The Science of Motor Unit Recruitment Part 3

Motor unit recruitment is a seemingly straightforward process as I covered in part 1 and part 2 of this series. But like anything with the human body, eventually a simple explanation becomes, well, not so simple once you look at physiology on a microscopic level.

Just consider the myriad of tasks your motor units must respond to, from explosive “fight or flight” physical reactions to strenuous isometric contractions to landing on a dime after unleashing a double backflip from the uneven bars.

Does the nervous system always follow the same motor unit recruitment pattern, regardless of the task?

Before I get to that, let’s recap what I’ve covered so far. Muscle contractions are controlled by your nervous system and motor unit recruitment occurs in an orderly fashion as more force is required. In the gym, force increases when you lift a light weight faster, or when you lift a heavier weight. Light weights recruit your smallest/slowest motor units, and then additional larger/faster motor units are recruited as force escalates.

For four decades it was assumed that this orderly recruitment was how human neurophysiology was designed to work under normal conditions. Any research which showed otherwise was usually performed on animals. And as any good scientist knows, what’s shown in the lab with animals often doesn’t carryover to humans. (You only need to look at the research on myostatin and the Arnold-esque bull to know this is true.)

Indeed, when I finished my graduate work in neurophysiology in 2005, an orderly recruitment of motor units was still considered the best explanation of how the nervous system responds to demands for higher force.

But science, like any other reputable discipline, eventually evolved to the point where more precise testing methods could paint a clearer picture of what’s really going on. In 2006, Wakeling et al (J. R. Soc. Interface, 3, 533-544) released a study that analyzed muscle fiber recruitment in the three plantarflexor calf muscles: soleus, medial gastrocnemius, and lateral gastrocnemius.

What they found was surprising. By using EMG analysis they demonstrated that the medial gastroc muscle could preferentially recruit the fastest (largest) motor units, even when the slower motor units could still fire.

This research is intriguing because it flies in the face of the orderly recruitment postulate. According to the size principle, if the largest motor units are recruited, the smallest motor units must be working at full force to keep up. However, Wakeling’s team demonstrated a drop in activity from the smaller medial gastroc motor units while the largest ones were working at breakneck speed.

How was this possible? According to the study, an interneuron in your spinal cord, the Renshaw cell, can inhibit the small/slow motor units. Look at the image on the right and you’ll see two motor neurons (in black) that exit your spinal cord and control your muscles. You’ll also see an arrow from each motor neuron that feeds information back to the Renshaw cell (shown in red). This Renshaw cell takes information from the motor neuron and can inhibit the small motor units in order to favor the large motor units.

Think of the Renshaw cell as being a general in the military: it distributes fire power to the units that need it most.

Too much science? Ok, let’s step back and look at the big picture.

When your goal is to get bigger, stronger, or faster, you must recruit the largest motor units. This is accomplished by lifting heavy some of the time, and lifting fast other times when you’re training with lighter loads. How did Wakeling’s team target the largest motor units? With fast contractions. Here’s a line from the paper:

“…one factor that can lead to the preferential recruitment of faster motor units is rapid shortening velocity of the muscle…”

Everyone knows that getting bigger and stronger requires you to lift heavy. But some people still aren’t sold on the importance of fast contractions with submaximal loads. Even though this research demonstrates that the size principle might not hold true in every muscle contraction, it still gives credence to the point I always try to make in my books and seminars: you must tap into the largest motor units to get rapid results.

The Wakeling study is just another piece of science which helps explain the power of explosive contractions to get you there.

Stay focused,

The Science of Motor Unit Recruitment Part 2

In my first installment of this series, I explained how the incredibly important size principle works. It’s crucial to understand that information, so if you haven’t checked it out you can do so by clicking here.

To recap, all movements start in your brain, and then travel down your spinal cord where the signal stimulates the motor neuron to contract your muscles.

Now, I’m going to take things a step further by explaining the essential component of any training program that’s designed to build muscle, boost strength, or burn body fat.

