If you’ve been training for some time now, you may have heard about the two types of muscle growth, sarcoplasmic and myofibrillar. As you may or may not know, there are also two types of muscle fibers: type I and type II. How does this play into rep ranges and muscle growth? Simple: different rep ranges affect these two types of muscle growth and muscle fibers. Let’s see what research has to say about the best rep ranges for muscle growth.
Sarcoplasmic & Myofibrillar Hypertrophy
First of all, let’s break down the two types of muscular hypertrophy. First we have Sarcoplasmic hypertrophy. Breaking down the word, sarco means flesh, and plasmic means plasma. This kind of hypertrophy increases the volume of non-contractile parts of muscle, which includes water, glycogen, collagen, etc.
Myofibrillar hypertrophy on the other hand is broken down like this: Myo means muscle and fibril is a fiber (or thread-like structure). So basically, muscle fiber. When we talk about Myofibrillar hypertrophy, we’re talking about actual increase in size and shape of the contractile muscle fibers. Now, how can we apply this to our training? Simple: research shows that the majority of muscle growth comes from myofibrillar hypertrophy, while the rest comes through sarcoplasmic hypertrophy. Let’s take a look at the two types of muscle fibers in order to see how we can apply this to our training.
Type I & Type II Muscle Fibers
Next, let’s take a look at the two different types of muscle fibers. Type I fibers are also known as “slow-twitch” fibers and have been shown to be more resistant to fatigue. They’ve also been shown to have the least amount of potential for growth and strength output.
Type II fibers on the other hand are known as “fast-twitch” fibers, and also grow and contract faster than their type I counterparts. They also have a higher potential for strength output and growth, but the downside is that they fatigue much faster.
How Does This Fit Into Rep Ranges?
Simple: Research shows that high reps and low loads are effective in targeting Type I fibers, while higher loads and low reps contribute to Type II growth. High volume, low intensity groups compared to High intensity, low volume groups gained less muscle overall because they stimulated more Type I fibers compared to Type II fibers. 3 to 5 reps stimulated more muscle growth than the 10 to 12 rep range in the study below, but I can guarantee if you look at several studies of how muscle growth works, you’ll find many conflicting answers. Ultimately, it comes down to this:
1. Focus on lifting heavy weights in your workouts (when I say heavy, I mean anywhere between 4-8 reps).
2. Do compound movements (squat, bench, deadlift, overhead press).
3. Get stronger over time (Progressive Tension Overload).
Rep Range Recommendations
As a natural weightlifter, your main goal is to get stronger. If you’re doing more than twenty reps per set on squats, then it’s going to be far more difficult to gain strength, although you will develop more Type I fibers (which don’t grow very well, as you know).
What I’d personally recommend is a happy medium of 6 to 8 reps or 4 to 6. When you hit the top of your rep range, move up in weight until you’re able to do so again. Include some higher rep work in your workouts for endurance training and that sarcoplasmic hypertrophy, but mainly focus on your Myofibrillar hypertrophy with your lower rep training.
Take Home Message
You’ll often see plenty of bodybuilders working in much higher rep ranges. This works if you’re taking steroids, due to more volume of fluid in the muscles from sarcoplasmic hypertrophy. Don’t overcomplicate things: get stronger over time, get your total weekly volume right, and you’ll be doing just fine. As always, stay strong.