Motor Unit Recruitment in Resistance Exercises

Hi everyone,

Charlie often mentions in his materials that certain exercises will have a higher MU recruitment than others (e.g. circa 65% for the Back Squat vs. 35% for the Bench).

This notion makes a great deal of sense to me from a logical standpoint (i.e. more muscle mass worked/involved should in theory = more MU recruitment/contribution), but I wanted to see if there was any published research supporting this.

I have not had much luck so wanted to ask if anyone knows of/can direct me to any research that specifically measures or comments on MU recruitment for different key resistance exercises in this context, or where Charlie received his information on this area from?

The other thing I would like to add (and hear people’s thoughts on) is that in my opinion MU recruitment is not necessarily the only item in the picture, as things like % of Maximal Voluntary Contraction will also influence the “effect” of a given exercise and/or summated output from a given amount of MU recruitment (and therefore total stress on the system + CNS).

Thanks in advance for your time and look forward to hearing people’s thoughts,


Recrutment patterns vary greatly from person to person add the experience factor, brachiomorphs vs dolicomorphs etc.

What I think Charlie was pointing Is the “estimation” of work for the overall muscle mass and how much It would cost the CNS to fire all that. When we know that, It makes us more concious about the whole volume/intensity gestion.

For example: If the quadriceps is recruited at around 65% in a given exercice for two athlete. That may represent 20% of muscle activation total vs Full body muscle and only 15% in the other???

If you look at %MU activation there are many research, Bompa provide a simple presentation in his book: “Periodization training for sports”. T-mag have had some good article on this too.

one of the series

here is also very good information link:

A sprint activates 234% more mean gluteus maximus muscle than a vertical jump.

In order, the hip extension exercises with the highest glute activation are
the kneeling squat (67%)
deadlift (55%), sumo deadlift (52%)
Zercher squat (45%).

In order, the hip hyperextension exercises with the highest glute activation are the
single leg bent leg reverse hyper (122%)
hip thrust (119%)
pendulum quadruped hip extension (112%)
bent leg reverse hyper (111%).

Since popularizing the hip thrust exercise, I’ve heard a lot of experts “chime in.” Some say that they prefer pull-throughs since it’s a similar motion. Listen, the hip thrust is to the pull through as the bench press is to the standing cable chest press; good to do every once in a while, but a stable base and a barbell maximizes activation.

moderators let me know If anything Is done incorrectly “copyright”

Hi Adonail,

Thanks very much for the reply, I agree that recruitment patterns will differ between many individuals which is why I mentioned the importance of MVC in addition to MU recruitment.

I also appreciate the Bompa suggestion, will take a look in there but from memory he didn’t seem to have much in the way of explanation where he got those figures from?

Similarly, the T-Nation articles are interesting however in my opinion they don’t exactly constitute real studies (for one there is no mention of methodological procedures) so I am wary of taking the information from there as conclusive. In this format I would say these articles mainly represent well-researched opinion rather than anything else.

I know Bret well and asked him my original question this morning, and he said he didn’t have an answer either but would be very interested to know the same thing.

In a nutshell, I’m just curious to see where the specific numbers/estimates Charlie mentions originated from, and if there has been any more sound research done on this topic since he formulated them.



What Is your background? You seem to be very critic, that Is a good thing. But, If your purpose Is sprint performance, I am not sure you will find the holy grail If the real information exist at all.

My athletic background is professional Rugby, which is also the field I currently work in.

You are very right, the information might not exist but I would never know if I didn’t ask :slight_smile: as I stated above I am just curious to know what this info (which makes sense to me) is based on.

manual therapist from what field?

Stay here, we need more people like you to keep this site alive and informative as well.

My take on the % are simply based on muscle recruited and size % of the total body muscle mass estimation.

Thanks Adonail, my initial therapy education was in myofascial + trigger point therapy.

Charlie’s Motor Unit diagram was intended to be a conceptual diagram that shows relative motor unit involvement for various activities/exercises. It was not based on any particular research or empirical evidence. If anything, it was based on Charlie’s own experiences as an athlete and coach, and his intuitive knowledge. In many cases, I truly believe it was based on his own observations with regard to both fatigue and adaptation in athletes he coached.

But there were no scientific studies done or rabbits sacrificed with muscle biopsies or needle EMG’s for this diagram. In fact, I believe we were sitting in his dining room, passing different ideas back and forth on relative intensities of various activities. We started with sprinting on the left side of the diagram and a bicep curl on the right side of the diagram, and the rest was history. The diagram is meant to create more thought on the subject of exercise selection, nervous system involvement and resultant fatigue. It is not meant to be an absolute priority list of exercises for a training program.