What is the essential principle that I live by? You must recruit as many motor units as possible with every rep of every exercise. The only way to do this is by following training parameters that tap into your largest motor units.

Here’s why that’s important. You see, according to Henneman’s size principle, if you’re tapping into the largest motor units you’re also recruiting all of the other motor units (from smallest on up).

Check out the graph on the right that shows the relationship between force and motor unit recruitment. The highest levels of force coincide with the highest level of motor unit recruitment. There’s no reason to ever do a rep, set, or workout that doesn’t target as many motor units (muscle fibers) as possible, therefore, keep this graph in the back of your mind.

Ok, at this point a logical question surely popped into your mind: “How do I recruit all my motor units?”

There are two ways: lift as heavy as possible, and lift as fast as possible. Now, keep in mind that heavy weights won’t move quickly, no matter how hard you try. But they don’t need to. When the weight is heavy enough to only allow three or four reps, you’re recruiting all your motor units because it takes every ounce of effort to get the weight moving.

Where many people screw up, however, is with submaximal weights. I’m talking about lighter weights that you could move faster, but don’t. If you start with a weight you could lift 12 times, and if you lift with a slow tempo, you’re probably recruiting about 60% of your motor units. But if you accelerate the lift from the first rep as fast as possible – wham-o! – you’ve tapped into all the motor units that were sitting on the bench.

So there are two ways to recruit all your motor units: lift heavy weights some of the time, and lift lighter weights as fast as possible other times.

There’s another essential aspect that I want to mention with regard to lighter weights. It’s not the load of the weight that’s important – it’s the effort and intensity that will make or break your results. With enough focus and drive you could theoretically recruit more motor units with 50% of your one-repetition maximum compared to, say, 75% of your one-repetition maximum.

Now, here’s a critical component of the equation that many people don’t think about: “How long can I sustain maximum motor unit recruitment?” This, my friends, is the key to getting this powerful training concept right.

Remember I said that the goal of any rep, set, or workout should be to tap into your largest motor units (aka, largest muscle fibers)? Well, your biggest, strongest muscle fibers can’t maintain their activity for long since they rely on the short-acting ATP-PC energy system. This is a readily available supply of energy in your muscles that allows you to immediately tap into the “fight or flight” response. However, since it’s a small pool of energy, it can only maintain your maximum efforts for 10 seconds.

In other words, you only have 10 seconds of available time to recruit all your motor units. This is why so many lifters immediately got results when I told them to switch from 3 sets of 10 reps to 10 sets of 3 reps. With 3 reps, you’re finishing each set in less than 10 seconds. In either case you’re performing 30 total reps, but with 3 reps instead of 10 reps per set, you’re able to take advantage of maximum motor unit recruitment with every set.

Now, keep in mind that the “10 seconds maximum” I mentioned can differ from person to person. Some lifters will only be able to sustain maximum motor unit recruitment for 6 seconds, whereas others can pull it off for 12 seconds. That’s why it’s important to know which cues tell you that motor units are dropping out of the task. It’s important to keep in mind that the largest motor units are recruited last, but drop out first. So you must first tap into them as quickly as possible by lifting heavy or lifting lighter weights fast. Then, you must know when those largest motor units are dropping out.

How do you know? There are three cues. First, your speed will slow down dramatically. Second, your range of motion will shorten. Third, your technique will break down. These don’t all happen in the order I mentioned. For some exercises, such as the pull-up, your range of motion will typically shorten before your speed slows down. For technical lifts such as a hang snatch, your technique will falter before your speed decreases. However, for most common strength exercises your speed will dramatically slow down when motor units start dropping out.

“The last few reps of a set is where the results happen,” has long been the dogma in resistance training circles. The theoretical reason why some coaches said this was true is because they figured that additional motor units were recruited at the end of a long, agonizing set to failure. However, if you look at the neuroscience research it’s clear that this postulate holds no water.

