When I first started training, there was a pervasive idea in the world of fitness that light weights improve tone.
A lot of women are still caught up in this idea, high reps, low weight, burn calories and improve this vague concept of ‘tone.’
The problem with that statement is what ‘tone’ really means.
Muscle tone is really the shape of a muscle revealed below by low body fat percentage.
Meaning you’re either shaping/building muscle below your skin to improve it’s tone once you’ve dieted down lean enough to see it easily.
Or your trying to preserve the muscle shape below, while using mostly dietary changes (negative energy balance) to reveal what muscle shape you already have underneath.
Lost in all the mix is the pervasive notion that one way of lifting is better than another. Is it that black and white?
Muscle Fiber Types
Let’s get this little discussion out of the way to help paint a clearer picture.
A lot of people use this discussion for pro-light weight or pro-heavy weight discussions.
One camp will say that low load training yields more type 1 growth, which don’t have a ton of natural ability for an increase in size.
This might be an perceived advantage to people who want to ‘tone’ and don’t want to build because any muscle built would be theoretically lower.
The other camp might say due to that, if you want to build muscle, you shouldn’t use any low load, high repetition training because it only builds type 1 fibers.
They might gear you toward high load, low rep training instead, because if low load, high rep training only builds type 1 fibers, then surely heavy weight training is the opposite?
But is that true?
Currently we acknowledge there are two main kinds of muscle fibers:
- Type I (1) Aerobic or Highly Fatigue Resistant Fibers
- Type II (2) Anaerobic or Not that Fatigue Resistant Fibers
It’s not exactly this simplistic, but it was generally thought that low load, high rep training would train more type 1 and by extension high load, low rep training should train more type 2.
You could likely make a good argument that there are certain low threshold predominantly type 1 muscles or muscle groups (like the neck or some of the torso muscles) that are such low threshold that hypertrophy here is next to impossible.
There likely exists some sort of spectrum within type 1 fibers, which just don’t know how that operates at present.
There are really 3 different subtypes of Type 2 fibers worth considering:
- Type IIa (more oxidative than the other two)
- Type IIx (likely transitionary fibers)
- Type IIb (most anaerobic, biggest, strongest)
That we know of…
I’ve seen papers with type IId and other abbreviations, so the jury is still out a bit.
Type IIb are the stronger, fastest, biggest but also the most prone to fatigue.
There is a great deal of debate into how to develop type IIb.
Most of what I’ve read so far indicates either heavy eccentric training or speed training with light loads. Even then, the evidence seems weak.
Detraining of all things seems to change the percentage best of distribution towards type 2b. Counterproductive, given what they can do but it’s the best answer I currently have.
There is a lot of speculation and what I can say is that a lot of that speculation is wrong.
People want type 2b development for power sports so they lift really heavy (<5 reps) or they do power training really heavy (<6 reps with speed — think olympic lifts or something similar) or they think plyometrics can yield type IIb.
None of those things seem to dramatically influence type 2b development and maybe this is one of those things that is more about your genetics. I can’t say yet.
Low rep, high load training, does not actually build the biggest muscle fibers — Type IIB — contrary to the assumption many people make.
Let’s ignore type 2b for now, because it’s over most people’s heads, including mine. No research I’m aware of at the moment has given us clear guidelines on how to train for that.
I’m not saying how you train can’t or won’t influence muscle fiber type distributions but I’m not convinced it’s how many people believe.
Henneman’s Size Principle
We’re still figuring out how different rep ranges manipulate the type of muscle built and there is likely a bit of a spectrum to consider.
It’s not as simple as light weight training develops type 1 fibers, and really heavy weights develop type 2b fibers, as many people appear to believe.
It turns out that most research so far indicates that lifting weights does yield more type 2 fibers, but it’s traditionally more type 2a fibers. Likely type 2a fibers transitioning from type 2x fibers.
All types of resistance training appear to have this effect to some extent, whether it’s high load or high rep training.
Due to a principle called ‘Henneman’s Size Principle.’ This principle basically states that muscle fiber units are recruited in order of size based on the stimulus.
Bigger and bigger motor units are always recruited as they are needed.
So you lift something light or easy, you might recruit the smallest muscle fiber unit necessary. i.e. motor units that consist more of type 1 fibers.
