are more prone to growing bigger and stronger in response to resistance training, with enough volume to stimulate growth. However, these fibres fatigue fairly quickly, which is why you can’t lift a very heavyweight very many times.

If you’re looking to maximise muscle size, target 8-12 reps per set (on average) and choose multi-joint movements like the bench press, squat, overhead press, bent-over row and deadlift, which recruit more total muscle mass than single-joint moves, thus allowing you to lift heavier weights.

Hit a target muscle from multiple angles with high volume (sets and reps) to stimulate growth. In general, your rest periods should be in the 1- to 2-minute range.

Related article: The No-Nonsense Five Sets Five Reps Routine That Focuses On A Full-Body Strength Workout

2. Training For Strength

While choosing a weight at which you can do just 8-12 reps builds muscle, it also builds strength. But that weight is not optimal for strength building. When focusing on maximising your strength, you want to train with even heavier loads, ones you can lift for just 1-6 reps. These very heavy weights provide the stimulus needed to grow stronger.

Most, don’t train heavy all the time, however. They cycle high-intensity periods (heavy training) with low-intensity periods to save their joints, reduce the risk of injury, and peak at the right time for competition.

Hence, they typically follow a 12- or 16-week periodised programme that gets progressively heavier. That means doing sets of 5 reps, 3, and finally 2 and 1. The strength trainer also targets the fast-twitch fibres. His focus isn’t just on building and strengthening the muscle fibres themselves, but also training the nervous system.

Strength trainers differ from bodybuilders, in that they typically avoid taking sets to muscle failure, which could adversely affect the nervous system. Rest periods between sets for main lifts are fairly long—up to 3-5 minutes—so that incomplete recovery doesn’t inhibit succeeding sets.

After the main multi joint exercise, additional movements are included to strengthen weak links in the execution of the main lift.

Related article: Try These Smart Tweaks To Your Favourite Gym Moves To Reignite Your Upper-Body Muscle-Building Mission

Training For Muscle Endurance

Low-intensity training is typically considered aerobic exercise, since oxygen plays a key role in energy or production. This allows you to maintain your activity level for a longer period of time.

This energy process occurs primarily in slow-twitch muscle fibres, so performing low-intensity, high-repetition training builds up the mechanisms within the muscle cell that make it more aerobically efficient.

This type of training enhances the muscle’s endurance without necessarily increasing the size of the muscle. Highly trained aerobic athletes can do lots of reps for long periods of time without fatiguing.

Focusing on muscle endurance means choosing fairly light weights that can be done for 15-20 reps or more.

Low-weight/high-rep lower-body multi joint exercises and even Olympic lifts can be done to improve muscular endurance, so long as form is never compromised in an effort to keep a set going. Rest periods should be kept fairly short, since oxygen intake and lactic-acid removal shouldn’t be limiting factors as you exercise.

Related article: Weights vs Cardio: Which Burns More Fat? Your Guide to the Perfect Body

The Relationship Between Reps And Weight

Discovering how many reps you should do also tells you how much weight you should lift. The two are inseparably linked. If you were to plot a graph, you’d discover a near-linear inverse relationship between the two: add more weight and you can do fewer reps; with a lighter weight, you can do more reps.

You don’t need to train in one rep range all the time. You might start a workout with a heavy compound exercise for 5 sets of 5 reps. To focus on building muscle, you could follow that with a few exercises in the 8-12 range. To finish the workout, you could even tap into your slow-twitch reserves and finish the session with an isolation exercise in the 15-20 range.

With time, you’ll understand your personal strength curve and the relationship of weight to reps for each exercise you do. When building muscle, once you can do more than about 12 reps on a core lift, it’s time to increase the resistance by about 5-10 percent.

The weight you choose along your strength curve should correspond to the number of reps you want to achieve, which matches your training goals. In that sense, your workouts should never be random, where you just grab any old weight; there is a best weight and optimal number of reps you should be doing.