The Myth of Non-Functional Hypertrophy

If you read my articles you know that explosiveness is largely dependent upon strength, and strength is fairly influenced by muscular growth, or hypertrophy. In this article I'd like to address another topic along these lines and this the topic of functional vs non-functional hypertrophy. Non-functional hypertrophy refers to gains in muscle size that aren't associated with an improved capacity to produce force. "Functional" hypertrophy refers to gains in muscular size that improve maximal force production, and thus carry over into the real world. Simple enough.

Manufactured Strength Vs Natural Strength

Before I get into it I'd like to point out that no supplemental training method is perfect and has a perfect transfer to sport. The practice of adding strength and size thru weight training in an attempt to apply the benefits of that strength and size to a sport is effective but it won't ever be perfect. You're basically manufacturing something that wasn't there to begin with - You're allowing your body to adapt to one stimulus and then applying those adaptations to another area. It really is cheating in a way. The only thing that isn't cheating would be actually playing the sport and letting your body adapt naturally. However, we know there are limits to that. But this is one reason why people that have "natural" strength, size, and power will generally have a "functional" strength advantage over those who have to manufacture it. Reggie White, Lawrence Taylor, and Mike Tyson rarely if ever lifted a weight. Compare them to muscled up guys like Frank Bruno, Tony Mandarich, and Vernon Gholston. Manufacturing size and strength isn't perfect regardless of how you acquire it, but it beats the alternative and can allow you to compete at a level you wouldn't have.

Myofibrillar growth vs Sarcoplasmic growth

Now that i've got that out of the way, let's talk a little bit of muscle physiology. In a muscle cell you have the actual protein content in the cell, or the myofibrils, and you also have fluid surrounding the protein, the sarcoplasm. Strength is primarily influenced by the amount of protein contained in the cellular filaments, or the myofibrils.

There is a belief in the training world that certain types of training can influence the growth of one of these components over the other. The belief is that heavy low rep weight training favors growth of the myofibrils and builds muscles that are as strong and "functional" as they look, if not stronger. In contrast, higher volume/higher rep training (bodybuilding methods), are often believed to favor growth of the sarcoplasm. Since the sarcoplasm consists of non-contractual fluid it is supposedly possible to gain large amounts of size without any increase in strength. This is deemed to be responsible for the so called non functional strength or "bodybuilding fluff" lended to bodybuilding methods. Muscles that aren't as strong as they look or muscles that are slow and unathletic.

For this reason athletes are often encouraged to train heavy and use lower repetitions in their training. There is a belief that training with higher reps and shorter rest intervals and lighter weights builds only non-functional strength.

What Really Happens

However, when we examine this claim critically, science demonstrates the size of the sarcoplasm is limited by the size of the myofibrils. In other words, a cell can only hold so much sarcoplasm and that amount is limited by the size of the myofibril within it. Additionally, more than a handful of studies have tried to differentiate myofibrillar from sarcoplasmic hypertrophy with different prodocols and loading parameters. In every single one of them myofibrillar growth always comes out well ahead, typically by a 2-3 x margin.(1-5) Thus, it would seem it is impossible to increase sarcoplasmic growth in the absence of myofibrillar growth regardless of what strategies are employed.

This would tend to indicate that sarcoplasmic hypertrophy is mostly a myth. Well, technically it does, but in practical terms non-functional growth does exist, but in my humble opinion it doesn't occur in ways most people think. In the real world non-functional hypertrophy is simply extra glycogen storage. A muscle that has it's energy stores taxed (thru higher volume training) will adapt to store more glycogen, or carbohydrate energy, and this can add a significant amount of extra weight and size.

Fluff and Glycogen

A normal 170 lb male can store about 350-500 grams of total glycogen in his muscles. A 170 lb male whose muscles are trained at fairly high volume can store about double that, or ~1000 grams. Each gram of glycogen attracts 3 grams of water with it, so 500 grams of extra muscle glycogen above average will add an extra 2000 grams of total weight above normal, or about 4.5 lbs. This 4.5 pounds of extra glycogen and fluid will be stored in the muscles and will "appear" to be solid muscle weight, but it's really nothing more than energy and water. Four and a half pounds may not sound like a lot but take a look at a 4.5 lb steak next time you're in supermarket and you can see that's a considerable amount.

Let's say you take take 2 people with 15 inch arms who train with fairly low volume, so their energy stores are never really taxed. Let's say they do something like 5 sets of 3-5 reps for biceps and triceps twice per week. You keep one of them on low volume and put the other one on high volume, something like 8 sets of 10-12 reps twice per week. The guy on the higher volume protocol might see his arms immediately go up an extra 1/2 to 3/4 of an inch over the other guy, because the extra volume taxes the energy stores in his arms to a greater degree and the body adapts to that by increasing the amount of energy that can be stored in his arms. So their arms will be the same size from a myofibrillar perspective and likely be the same strengthwise but the 2nd guy will have more glycogen storage, which makes his muscles look bigger (and may makes him appear weak for his size compared to the other guy).