This is energy conservation at it’s finest. No need to turn on big muscle fiber units when the weight is nothing.
When you lift something at 80-85% 1RM (~5-7 reps or less), almost all of those muscle fiber units appear to be activated. Which can be another reason people might advocate for exclusively lower rep training.
*I’ll get to why that might not always be the best approach in a moment.
What’s often missed, is that even with high rep training, you can still end up stimulating those same motor unit fibers. If you reach high enough levels of fatigue.
Yes, even low load, high rep work, can develop muscle in a very similar fashion when it comes to the type 2a fibers I mentioned above.
Yes, there is a spectrum still and there are other potential types of hypertrophy I’ll get to, but so long as you lift to a point of enough mechanical tension, for enough volume of exercise, all rep ranges seems to result in a similar outcome.
Meaning all rep ranges are really the ‘hypertrophy zone‘ if they are utilized appropriately.
**Hypertrophy is just a fancy word implying growth/expansion or ‘an increase in volume,’ and is essentially the opposite of ‘atrophy.’
Well likely anything between about 1-25 or 1-30 reps anyway. With less absolute failure (total fatigue) being required closer to 1 (but also far more sets) and more absolute failure being required closer to 25 or 30.
There appears to be a cutoff around 30-40% 1RM (click that link if you don’t know what that means) in terms of the lowest tolerable load for stimulating growth.
Unless you cut the blood supply off with blood flow restriction training but that’s neither here, nor there. As it’s not that viable an approach to training unless you’re injured.
Now there is some indication that using a variety of rep ranges is beneficial in your training, even if your goal is muscle growth (AKA hypertrophy).
However, it appears the rationale for that is actually different.
Types of Hypertrophy
In order to understand this all, you have to understand that there are generally acknowledged two completely different types of “muscle hypertrophy.”
- Sarcoplasmic Hypertrophy
- Sarcomere or Myofibril Hypertrophy
AKA Non-Functional Hypertrophy. Indicates the sarcoplasm surrounding the muscle increases more in volume.
The the cross-sectional area of a muscle increases but the muscle fibers themselves might elicit little to no actual gain in size.
This more likely happens when you lift at moderate to higher rep ranges (>8 reps).
Hence you’re most likely to see it present in sumo wrestlers and bodybuilders.
This is often generally acknowledged not to last as long. The theory being that the organelles and other structures floating in the sarcoplasma can more easily deteriorate than actual muscle growth would in theory.
However, I’m not 100% sure that’s true and it’s possible we’ve over simplified this.
AKA Functional Hypertrophy. This appears to be a more visible change in the muscle cross sectional area. Rather than the fluids surrounding the muscle fibers.
This is likely more of what you’d see in powerlifters or Olympic lifters and other high intensity, low rep sports — power sport athletes, like most people from all walks of life, would be better served by going after this type of hypertrophy.
Thought to be more associated with <8 rep ranges. It’s not muscle fiber changes necessarily, but rather the type of hypertrophy that different rep ranges might influence.
Debate and Reality
Of course this is all highly debated in the fitness world. It’s possible sarcoplasmic hypertrophy is more of a direct result of measuring muscle thickness too close to training.
When you train, you increase sarcoplasmic volume with nutrients for recovery. It’s possible the appearance of sarcoplasmic changes is a side effect of researchers not waiting long enough before measuring. Giving the opportunity for those nutrients to clear (usually within about 72-96 hours).
On the other hand, I’m not convinced that the two types of hypertrophy are mutually exclusive anyway.
There is no guarantee near as I can tell that you’ll only build functional hypertrophy if you lift heavy, and more sarcoplasmic non-functional hypertrophy if you lift lighter.
It’s likely that you build more myofibril volume with lower rep, high load training, but some sarcoplasmic hypertrophy is going to come along for the ride. And vice versa.
There is a third (and fourth type) of hypertrophy that is generally dismissed in humans.
Hyperplasia – a highly debated phenomenon whereby muscle fibers actually split apart into new fibers.
It has been shown to occur (particularly in cats and other animals) and maybe it does occur in human beings too (we’re just not going to cut up human beings, to really take a look, ya know?).