If you recruited more motor units in the last few reps to failure, the set would get easier and the speed would increase. Since this doesn’t happen it’s time to look at a more progressive way of training. Lift heavy, lift fast, keep the sets shorts, and avoid failure. Those are the keys to maximum motor unit recruitment.

In my next installment I’ll discuss some exciting new research that uncovers new ways to tap into your largest motor units.

Stay focused,

The Science of Motor Unit Recruitment Part 1

Understanding the science of motor units is absolutely essential for getting results, whether you want to gain muscle, build strength, or torch body fat. Building muscle fast requires you to recruit, and fatigue, all your motor units so they’ll grow. To reach elite levels of strength you must train your body to tap into the biggest, strongest motor units as fast as possible. And to burn fat, it’s essential to boost the metabolic cost of the exercises in your workouts as high as possible. How do you skyrocket the metabolic cost? You guessed it, by recruiting more motor units.

Take a close look at the picture above. The yellow area is your brain, spinal cord, and a bunch of nerves that travel throughout your body. It’s the output from this electrical mainframe that controls your muscles.

That’s why, over the next week, I’m going to cover everything you need to know about the science of motor unit recruitment, along with some intriguing new research that could change the way we think about motor units. So let’s start at the beginning.

“What the heck is a motor unit, anyway?” That’s probably a question you’ve asked yourself once or twice. As defined by my grad school bible, Principles of Neural Science: “The axon and the muscle fibers it innervates constitute a motor unit.”

Clear as mud, eh? In layman’s terms, the motor unit is a collection of muscle fibers along with the nerve that tells those muscle fibers to contract. Each group of muscles is innervated by only one nerve. A nerve can can talk to 100 muscle fibers (small, eye muscles), or thousands of muscle fibers (large, hamstrings muscles) or somewhere in between.

Before you curl a dumbbell an electrical signal starts in your brain and travels down your spinal cord to the lower cervical region where it activates a different nerve that goes out to your biceps. This nerve that exits your spinal cord and reaches your biceps is a motor neuron. (“Neuron,” by the way, is just another name for “nerve.”) The activated motor neuron releases the neurotransmitter, acetylcholine, which attaches to receptors on your muscles that create a cascade of events that contracts your biceps. (Of course, this all happens in fractions of a second.) Continue reading

Get a Stronger, Harder Core: Hand Walkout

Of all the core training exercises out there, one of my favorites is the hand walkout. It builds strength in your anterior core and lats very quickly, it trains the abs isometrically like Dr. Stuart McGill advocates, and it’s an excellent alternative to the ab-wheel rollout. Plus, the hand walkout will boost your squat and deadlift by augmenting the transfer of force between your legs and upper body. And since it requires no equipment, you can do it anywhere.

But it’s also an advanced exercise that I only use with clients who are ready for it. Here’s a brief video of my client, MMA superstar Ralek Gracie, performing the hand walkout.

Importantly, Ralek is an advanced athlete and that’s why he needs advanced core training exercises and ab exercises for men. This exercise might be too difficult for you right now, and there’s no reason to jump straight into a high-level exercise unless you’re ready.

How do you know if you’re ready for the hand walkout? You must first be able to perform the modified hand walkout (knees down) for 10 perfect reps.

Here’s how to do the modified hand walkout:

1. Start on all fours with knees and hands shoulder width apart. Hands are directly below shoulders (left pic).

2. Tense the glutes, brace the abs like someone is going to punch you in the stomach, and then “walk” your hands forward. The hips should shift forward as soon as you reach your left arm out (center pic).

3. Continue walking your hands out until your abs are just a few inches off the ground (right pic). Reverse the movement by walking your hands back to the starting position. That’s one rep.

Once you can perform the modified hand walkout for 10 reps, it’s time to take a crack at the hand walkout. You’ll probably be surprised how much more difficult it is so don’t try to do too much too soon. Before you attempt your first set of the hand walkout, perform 5 reps of the modified version to prepare your joints and muscles. Next, do three sets of the hand walkout for as many reps as possible. Continue reading

How to Fix Your Bench Press

The bench press is the most popular strength-training exercise in the U.S., but most people don’t know how to do it correctly. I’ll give you full disclosure and admit that I’m not a huge fan of the exercise.