A person with a 20 inch solid arm who trains with low volume might be able to add a full inch by increasing his volume.

That's not to say that someone training with higher reps can't build plenty of functional strength and size in the process. As long as he trains with progressive resistance his myofibrils will increase in size just as well as the guy on lower reps, he's just more likely to have a nearly immediate extra gain from the increased glycogen storage in addition to that.

With higher volume training the average bro might be able to gain 5-10 lbs or so of sarcoplasmic hypertrophy across his entire body over what he would on lower volume protcols. Cell volumizers like creatine also attract water into the muscle and add to that. Add in steroids (which often increase creatine storage and water retention) and other cell volumizers and it's fairly easy to see how bodybuilders training at high volumes can add a significant amount of "fluff" weight.

So Why Are Some People Weak For Their Size?

Besides that there is one primary reason why "high-rep" guys might appear weak for their size:

A: They rarely practice lifting maximal weights so they're not as good at lifting maximal weights. Maximum strength is a skill that must be practiced, just like sporting movements are skills that must be practiced. You also see this in reverse. If you take a bodybuilder who regularly does sets of 15-20 reps and a powerlifter who regularlly does sets of 1-3 the bodybuilder will have a hard time matching the powerlifteron low reps sets but the powerlifter will likely have a hard time matching the bodybuilder on high rep sets.

It's also worth noting that weight training is only one way of taxing muscular energy stores and stimulating increased glycogen storage. Anyone engaged in more than a few hours of exercise per week, especially a sport incorporating some form of running, is likely already stimulating these adaptations.

Low Reps and Thickness

What about the claim that low rep power training builds dense, thick muscles? Take a look at the neck and trap development of some of the top powerlifters and strongmen. They have a bulldog like thickness to them that you don't see equaled by many other athletes. Many would have you believe this is solely on account of their style of training, but if you pay much attention to the sport you'll also find plenty of people who train the same way and don't have this look. My explanation for this is that naturally strong people tend to gravitate towards strength sports and naturally strong people are typically incredibly gifted for size as well. They have a ton of dormant muscle cells just waiting to explode, much like bulldogs, pit bulls, and boxers are thicker than other dogs. In general people that grow extremely well off of low rep/low volume training are very gifted for size and would have well above average thickness even without any training.

Rep Range and Fiber Type

Another thought is that repetition range influences the type of muscle fiber (fast twitch/slow twitch) that is built. There is some thought that high rep training (anything greater than 8-10 reps) builds slow twitch muscle fiber and should be avoided. However, slow twitch fibers really don't grow much no matter what you do, and the small amount they can/do grow is best stimulated by the same heavy sets that cause "normal" growth, standard sets of 6-12 reps. If that weren't the case then endurance athletes would all be huge. Regardless of how you gain it, any size you gain will be fast twitch related growth. However, there is something to be said that training can influence the quality of fast twitch fiber that you build.

All muscle fibers exist in a color continuuum with some fibers being pure white and other fibers having a shade of red. Think of eating chicken. The dark meat is tender and red while the breast meat is white and tough. Your muscles are the same way. Some are redder or whiter than others. The slowest twitching fibers are dark red while the fastest twitching fibers are pure white. In between those 2 extremes there will be various shades of white and red. What causes the different color is the amount of capillaries running thru the muscle. The redder the muscle the more capillaries (and oxygen) run thru it. The whiter the fiber the less capillaries (and oxygen) run thru it. Fibers can't completely change types. You can't take a dark red (slow twitch) fiber and change it to a pure white (fast twitch) fiber and vice versa. However, you can change the shade of a given fiber type (slow twitch or fast twitch) to either a whiter or redder variant of the same fiber type.


There are different sub types of fast twitch fibers with some more enduring or more powerful than others. In humans the whiter type II fiber is known as the IIX subtype, the intermediate light red shade is known as IIA. Both of the type II subtypes have equal strength, but the white fibers are more explosive and have no endurance while the redder shades are a bit less explosive with more endurance.

Fiber type------------------------------------Fiber type



<---Greater explosiveness------------------Less explosiveness-->

<---Less Endurance---------------------------More Endurance-->

The IIX fibers can change into IIA and vice versa, but it's arguable how much this is dependent on rep range. For all practical purposes anything you do that causes muscle breakdown/growth will cause an intermediate shift towards more IIA fibers. Actually activity of any kind tends to promote the IIX to IIA shift, even sprint training. Unfortunately, (and this is one reason why I started off this article by saying that weight training isn't perfect as far as transference) if you train with enough volume to cause muscle growth you train with enough volume to cause the shift. Untrained people actually have more IIX fibers than anyone because they don't do anything, - their fibers have no need for any endurance.

Explosive athletes like sprinters and olympic weightlifters have more IIX fiber than others, but it's likely this is a genetic trait. They start out with more, thus end up with more, as science demonstrates fast twitch IIX fibers convert to IIA with any sorta practical stimulus.

