The Art of Muscle Fiber Recruitment
- Jake Hicks
- Aug 13
- 7 min read
You can't study this. You have to feel it. I don't care what a book says, until you feel it you cannot possibly understand the art of motor unit recruitment. I will lay it out for you like I'm explaining it to a 10 year old
It feels taboo to give my opinions on this topic, I'm gonna do it anyway. I'll break down a concept I think doesn’t get talked about enough: how your nervous system chooses which muscle fibers to use and how you can manipulate that choice to get stronger, bigger, and faster. I want to explain it like I’m talking to my ten- or eleven-year-old nephew—simple, practical, and usable—because the principle is straightforward, but the application is where most people get confused.
To watch the video version of this topic on YouTube CLICK HERE
Why motor unit recruitment matters
When you lift, you don’t use every muscle fiber in a muscle all the time. Muscles are made of many fibers, and your body recruits them based on need. If your goal is maximal strength, hypertrophy, or speed, you want to recruit as many fibers (motor units) as possible—especially the big, powerful ones. Doesn't matter if you're looking to get stronger, bigger or faster, each requires you to produce your max force outputs. The difference is simply the loads you use which will dictate the speed and the specific adaptation. But if you are looking to maximize your force output, you're going to need to activate as many motor units as you possibly can in your training sessions. This is exactly why I wrote about PREP SETS. To read that article CLICK HERE.
Your body recruits muscle fibers from smallest to largest.
This is called the size principle: smaller, endurance-oriented type I fibers activate first, then the larger, higher-threshold type II fibers activate as force demand increases. Some people will refer to "high threshold motor units". My interpretation is that is an interchangeable phrase for type II muscle fibers that are harder to get going—they need more demand, more intent, or more effort.
Three practical ways to increase motor unit recruitment
There are three main ways to create the force demand that pulls in those high-threshold motor units: duration (fatiguing sets), speed/inertia (tempo/transitions), and load (heavier weights). Each method has pros and cons, and the best programs use combinations intelligently.
1. Duration: pushing sets toward failure
Longer-set duration (e.g., taking a set to failure or near-failure) increases demand as reps accumulate, and toward the end of the set you recruit more motor units to keep going. That can be useful for hypertrophy because longer time under tension helps the growth signal.
Downside: duration-driven work generates a lot of fatigue, and fatigue itself inhibits motor unit recruitment. If you burn out too fast you lose the ability to produce high force later in the session, which can be counterproductive for strength or multiple heavy sets which I promote for myofibril strength and hypertrophy.
2. Speed and inertia: using transitions and momentum
“There are no warm-up sets. There’s just prep sets.”
When you use speed—especially at transitions from eccentric (lowering) to concentric (lifting)—you tap the inertia of the weight. A lighter load moved with fast transitions creates very short, but very high-force demands that recruit extra motor units without the prolonged fatigue of long sets. Place a 10 lb all on a scale, it reads 10 lbs. Now think of throwing a 10-lb ball onto a scale: the momentary reading spikes way above 10 lbs. Those short spikes expose your nervous system to higher demand in small doses.
Use-case: prep sets that emphasize quick transitions. Submax weights moved aggressively can prime the nervous system for heavier work. Unlike the longer durations sets, these sets can be repeated much more and yield much less fatigue.
Downside: those high-force bursts are short. For hypertrophy, the total time under tension may be too brief; for maximal strength you need heavier loads and longer acceleration phases. So speed work is a tool, not a complete solution.
3. Load: simply lifting heavier weight
Heavier loads require more force and therefore recruit more motor units. That’s the most direct route to turning on high-threshold fibers. But heavy work also produces more central and peripheral fatigue, which limits how much volume you can do.
Downside: heaviness restricts volume—you can’t repeat many heavy sets without performance dropping. The trick is to use heavy loads strategically to prime the nervous system, then exploit that primed state with lighter, faster or volume work in the form of backdown sets.
How to combine these methods—practical templates you can use
I use all three methods in various ways in programming. Here are a few practical templates you can try:
Heavy single then backdown reps for volume: Work up to a conservative single (a heavy but not all-out rep). Then take ~20% off the bar and do multiple sets at that easier weight. The heavy single recruits lots of motor units; when you drop the weight those units don’t instantly turn off, so the lighter sets “fly” and you can accumulate meaningful tonnage for hypertrophy and strength. This is also the idea behind swinging a weighted bat a few times, then swinging the regular bat—it will feel much lighter (and faster).
