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Muscle Growth: Sets & Reps

Muscle Growth: Sets & Reps
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Sets, Reps and Muscle Fibers

Through my years of being involved in the weight training business, being around several great professional and amateur athletes and being a personal trainer for several years, one of the questions that I always get is “How many reps should I do?”.

While this might seem like a hard question to answer, it is not that complicated. Not when you combine some science, some common sense and listen to your body. The idea of weight training is to do two things, make a muscle stronger and, for the bodybuilding world, make the muscle bigger. This happens when you put enough stimulation on the two muscle fibers, fast-twitch and slow-twitch on a progressive and continual basis allowing enough time for recuperation. Sounds simple, right?

Let’s understand the two types of muscle fiber a little more.

SLOW TWITCH MUSCLE FIBERS (Type I): The slow twitch muscle fibers are more efficient at using oxygen to generate more fuel for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch muscle fibers and can go for a long time before they fatigue. Slow twitch fibers are great for endurance. These muscle fibers are typically used more by long distance runners, cyclists and swimmers. The typical rep scheme to stimulate these fibers is 15-20.

FAST TWITCH MUSCLE FIBERS (Type II): The fast twitch muscle fibers use anaerobic metabolism to create fuel, they are better at generating short bursts of strength however they fatigue more quickly. These muscle fibers are typically used more by bodybuilders and powerlifters. The typical rep scheme to stimulate these fibers is 8-12.

To completely stimulate the muscle for growth and size you MUST work both fibers. What is the perfect rep scheme to accomplish this? It would look something like this:

Warm Up: 2 sets of 15 reps
Movement 1: 3-4 sets of 8 reps
Movement 2: 3-4 sets of 12 reps
Movement 3: 3-4 sets of 20 reps

Let’s apply this to a chest workout:
Flat Bench:
– 2 sets of 15 reps (warm up)
– 3-4 sets of 8 reps
Incline Dumbbell Press:
– 3-4 sets of 12 reps
Cable Cross Overs:
– 3-4 sets of 20 reps

A couple of notes:
– Rest 2 minutes between sets for movements one and two.
– Rest 60 seconds between sets when doing movement three.
– Train heavy, because you’re doing 20 reps that does not mean 20 light reps, stay heavy!
– Add resistance to each set. If you can do 8 reps on the first set of movement one, add weight, even if it 2.5lbs, add weight. You should be pushing to get the goal reps.

There are tons of theories about the ideal number of reps that you need to do to get stronger and to grow. Some of them make sense and others, well, not so much. As I said in the beginning, listen to your body. See how it responds. The fun of working out and training is trying new things but a few facts do hold true and one is that you MUST stimulate both muscle fibers for optimal growth.

I love to talk training and nutrition so please feel free to contact me anytime, I answer almost every e-mail myself and am at

Michael A. Carrubba
CEO/Founder Clinical Sports Labs
Team CSLabs

McArdle, W.D., Katch, F.I. & Katch, V.I. (1996). Exercise Physiology: Energy, nutrition and human performance

Jacob Wilson. Muscle Fibers: An In Depth Analysis Part 2

Fredrick Hatfield Ph.D. Hardcore Bodybuilding, A scientific Approach

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