Do you want to get stronger or build muscle? Have you been lifting weights for months but haven’t seen any changes? While there are a few things that could be preventing you from making gains, one of the most common mistakes people make (especially beginners) is not working out at a high enough intensity.
Choosing the right intensity for an exercise may be one of the trickiest parts of following a training program, but it’s also one of the most important. For resistance exercise, intensity means the amount of resistance the muscles need to overcome to perform a movement. For barbell exercises, that would be the weight of the barbell plus the weight plates loaded onto it. In the case of bodyweight exercises, it’s the amount of the body’s mass that is being moved.
You can change the amount of your body’s weight that you have to move during a bodyweight exercise by changing the position of your limbs. For example, an incline push up (hands elevated) requires the muscles to move less weight than a floor push up, which requires still less weight than a decline push up (feet elevated). You can also add external resistance, for example by performing pull ups with a weight hanging from your waist.
How Do You Measure Intensity in Resistance Training
In sports science research and athletic training programs, intensity is often expressed as a percentage of “1RM” which stands for 1 repetition maximum. That’s the maximum amount of weight that can be lifted during a particular exercise, with good form, for only one repetition. In other words, lifting your 1RM means using a weight heavy enough that you can complete 1 rep, but if you tried to do a second rep you wouldn’t be able to. Once 1RM has been determined (by a 1RM test), a percentage of that maximal weight is prescribed for each exercise in a session. For example, an athlete’s program might say: Bench Press – 4 sets at 80% of 1RM. If that athlete’s bench press 1RM is 200 lbs, they would lift 160 lbs in each set.
The higher the percentage of 1RM, the fewer repetitions can be performed, with the pattern generally fitting the following table (adapted from Haff and Triplett, 2016), although those numbers vary somewhat depending on the individual, their training experience, and the specific exercise being performed.
It’s been found that to increase strength and muscle size, beginners (people with little or no resistance training experience) should be lifting at least 60-70% of their 1RM. Experienced lifters (who have at least 6-12 months of weight training experience) should be lifting at least 70-80% of their 1RM (Kraemer and Ratamess, 2004).
Most People Don’t Select Heavy Enough Weights
A few research studies have tested whether the average person chooses weights that meet the guidelines for resistance training. Unfortunately, many people lift weights that are too light for them to make meaningful increases in their strength or muscle size.
Glass and Stanton (2004) had 13 men and 17 women with no resistance training experience choose their own resistance for 5 different exercises (bench press, leg press, seated row, shoulder press, and bicep curl). They were allowed to perform as many repetitions as they wanted, with the instruction that they should “choose a load that you feel will be sufﬁcient to improve your muscular strength”. They selected weights that were an average of 42-57% of their 1RM, and performed between 10 and 25 repetitions, depending on the exercise.
Focht (2007) had 19 women with no resistance training experience choose their own resistance to perform 10 reps on the chest press, leg extension, lat pulldown, and shoulder press. Those participants selected weights that were an average of 56% of their 1RM.
Dias et al., (2016) had 12 men and 9 women with at least 12 months of resistance training experience select their own resistance to perform 10 reps on the leg press, bench press, leg extension, and bicep curl. They selected an average of 42-62% of their 1RM.
The average participant in each of those studies didn’t select resistance that was heavy enough to improve their strength or muscle mass. If those exercisers were training to get stronger or build muscle, they probably wouldn’t get results because they’re lifting too light, and that lack of improvement might leave them disappointed and less likely to stick to their program.
If you want to increase your strength and muscle mass, it’s important to lift weights that are heavy enough to force your body to adapt. Many exercisers (especially women) are scared off by the idea of lifting heavy, but “heavy” is relative to you. Lifting heavy doesn’t necessarily mean lifting like the guy in the picture below, it just means choosing weights that are challenging for you.
How to Choose Intensity
While the 1RM percentage system is commonly used in research and with athletes, I don’t recommend it for prescribing training intensity for the average exerciser, for several reasons:
- To determine your 1RM you need a 1RM test, which isn’t practical for most people. A 1RM test requires a trained tester and spotter, equipment, and time to administer the test. The person being tested also needs to have good lifting technique. Trying to lift the absolute maximum amount of weight is extremely difficult. Many new lifters aren’t physically or mentally prepared for such a strenuous test.