10x1 explosive sets with a top set: Do 10 sets of 1 rep at ~80–85%, each performed as fast/aggressive as possible (use quick eccentrics and transitions). After these prep singles, take a crack at your top set for the day up to your best set of 1 rep. This method recruits a lot of motor units without the fatigue of heavy multiple-rep sets and can help you hit new daily maxes.
Example from Powerlifting: I work with powerlifters. It's not uncommon for a lifter to warm up to 375, but they are opening with 350. They purposely ramp up above their opener to grab the extra motor units, making the opener fly. It is my belief you are still grabbing motor units with each set that is not accumulating fatigue. You are either recruiting motor units or taking on fatigue, no in between.
How I personally do it
I also use this method on Super Sets... I use all 3 methods: Duration, speed and load in that order. I use duration on single joint exercises and then speed on the primary lift of the day then load on that same primary lift. Here's an example for a Bench Press day:
Duration recruitment: 3-4 rounds in superset fashion
+ Chest Fly- Sets of 12-15
+ Cable Tricep Extensions- Sets of 12-15
With these duration sets, I use a RIR (reps in reserve) of about 5. That means I’m purposely leaving 5 reps in the tank to avoid too much fatigue. Another thing I do is add speed to these sets after the first couple sets.
Speed set recruitment: 3-5 sets
+Bench Press- I’ll do sets of 5-10 reps as fast as I can. I add weight a little at a time, working around 30% up to 60-70% trying to move the bar up AND down as fast as I can. I don’t do any reps that take on fatigue here, I stop before the bar starts to slow. This helps me ramp up without burn out
Load set recruitment: 1-3 sets
+Bench Press- depending on the day but generally I add load either to my working sets or past my working sets if back down sets are on the agenda. A lot of times adding load up to my working sets is enough to get me where I need to be to accumulate high quality high output sets and for my working sets I’m avoiding fatigue. That is why you may have seen me talk about this but majority of my working sets I follow rules. Rule #1 all reps in a row. This shortens set duration, great for avoiding fatigue and it prioritizes speed and effort with is great for motor unit recruitment. Rule #2 no sticking points or grinding reps. Reps that are too slow take on too much fatigue. I save those reps for the last set or 2 and I always end with a “top set”. In the top set you can break all the rules. You don’t have to savor fatigue because you’re done with the exercise and when you change the exercise you often aren’t affected from any fatigue at all. In fact it really sets you up for the secondary strength exercise. This is EXACTLY what we do in Super Sets. Start a FREE 10 day trial CLICK HERE.
Why these tricks work (and why the “primed” feeling matters)
When you briefly force your nervous system into a state of high recruitment, you get a temporary performance boost. I’ve described it as feeling like a superhero for a short time. Use that window to hit a PR, to set faster work, or to do higher-quality volume. This is what my low rep hypertrophy program Super Sets depends on. This is why I include so many words in my programs because the words I include in the training—how and why to lift a rep—matter as much as the numbers. Intent, tempo, and structure change outcomes.
Practical rules of thumb
Understand the goal: hypertrophy needs tension and volume; strength needs heavy load and quality neural recruitment; speed needs high intent and short, explosive bouts.
Use a mix: heavy primes + explosive prep sets + targeted volume often yield the best long-term gains.
Avoid burning out: duration to failure and constant maximal heavy loads both generate fatigue that reduces recruitment capacity—plan recovery and management accordingly.
Experiment with simple templates above and track how weights “feel” after priming methods (heavies, weighted bat swings, or fast prep sets).
Final thoughts
Motor unit recruitment is a foundational idea that should change how you structure sessions. Don’t think of sets and reps as just numbers—think about the demand you’re creating on the nervous system. Use duration, speed, and load strategically and in combination to recruit more fibers without destroying your recovery. Try one of the templates above for a training block and see how lighter weights start to feel far easier after priming.
If something here clicked for you, experiment and tweak your programming. Feel free to reach out to me with questions, test a block of training, and pay attention to how your bar speed and perceived effort change after priming. That’s where the magic happens.
Shop my programs or hire me as your coach. Training is what I live for, I want to share as much as I can and help others rise above the norm
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