It’s again observed that there are two types:
- Sarcoplasmic Hyperplasia (whereby organelles in the sarcoplasm increase in number)
- Myofibrillar-Mitochondrial Hyperplasia (which notes an increase the mitochondria of the muscle cells and the number of myofibrils within a muscle)
Best bet is that #1 does occur. #2 well that’s the more debated phenomenon.
Were this type of hypertrophy to take place — and it’s possible — you would in theory have a very difficult time losing any muscle mass once this type of muscle has been built.
Meaning it might mimic sarcomere or myofibril hypertrophy.
What Else Influences Hypertrophy?
I used to think it was that simple, but newer research and some insights from a colleague have broadened my perspective.
Different types of lifting do influence development or growth and outcomes in different ways. It just has nothing to do with fiber types.
There are a few new-ish considerations we can make:
- Type of Resistance
- Range of Movement
- Contraction Type
- Regional Hypertrophy
Type of Resistance
Using free weights, or a constant load (meaning the weight is the same through the entire range) might yield more hypertrophy towards the end of a muscle. *Called the distal part of the muscle.
While an accommodating resistance (like using bands or using chains) might yield more stress at short muscle lengths because the stress is stronger when you’re stronger and lower where you’re weaker.
Leading to more growth in the muscle belly. We need more data, but it’s possible.
This indicates that in the long-term a mix of heavy full range lifting, could lead to a different type of muscle growth, from say low load, high rep band training.
Range of Motion
You’ve seen that dude in the gym doing the quarter squats. We all have.
And while, it’d be easy for all of us to hate on him, he may be onto something if he wants more hypertrophy towards the middle of the muscle belly.
When you don’t take muscles to long lengths, they appear to develop more hypertrophy towards the middle of the muscle. Full range training takes muscles to long lengths.
I generally lean towards full range of motion for most people, but this may provide a strong case for doing some partial range work with heavier loads from time to time.
That is, if you desire more muscle hypertrophy towards the middle of the muscle, maybe partials aren’t so bad afterall.
This could indicate that some low rep, high weight, short range movements might yield different hypertrophy than lower load (longer ranges of motion need lower loads) fuller range movements.
It isn’t the rep range per say that matters then. Maybe it’s other things?
Eccentric training as a type seems to increase the length of of the fascicle, as opposed to the thickness. Meaning that you might get growth increases in the length of a muscle, or towards the outer parts of the muscle closer to the tendons.
This could be especially valuable for injury prevention as it improves the muscles ability to tolerate stretch.
Concentric training however, seems to have a somewhat different effect.
Something about this contraction mode seems to favour growth increases in thickness, especially within the middle or belly of the muscle.
I’m not sure this has a ton of total relevance you don’t see as much or as quick muscle development when using predominantly concentric muscle actions.
However, once more it’s not the rep range per say that may matter. You’ll likely need more volume with concentric focused training, hence more reps, but you may get a different kind of hypertrophy as a result.
A last consideration is that different muscles have different motor units. The glutes have four distinct muscle motor units. The shoulders have at least 3, the pecs have at least 3.
These are reasons why people recommend doing shoulder specific actions for the front, middle and back parts of the shoulders.
OR why people recommend doing incline, flat and decline bench press to favour the different motor units of that muscle.
All this really implies is that you likely want some variety in your training to maximally stimulate muscles from a spectrum of positions.
It’s generally impossible to always be training, all of these different qualities, given the shear number of exercises available to you.
Nor does it imply that the upper fibers or lower fibers of the pec aren’t doing anything during flat bench. They are. The same is true for most muscles.
Again this doesn’t have anything specific to do with rep ranges other than some exercises tend to lend themselves to certain rep ranges.
Leg press can be loaded heavily to moderately or even rather lightly. Leg extensions or curls, not so much variability because of long lever lengths.
Doing high rep squats or deadlifts is usually waiting for something to go wrong. Only highly advanced trainees should really be using exercises like that for high rep ranges.
Likewise it doesn’t make much sense to do 2-3 reps of flies, or direct shoulder work (lateral, anterior or reverse fly) don’t lend themselves to high load, low rep training as you might not even be able to get the weights up at all.
