How Many Reps Should I Do?
For as long as I can remember there has been confusion over how many reps (or repetitions) you should do for each exercise. Why is this important? We program exercises in a training program based on how many repetitions we expect you to be able to complete with each set. It is THE guide to deciding how much resistance you will use on each exercise and is a strong determinant of the results you will experience from training. The confusion is understandable to an extent because there are a lot of variables to consider. Here is a primer to help you better comprehend the why behind your program.
First, what is a repetition? A repetition refers to one complete full range of motion of a particular movement or exercise. Depending on who you’re talking to you might learn the ideal number of repetitions is anywhere between 1 and 100.
This is most likely because there is a significant bias associated with how people feel about this topic. The majority of “professionals” in the fitness industry are still more likely to base their opinions on what has worked for them personally over what the science has confirmed or denied to date. For example, if you talk to a powerlifter you might be told 1-6 reps are ideal; an endurance athlete might tell you 15-25; whereas someone with a bodybuilding background is likely to tell you 8-15 is the answer.
The American College of Sports Medicine recommends 8-12 repetitions per exercise for healthy adults, and 10-15 repetitions for those who are elderly or frail. Although this can be a good guideline for most people, it is an oversimplification and is based solely on the goal of maintaining good health.
Here are some things we consider when determining how many repetitions we recommend.
The number of repetitions depend on the goal.
In general, repetition selection occurs on a continuum with one (1) representing absolute strength, and 100 representing pure stamina or endurance.
If you are an strength/power athlete, you will optimize your training by moving a light to moderate weight quickly for 1-6 repetitions to improve power, and build absolute strength by moving as much weight as possible for 1-3 repetitions.
If you are looking for body composition change (weight loss included), you will optimize your training by moving a moderate weight at a controlled pace for somewhere between 5 and 25 repetitions. Science has revealed that muscles will grow at virtually any repetition range. The catch here is, as the repetitions get higher (with a lighter weight), you have to achieve muscle failure to a greater extent compared to when you use a moderate weight and moderate number of repetitions.
If you’re an endurance athlete, you will optimize your training by moving a light to moderate weight over 15-25 repetitions. In this case, the sport already challenges their muscles to improve stamina. Using higher repetitions can be useless because they need to balance their training.
If you’re training for LIFE, you want to have a good mix of exercises that incorporate a wide variety of repetition ranges to challenge a variety of muscle characteristics.
Some muscles are designed for endurance, whereas other muscles are designed for strength.
The muscles in your body can be described as either TONIC or PHASIC. The tonic muscles are typically “on” most of the time, have higher tone and are mostly responsible for posture. The phasic muscles are designed to turn on and off on demand and are thus responsible for gross movement. This concept was suggested in the 1960s by Vladimir Janda.
Tonic muscles are designed for stamina. To improve them we need to challenge them with higher repetitions (light to moderate weight) or extended isometric contractions. They will respond best to 15-25 or more repetitions or 45-60” or more of sustained effort. Think of the muscles between your shoulder blades, your “core”, the small muscles around your hips, or even your lower leg muscles that have kept you upright if you stand all day.
Phasic muscles are designed for strength/power. To improve them we need to challenge them with lower repetitions (moderate to heavy weight), or fast/explosive contractions. They will respond best to 1-15 repetitions at controlled moderate to explosively fast speeds. Think of the larger muscles of your Chest, Back, Arms and Legs.
Some people have a predominance of endurance-type muscle fibers, whereas other people have a predominance of fibers designed for strength and power.
Most of us fall into the “average” range and therefore have a relatively even distribution of muscle fibers along the continuum. In this case, using a variety of repetition ranges throughout a workout would be desirable.
If, however, you were an Olympic-level marathoner you might have more endurance-type muscle fibers, up to 90% in fact. In this situation, training with higher repetitions is essential to provide the right stimulus, which using lower repetitions (higher weight) could actually be detrimental.
The reverse is true for a Power Lifter who can possess up to 70% strength/power-type muscle fibers. In this case, using lower repetitions (higher weight) would be ideal, and higher repetitions may be detrimental. This is also the case for most team sports athletes looking for performance improvement.
An interesting fact is that some muscle fibers can convert from strength/power-type to endurance-type if higher repetitions (moderate weights) are predominantly used during training. Although it can happen the other way around, its not as likely or substantial. This explains the detriment to someone who has a gift for strength/explosiveness and consequently performance goals.
Some movements are highly technical, while others are quite simple. Choosing the wrong number of repetitions in this case could get you injured.
Highly technical or multi-joint exercises, such as the Deadlift, can become increasingly risky at high repetitions especially when moderate to high resistances are used. To get better at a technical movement requires perfect practice. You must be in control over the movement pattern (which is complex), your breathing, and the tension in your muscles to safely perform this exercise. Fatigue, which occurs more specifically with higher repetitions, will result in the inability to be in control. If this happens, form breaks down, movement improvements become compromised, and injury risk increases with each subsequent repetition. Squats, Bench Presses, Pull-Ups, Lunges, Jumps all fall into this category as well. For these exercises, we prefer to select a low to moderate number of repetitions in most cases, especially when the resistance is moderate to heavy.
Isolation exercises, or single joint movements on the other hand are very simple and are quite difficult to injure yourself. Triceps press-downs, Biceps curls, Knee Extensions, Hamstring Curls, Calf Raises are all single joint exercises. Although they work phasic muscles, they can often be safely performed with higher numbers of repetitions to failure. We often prefer to use higher repetitions (lower weight) with exercises such as the Knee Extension because there is less compression on the knee joint with lighter weight.
Categorizing exercises in this way is quite practical for those of us training for life. We want to train exercises that help us improve how we move. The most important variable in this case is understanding that “perfect practice makes perfect”. We then must be conscious to perform our complex movements well (i.e. with lower repetitions), and know that we can use isolation exercises to supplement our need to feel the “burn” or effort during a workout.
As you can see, there is a good reason why many people are confused over the question of how many repetitions you should do, even amongst fitness professionals. After 25 years in the industry I’m still learning how to adapt our programs based on what we know about the body and its response to various training strategies. Next time you pick up your program see if you can identify some of the variables mentioned here. If you have questions, ask one of our coaches.