- 1RM will change during the course of training as the person becomes stronger, so it requires regular re-testing.
- Performance on any given day is dependent on a variety of factors, including recent dietary intake, amount of sleep the previous night, mood state, etc. Restricting weight to a specific percentage of 1RM doesn’t allow for these variations, so a weight that’s appropriate one day may be slightly too heavy or too light the next.
Instead, I recommend using repetition ranges to prescribe intensity. For example, a program might say that you should be performing 3 sets of 8-12 squats. In that case, you should start by determining the amount of weight that you can lift for 8 reps, using the method I described here. It’s important to make sure you’re lifting as heavy as you can for that number of repetitions. In this example, that means you should choose a weight that only allows you to perform 8 repetitions, but if you tried a ninth rep you would fail. That’s also known as an 8RM, or 8 repetition maximum. It’s the maximum part that’s important here. Choosing a weight that challenges you within whatever repetition range you’re working in is the key to getting results.
How Many Repetitions Should You Perform?
The optimal intensity (number of repetitions) you should perform depends on your training experience and your goals.
When first starting out with resistance training, 10-15 repetitions are appropriate for most people. Your primary goal when beginning a training program should be to master good form and develop quality movement for each exercise. You don’t need very heavy weights for that. In fact, lifting weights that are too heavy while trying to learn a proper movement pattern will make the task much more difficult. Also, along with your muscles, your bones, tendons, and ligaments need to be strong enough to handle the resistance. They will adapt and get stronger just like your muscles will, but they need time and gradual progression. Lifting too heavy too soon increases your risk of injury. Start light and progress gradually as you get more familiar with resistance training.
Once you’ve been training consistently for at least several months and are able to perform your exercises with good form, you should choose your repetition ranges based on your fitness goal.
For maximal strength: perform your main lifts with a resistance that only allows you to complete 2-6 repetitions.
For muscle size: you should be lifting weight that only allows you to do 8-12 repetitions.
For muscular endurance: you should be lifting weight that only allows you to do 12-20 repetitions.
Keep in mind that those repetition ranges are just guides. They generally work for most people, but each individual’s response will be different. Some people will respond better to certain rep ranges than others. It’s important to monitor your response to training over time and be willing to make adjustments. You don’t have to stay exclusively within a certain rep range, it’s a good idea to work in a different rep range every once in a while.
Effort and Progress Should be Your Main Priority
If you don’t prioritize effort and progression, it won’t matter what repetition range you choose because you won’t place enough stress on your body to force it to adapt. That means you have to push yourself on each exercise, in every set and repetition you perform.
Let’s say your goal is to increase muscle size, so on your squat exercise you decide to lift in the 8-12 repetition range. However, you choose a weight that’s too light; one that you could actually lift for about 15 reps, but you stop at 10 reps. Your muscles can already handle that much weight for that many repetitions, so there’s no reason for them to get any bigger or stronger.
Lifting heavy weight isn’t easy, it requires a lot of effort, but it’s necessary to increase strength and build muscle. It’s important to learn how to lift heavy weight and to develop the ability to challenge yourself.
Many people think they can’t handle a particular weight when in fact they can, or they stop their set too early because they think they’re getting close to fatigue when they really could have done several more quality repetitions. I’ve trained a lot of people who don’t realize how strong they are and are surprised by how much weight they can actually lift. A good trainer or at least a training partner who knows how to act as a spotter is important here, they can provide a physical and mental safety net and allow you to push a little harder.
I know this can be a complicated aspect of resistance training, so here’s a simple take-away message:
If you’re a beginner, focus on learning good form and quality movement for each exercise you do. Choose a weight that you can lift for 10-15 repetitions. Start slowly and progress gradually over time.
Once you have some training experience, pick a weight for each exercise that only allows you to do the prescribed number of reps with good form: 2-6 reps for maximal strength, 8-12 reps for muscle mass, 12-20 reps for muscular endurance.
Aim to do a little more in each session and you’ll make improvements!