The reason is not because the bench press is “bad” per se. It can add strength and size to your upper body pushing muscles and this, in turn, will carryover to many sports.

The problem I have with the bench press is this: out of all the strength-building exercises it’s one of the most common exercises that guys screw up. When you bench press with poor form it can really wreak havoc on your shoulders and elbows. That’s why it’s imperative to get the technique right.

Luckily, Jim “Smitty” Smith has put together a comprehensive list to ensure that you’re pressing with perfect form. With this information you’ll build awesome upper body power while saving your joints. Continue reading

Fix Your Deadlift

A big deadlift is essential for building full-body mass and strength. So today I’m passing on some awesome tips from strongman and body transformation expert, Jim “Smitty” Smith.

Smitty knows how to build some serious muscle and strength. He’s spent an incredible amount of time in the trenches and he’s an expert advisor for Elite Fitness Systems and Men’s Health.

So let’s get this started!

CW: Ok Smitty, before someone puts effort into boosting his deadlift he must first figure out if there’s a problem. How do you access the correct deadlift technique from the start?

Smitty: There are three primary elements to consider when correcting deadlift flaws. First, is the person missing the lockout? Second, are the knees buckling in with sumo deadlifts? Third, is his missing off the floor?

CW: I agree that those are three common problems. How do you fix them?

Smitty: First off, you have to deadlift with good form. If your form is off, it will lead to you missing the lift, typically right off the floor. There are seven things to consider right way.

1. Shins on the bar – you must make sure you’re as close to the bar as possible. This shortens the distance between the center of gravity (COG) of the bar and the COG of the lifter. This is the most advantageous leverage position.

2. Big air – you have to catch a big air in your stomach to increase intra-abdominal pressure. This is an essential step for immediately boosting your strength.

3. Push your abs out – when you push your abs out (after sucking in a lot of air) it will provide you with a natural belt to ensure your lower back and abdominals are braced strong. This technique is further enhanced when you actually wear a belt because you’ll be able to force your abdominals out against the rigid belt.

4. Don’t jerk the weight off the floor – instead, push the floor away after you develop a high level of full-body tension.

5. Push your knees out – as you stand up, push your knees out to the sides to keep them from buckling in.

6. Keep the bar against your body throughout the lift – this, again, maximizes your leverage so you can lift more weight.

7. Lockout with a powerful glute contraction – don’t hyperextend your lower back. Lockout your hips by forcibly contracting your glutes.

CW: Good stuff, let’s move on. Some technique problems are due to a guy (or gal) just being plain weak. Which factors do you consider most important for building strength that carries over to the deadlift?

Smitty: To develop full-body, deadlift strength you must focus not only on your posterior chain, but also your core strength, upper back musculature, and grip. This time, there are four factors that need special attention.

1. Strengthen the posterior chain – Romanian deadlifts, stiff-legged deadlifts, glute-ham raises, reverse hypers, partial range lockouts (rack lockouts), and deadlifting while standing on plates will all lead to huge improvements.

2. Strengthen the core – compound movements, L-sit pull-ups, medicine ball exercises, and the ab wheel are all effective ways to develop the core.

3. Strengthen the upper back – face pulls, pull-ups, seated rows, and bent-over rows work best.

4. Strengthen the grip – the thick bar hold, rack hold, and plate pinch all work great. Also, use an unmixed grip (both palms facing down) for as long as you can while working up your deadlift poundages.

CW: I give that checklist my “thumbs up.” Anything else that’s vitally important?

Smitty: You bet. The last thing I want to tell your readers is this: to pull heavy you must be mentally prepared. When you approach the bar you have to be ready to pull the trigger!

Right now Smitty is offering a discount on his outstanding system, AMD 2.0. If gaining size and strength is your goal, I highly recommend that you check it out by clicking HERE.

Stay focused,