The science behind low rep sets for hypertrophy

Why I think low rep sets are best for hypertrophy We all learned hypertrophy is 8-12 reps per set. But I have grown to strongly oppose that mindset. Below is a detailed explanation. Type I Fibers

For these concepts discussed in this email, it's important to notes these theories should be applied and considered using compound exercises (bench press, squat etc) not single joint exercises (bicep curls, lateral raises etc). Understanding some basics of fiber type is the first step to really understand these concepts. There are Type I fibers which are considered your slow twitch fibers. These fibers are endurance-oriented, fatigue-resistant and activate lower force demands. They are built for sustained, low intensity efforts such as jogging and high rep/light weight lifting. We will get into some semantics in a second, but that's the summary of Type I fibers

Type II Fibers

These are your fast twitch fibers that generate high force and power but fatigue quickly. These fibers are split into sub categories

+Type IIa: Moderately fatigue-resistant, good for strength and moderate-duration efforts

+Type IIx: Great for maximal force production and they are recruited for explosive or very heavy lifts, but tire the fastest.

How Fiber Recruitment Works

Muscle fibers are recruited based on the size principle. The size principle states: Motor units are activated in order of size from smallest to largest depending on the force required. This is why with light loads, type I fibers are tapped first. Within a higher rep set of lighter weight force demands increase as fatigue sets in which then leads to the recruitment of type IIa. Type IIx activation is minimal unless you reach absolute failure and even then it's less than with heavy loads. Semantically people can argue that sets to failure activate type IIa and type IIx but it's like saying you eat peanut butter as a source of protein. Yea peanut butter has some protein but it's more of a source of fat and not the best option if you're looking for a high protein source. Important point I always make here, the higher rep sets are depending on fatigue to get to the type IIa motor units. Ultimately fatigue is what limits recruitment and in a set of 10, the last 3 reps might activate type II fibers but the first 7 are wasted energy IMO.

The hack is to "jump the fence" on the type I fibers and get straight to type IIa and type IIx fibers. Maximal or near-maximal loads (as well as explosive moves) recruit type IIx.

Low-rep, heavy sets hit the threshold for BOTH type IIa and type IIx are needed RIGHT AWAY because the load exceeds what type I fibers can handle alone.

Supported by Research

EMG studies from the Journal of Applied Physiology show greater Type II activation with loads above 70%. Studies like those from Campos et al. (2002) show that heavy resistance training (3-5 reps, 80-90% 1RM) increases type II fiber size and strength more than moderate/high-rep protocols. Higher rep boosts Type I and IIa size but less so for IIx. Here are some more studies that support these findings

+Campos et al. (2002) in European Journal of Applied Physiology-low reps win for power

+Fry et al. (2003). Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters. Journal of Strength and Conditioning Reseach, 17(4) 746-754

+ Ruple et al. (2021). Myofibril and mitochondrial area changes in type I and II fibers following 10 weeks of resistance training in previously untrained men. Frontiers in Physiology, 12, 728683

What you can Takeaway

For type II fiber activation (and myofibril hypertrophy), low-rep, heavy sets are king. They target the fast-twitch fibers directly and efficiently. Directly and efficiently, those are the key words there that matter most to me. Higher rep sets with lighter loads can still hit type IIa with the reps near failure but that are much less effective at maximizing type IIx as well as strength.

If you are looking for the next edge in your training, this is it. Be sure that you are utilizing these principles into your compound training, 2-3 exercises per session for sets of 5 or less. There are MANY ways to do it and I actively create programs on a weekly basis to meet clients and athletes where they are at and guide them towards lower rep sets. This is highly dependent of the person's goals and needs, but I have a ton of programming options you can shop by clicking the button below. The king of the low rep set programs you'll see is Super Sets, and Powerlifting program, and a lot of my Adult Strength and Fitness programs have lower rep sets sprinkled throughout the program. Again it will depend on the person's abilities and goals, but check out the programs and start a FREE 10 day trial today!

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