As someone mentioned earlier, everything will be individual specific. If an athlete does not have the coordination or aptitude to perform a clean and jerk, snatch or other variation, there’s no point in selecting that exercise as a high intensity stimulus. They may be better served by combining other exercises (i.e. heavy squat and heavy bench + sprint - as was done with BJ). The exercises listed in the MU diagram have the potential to involve a high proportion of Motor Units, but many people do not have the ability to take advantage of that potential. So, they are forced to keep things simple… which isn’t all that bad an approach.

All makes sense and completely agree, thanks for outlining that NumberTwo.

Number Two, a quick follow up question

Say you had two exercise choices in a similar area in regards to both MU activation and muscles worked (eg. squat vs. deadlift) and a relatively large discrepancy in ability to load between the two (deadlift well above squat). Would it be more effective to focus your efforts on the one that you were best at and not really worry too much about “balancing” it out. In effect what I’m asking is do you see any potential problems with using deadlift and bench as the primary strength movements and not really performing squats as a weight exercise (but maintaining the movement in warmup activities)? My thinking on this would be that it is relatively similar to Ben not really using the clean and sticking to squat/bench. Your thoughts?

Coxy24 - It’s possible to make that sort of exchange. It may depend on several factors. Some athletes just do not have good squatting abilities - particularly those with long legs (particularly long femurs) that create postural problems in a squatting movement. Many of these athletes are able to deadlift more effectively (possibly because they also have long arms).

My only concern with the deadlift is that many athletes over-load and lose postural integrity in order to achieve higher loads (i.e. some can lift more with very poor and dangerous technique). Also, deadlifts also tend to create a greater duration of time under tension (perhaps because it is concentric-eccentric, as opposed to eccentric-concentric) which can lead to greater peripheral fatigue that can interfere with other qualities.

It also depends on the sport you are training for (i.e. sprinting vs. american football) and the time of year. For a sprinter, you may opt for deadlifts earlier in the program, but transition to something with less muscle tension (i.e. jumps, throws). Whereas for the footballer, you may keep the deadlifts in the program for the entire off-season training program.

As a coach, you have to make that judgement call based on the information you have available. That’s the great thing about Charlie’s MU graph. It gives you some options with which to make an informed decision on exercise selection. And, ultimately, you are assessing the efficacy of your training program, not by how much you can lift during the program, but how much you have improved in your sport/event of choice.

Thank you for the response. I guess I was just looking for some reinforcement on something I’ve been drifting towards in my own training. Perhaps because of my build (similar to the one you described), I seem to get more out of deadlifts than squats with out really experiencing recovery issues (provided I’m not trying to max right out). Just wanted to see if anyone could give me a convincing reason to go against my instincts in regards to choice of exercise.

BTW, I’m a hockey player (or as much as I’m anything anymore)

Sounds good. With hockey players, there tends to be issues with tight hip flexors which may make squatting more difficult. Also can lead to problems in the groin. I’ve run across this before with hockey players.

You are probably on the right track with your instincts.

I figured I’d chime in here as I’ve been utilizing the deadlift for about 2.5 years now. I hit a lot of squats when I first started lifting seriously around the age of 21 (I’m 28 now). After a couple of major hamstring pulls over those first few years, I basically was terrified of lifting weights. Regardless of how long I had been squatting, I just never could get my legs to feel right. Perhaps there was something wrong with my overall approach to training then; nonetheless, I really backed away from the weights for a year or two. But then the deadlift made its way into my life.

Rather than trying to write the perfect paragraph, I’ll just list a bunch of things I’ve experienced since using this lift:
-I can be very aggressive in the weight room without needing a spotter (I train alone for the most part).
-If I have an off day/set/rep, the weight just stays on the floor. There’s never the risk of being crushed.
-My legs feel excellent after a session. I don’t have a scientific explanation for this, but my flexibility is at its peak right after lifting.
-My overall body has developed more from adding this one lift than any other (e.g., shoulders, back, core).
-Its efficiency shouldn’t be overlooked (see last bullet). You can hit so many things with this one exercise.

I might have one of those body types that just gravitates towards this lift as mentioned earlier. I’m 6’, 167lb, and more legs than torso. My current 3 rep max is 395.

