High Reps vs Low Reps for Muscle Growth: What Works Best?

Do your clients want to increase their muscle mass?

The many benefits associated with muscle hypertrophy (aka muscle growth) are likely at the top of the list of goals for many of your clients. Increased muscle mass or muscle growth has numerous benefits (i.e., improvements in body composition, increased calorie burn, improvements in muscle symmetry, bone health, overall physical appearance, and athletic performance, etc.). So, it’s no wonder that building muscle mass is a common goal for so many.

So, what’s the best way to help them with their hypertrophy goals—should clients use lower reps or higher reps to stimulate muscle growth?

The Training Principles

Before we dive into the science of muscle hypertrophy, it’s important to know there are several important principles that help fitness professionals understand how and why the body adapts to exercise. The following list is not all-inclusive of every training principle but those listed below are essential for personal trainers to understand and use as they develop hypertrophy programs for clients.

Principle of Individual Differences

This principle is critical to your success as a trainer and something you will need to incorporate regardless of your client’s goals. The principle explains that each client is unique, so the way their body responds, their genetics, and their individual needs and limitations will vary. This means that there is NOT one way to train ALL clients. So, the hypertrophy program you design for each client should be unique to that client.

Progressive Overload Principle

The overload principle states that you need to challenge the body, muscle, body system, etc., with a stress that is GREATER than the stress that it is used to. So, that could mean a faster pace, more weight, less rest time, more repetitions (reps), etc. Done correctly, this overload is ultimately what is going to force the body system (or muscle) to adapt. The great thing about this principle is that it helps us understand that stress can be good. The human body needs stress to change and adapt. However, determining what type of stress will create the appropriate adaptation of muscle growth (aka hypertrophy) and allowing for proper rest and recovery are most critical when applying this principle.

Periodization

One might think that because of the principle of progressive overload an exercise program should continually get harder (increase in weight, faster times, etc.). That’s only partly true. A personal trainer should continue to progress clients, but, as we mentioned previously, incorporating rest and recovery, so the body can repair, is critical. Phases of structured rest and recovery or lighter training will allow the body to adapt to the stress and prevent overtraining. This is why periodization is so important. A periodized training program cycles through phases where the acute variables (rest, reps, intensity, etc.) are manipulated to allow for periods of both stress and recovery.

Acute Training Variables

In addition to the training principles, there are several acute variables that can be manipulated during training to elicit different results. These variables are an intricate part of designing an individualized training program aligned with a client’s goals. Let’s explore a few of them:

1. Intensity: training intensity is the amount of load lifted—often represented as a percentage of an individual’s 1RM (one rep max or, in other words, the maximum weight that an individual can lift for 1 repetition).

2. Volume: the volume of training is the number of repetitions multiplied by the number of sets in a workout. This can also be further multiplied by the number of workouts per week.

3. Rest: a variable that is often forgotten about or overlooked variable, is the amount of time given between each set to allow the body to recover.

4. Time under tension/tempo: is the speed of the exercise (i.e. the combination of the time it takes for each phase of the lift—concentric, isometric, and eccentric).

Each of these variables is critical in designing a proper program for clients. And not just programs designed for building muscle mass, these variables are critical for all types of training programs.

The Science of Hypertrophy

So, based on the training principles, technically, if the muscle is stressed beyond what it is used to then it should grow, right?

It depends. Keep in mind, building muscle mass or changes to the size of the muscle aren’t the only adaption that can occur with weight training. Different types of training can increase capillary networks around the muscle fiber, increase resistance to fatigue (improved muscular endurance), increase mitochondria (better energy production), increase strength or power, etc. This is why it’s so important to use the training variables properly, individualize each client’s program, and train them in alignment with their goals so their body responds the way they want it to.

So, that still leaves us with the question – should clients use lower reps or higher reps for hypertrophy?

Although there is still some conflicting research around building muscle mass, historically, many fitness professionals were in agreement with the science that said heavy weights with a moderate rep range is ideal for muscle growth (typically around 8-12 repetitions). This is often paired with the specific ranges for the following acute variables:

• Sets: 3-6

• Intensity: 60-80% 1 Rep Maximum (1RM)

• Rest: 60 seconds (1)(2)

However, recent research has suggested that there may be more variance in the ranges and load with regard to the muscle adaptation of hypertrophy. These studies evaluated reps completed until failure with higher reps and lower weight compared to higher weight and lower reps and found that both had similar results regarding hypertrophy (3)(4)(5).

So, what’s the answer?

Based on the research, technically, both or either low and high reps may be ideal in building muscle. The key is to ensure muscle “failure” is reached or, in other words, the point where the muscle can no longer execute the movement (5)(6). Lifting weights until muscle failure helps ensure that the number of muscle fibers recruited is maximized.

One thing a trainer may want to consider when designing a weight training program for increasing muscle mass is whether or not the client has any other goals in addition to hypertrophy. Do they also want to see increases in their muscular strength? If so, lower reps and heavier weight may be ideal. Do they also want to build muscular endurance? If that’s the case, a higher rep range may be the better option (3)(7). The other variable to consider is the client's time—higher rep ranges to muscle failure will likely require more time.

That being said, it’s important to remember that hypertrophy isn’t a result of executing just one training session with the specific acute variables. Changes to the muscle size (and body) will occur from a collection of the appropriate training variables over a period of several weeks (i.e. their training volume). In addition, adequate rest and recovery, proper nutrition, proper form, etc. are critical components of hypertrophy training. So, ultimately, it’s more than just a rep range that helps your clients achieve the muscle mass they’re after.

Interested in learning more about how to increase muscle mass, how the body adapts to weight training, and how to design individualized programs for different goals? ISSA’s Certified Personal Training Course is perfect for you!! Sign up today and you can complete the entire course at your pace, from the comfort of your home!