So, if you want to avoid fast to slow fiber conversions you have to avoid muscle breakdown, which means you don't grow at all. Is there any way to create a IIA to IIX conversion? Well, detraining is one way to do it. If you want to influence IIA to IIX conversions you need to keep the volume low and avoid muscle trauma. Strategically timed tapers and incorporation of pure explosive training methods can cause temporary shifts back towards the IIX subtype, which is what athletic peaking and proper periodization is all about. For more info. on that read my Fast twitch Machine Articles.

The Real Value of Rep Range

The point is, functional hypertrophy isn't as dependent on rep range as a lot of people think. For all practical purposes what determines whether you're functional or not is what you do outside the weight room - your movement and skill work. Train with 10 + reps, practice your sport, and stay mobile and you'll likely be as functional as they come. Train with 1-5 reps and do nothing else and you can easily be as non-functional as a muscled up hippo.

Take 2 twin brothers that both play football. Both do skill and movement work year around. Over a span of 3 years one works up to 600 x 3 squat never doing anything more than triples. The other does 500 x 10 never doing less than 8 reps. It would likely be about impossible to tell them apart performance wise.

Another example is strongman training which has really risen in popularity in athletic training circles. Take a look at some of the characteristics of the exercises involved in strongman: Flipping a tire all the way across the parking lot, cleaning and pressing a keg then walking around with it, and farmers carries. A lot of strongman type stuff is a lot closer to the "high rep" side of things as far as time under tension goes. But how many people come out and say strongman training sucks as a strength stimulus for sports?

As long as you use progressive resistance you can build solid (and functional) size doing sets of 1 rep or you can build solid (and functional) size using sets of 20 reps. The lower body, particularly the quads, tend to respond particularly well to higher reps, and the upper rep range is a bit higher for lower body than upper body. Twenty rep squat routines are very effective for legs, but the upper limit for most upper body exercises will be around 15. In either case, providing the volume is equal, reps of 15-20, 10-12, and 3-5 have been shown to result in exactly the same stimulation of muscle protein synthesis. (7) The only real difference between them (besides one obviously using lighter weights) will be with the 15 reps (obviously the higher volume protocol) you tax muscular energy stores so in addition to increasing the protein content you also get more glycogen storage. In either case the primary stimulus (work under load) is the same, the muscles activated are the same, and regardless of rep range resistance training is a supplement, not the primary event.

Best Bang For Your Buck

For growth purposes the best "bang for your buck" rep range is arguably 6-8, or about an 80-85% max load, as it gives the ideal combination of recruitment and metabolic fatigue. You get full recruitment from the first rep and enough time under load to optimize th emetabolic processes contributing to hypertrophy. Higher reps have the benefit of less joint stress while lower reps have the advantage of greater nervous system activation, and also make it easier to keep volume down and avoid growth stimulation, if that is a goal.

I don't want this to sound like I have anything against lower rep training, but there are times when it is advisable for a person to use higher reps due to injuries, age, or equipment restrictions and the practice is certainly permissible. I've known people that only had a given amount of weights at their disposal or they had injuries and were forced to train with sets of 12 or more and were able to gain just fine. My general recommendation for people over the age of 35 is to keep the reps up to 10 or more for upper body so their joints don't take such a pounding.

Don't Forget About Nutrition

Also building size is just as much about how you eat as it is how you train. You can have the perfect hypertrpohy program but it won't do anything in the absence of good nutrition. Do sets of 10-15 while eating to keep your BW constant and all you'll do is get strong, just ask many of the former HIT (high intensity training) Nazis. Do singles often enough while eating like a hoss and you'll get plenty big.



(1) Selective activation of AMPK-PGC-1alpha or PKB-TSC2-mTOR signaling can explain specific adaptive responses to endurance or resistance training-like electrical muscle stimulation. FASEB J. 2005 May;19(7):786-8. Epub 2005 Feb 16.

(2) Stimulation of human quadriceps protein synthesis after strenuous exercise: no effects of varying intensity between 60 and 90% of one repetition maximum (1RM). J Physiol 547.P, P16.

(3) No effect of creatine supplementation on human myofibrillar and sarcoplasmic protein synthesis after resistance exercise. Am J Physiol Endocrinol Metab. 2003 Nov;285(5):E1089-94.

(4)Coordinated collagen and muscle protein synthesis in human patella tendon and quadriceps muscle after exercise.J Physiol. 2005 Sep 15;567(Pt 3):1021-33.

(5)Protein synthesis rates in human muscles: neither anatomical location nor fibre-type composition are major determinants. J Physiol. 2005 Feb 15;563(Pt 1):203-11. Epub 2004 Dec 20.

(6) Skeletal muscle hypertrophy and structure and function of skeletal muscle fibres in male body builders.

(7) Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones.Eur J Appl Physiol. 2002 Nov;88(1-2):50-60. Epub 2002 Aug 15.