I’ve found the time under tension to be much less for deadlifting than it was for squatting. Once the bar is across your back for the squat, you have to step out of the rack, go down, come back up (for however many reps), and then bring the weight back to the rack. When deadlifting, I just pull the weight from the ground and essentially use a controlled drop to get it back down. This has minimized - perhaps even eliminated - micro tears in the hamstrings, which I believe is a big factor in my lovely hamstring experience these days. I follow a CF 3-1 structure with my speed work, so I’ve aligned lifting to fit well with that. I lift after speed sessions, where I only utilize two lifts: deadlift and bench. My progression each cycle is as follows:

Week 1: 2 sets of 5 reps
Week 2: 3 sets of 4 reps
Week 3: 3 sets of 3 reps
Week 4: 2 sets of 5 (unload with lower weight)

So my intensity is increasing through the 3 weeks, I unload the 4th week and then come back with the same 5-4-3 progression, but at a higher level. My bench workouts follow the same approach. So after a speed workout, I only do around 20 lifts - although they are all pretty intense. This has worked well for me, and I sure don’t feel like many, if any, muscles are being neglected. I should note that I still do some general conditioning on low intensity days, where I may hit some additional core work, pullups, pushups, or medball throws.

I suppose, the eccentric part of the deadlift can be avoided, if/when needed, by just dropping the bar, something that is much more difficult and impractical to be achieved with the squat, for example, with pins etc. Charlie’s chart is very helpful, indeed!

When I think of improving or maximizing motor unit recruitment, I don’t think of overall, total body recruitment. Obviously exercises that involve larger and/or multiple muscle groups will have a higher total recruitment of muscle fibers, but I don’t see the benefit.

When I think of improving or maximizing MU recruitment, I think in terms of improving recruitment within discrete muscle bundles, improving rate coding, and improving coordination/synchronization. This is done by performing maximal effort reps, either high intensity all out reps, or by pushing the muscle to failure. Zatsiorsky provides a nice summary in thisarticle. As CedricU points out, these type of articles/opinions are not necessarily science, but are generally accepted to by opinions of highly respected scientists based on their extensive research and observation.

The simple answer is that there is no proper answer - especially in the application of the theory. MR has a complex series of variables, which are all interdependent.
Charlie’s chart was more for illustrative purposes (conceptual is a better word) from an ideal perspective as opposed to a concrete guide. Also MR will vary as time progresses and the athlete develops over time, so even if you can establish the MR%'s for an athlete at a point in time - the progressions and developments will lead to different %'s as they develop further.
This is why I am very skeptical of people who claim in X movement Y muscle has Q% recruitment. Oh yeh …? Is that so? For what demographic - you alone? How many cases? What training?
So in summary, from a practical point of view, I’d would look at other mechanisms for the ‘application’ of this concept. Where it is most important is from a CNS fatigue consideration.
Regarding the suggestion, not to think of total body recruitment, I would disagree. It does depend on the context, but from a Performance point of view, especially in team sport - whole body recruitment is all that matters!
Also, regarding Hockey - or other team sports, MR is only one factor in selecting exercises - it is not always the main one either.
One important final consideration is also that the aim of training should not be to maximise MR in a specific lift or lifts, but in the exercise or sport you are competing in.

I agree that understanding CNS response is important in terms of recovery issues, and is also important as an overall CNS stimulation, which is what I remember Charlie discussing most often.

However, I often see statements discussing attempts to improve specific motor unit function in a specific lift or event. Improving recruitment and coordination in those specific muscles, producing a specific adaption, is not enhanced by stimulating unrelated motor units by altering the exercise, even if the overall CNS stimulaton is higher. In fact, I would go as far to say that this would be disruptive to the specific goal.

Sometimes there is confusion on this issue and I only wished to offer a clarification.

This thread has me re-thinking my powerlifting training program/schedule. I have always cared the most about squat, so I squat hard and heavy on Monday…when I am the freshest. I train legs twice a week, but I can’t go heavy twice. So I squat heavy Monday, and do speed deadlifts on Thursday…8x3 w/ roughly 50%. In the past I have noticed significant and drastic benefits following squat workouts where I focused on speed with lighter than usual weights. Watching Pat Mendes squat 800 ATG with no belt, spotter, or safety catches made me believe that squatting fast is the best way. If squatting fast is so effective, and deadlifts train the highest level of MU recruitment, it would only make sense for me to reverse my schedule, training deadlifts hard and heavy on Monday…a sort of Max Effort Day, and a speed/dynamic squat day on thursday. Thoughts?