You’re going to hurt yourself with long lever exercises for anything heavier than a moderate (8ish+) rep range.
Most of the time, you want to choose rep ranges based on practicality of the exercise you’re using. In addition to the part of the muscle you may or may not be stimulating.
What If You Don’t Care About Hypertrophy?
That middle section of this article is a bit of a tangent. It makes it seem like all we want to do with rep ranges is develop hypertrophy and this obviously isn’t true.
It’s just what I expect most people want to get out of resistance training generally speaking.
They want to look better naked. More ‘toned,’ and the best way to do that is build the muscle underneath (and get lean enough to show them off).
Not everyone cares about that. Plenty of people want to get strong without much hypertrophy (growth).
Maybe it’s because they don’t want to bulk up, or they participate in a weight class sport where being as strong/light as possible is ideal.
In this case, the general idea is simple:
Don’t train near absolute muscle failure. In fact, about 4-5 reps off or more from absolute failure is probably ideal.
For example, lift a weight you can lift 8 times, if you were training to failure, but only lift it 3-4 times instead. Keep the volume low-ish (2-3 sets) and you’ll be good. Relatively light weights, lifted quickly and not to failure.
This is the basis of velocity based strength training. Which is something we often apply to the world of athletics these days and as I indicated earlier may help at least preserve type IIb fibers (maybe help develop).
You’ll still get strong, especially with lower rep ranges, but you won’t achieve enough mechanical tension to stimulate a lot of muscle growth.
I’d be lying if I said the two were totally mutually exclusive, but this approach will be slower for muscle hypertrophy.
Especially if you’re not fueling the process with a surplus of energy and protein. Without energy/protein there is nothing to build muscle with.
So if you train and eat at maintenance or even under eat (which will limit strength gains to some degree for one reason or another), it’s unlikely you’ll build much muscle at all.
Please keep in mind: there is nothing inherently better about lifting weights to high repetitions for the purposes of avoiding muscle growth.
It’s probably a bad idea if you want to improve sport performance, get strong, and improve nervous system functioning.
Low load, high rep training doesn’t yield much improvements in those areas. If you don’t train near failure you often won’t get as much of the muscular endurance benefits either because you’re not fatiguing the muscle enough.
Contrary to popular opinion then, low load training isn’t better for people who want to ‘tone’ or don’t want to ‘bulk.’
Other Non-Hypertrophy Considerations
Lifting fast, with more predominant concentric focus, could yield something similar. You’ll reduce muscle soreness with such a strategy at the very least.
Sled work is amazing for this. You only pull or push, with no eccentric action to follow because the sled stops.
Isometrics also have a similar effect. Without the change in muscle length, you don’t get much if any hypertrophy. And you can still train isometrics explosively, which can be used very effectively in athletics.
If you use a fixed immovable position and try to move through it as quickly as possible, you can develop explosive strength, without building much muscle because there was no change in muscle length.
However, neither will necessarily improve your injury resistance, as say eccentric training appears to.
Ultimately all of that to say that rep ranges might be a little less important than some people think in the grand scheme. However, a variety is likely best.
Conclusion: Heavy or Light Weights?
Based on the above, I’m sure a lot of people are concluding high load, low rep training is better.
The problem with doing that all the time is that plenty of long lever exercises don’t lend themselves to that kind of lifting.
Constant high load, low rep training also tends to beat up on people’s joints more than moderate or low load training. It’s not as sustainable as more moderate or lighter rep ranges.
While others may still be convinced that lifting light weights for high repetitions means that you will get more toned, this isn’t necessarily true either.
You can build muscle with light weights and improve real ‘tone’ if your proximity to absolute failure is close enough.
You may have to be closer to failure than high load, low rep training. Much closer, which is also stressful and more difficult to recover from.
The real solution?
Use a variety of rep ranges periodically in your training depending on goals.
Rep ranges are just one variable to consider.
Periodic heavy lifting has benefits. Periodic light lifting has benefits. Moderate lifting provides a bit of both of those benefits.
High Intensity Lifting
≤8 reps of work is generally accepted/acknowledged towards building Myofibril Hypertrophy. It’s hard to define a cutoff though, ≤6 reps could be more appropriate.
More importantly — particularly for women — this is the rep range responsible for the greatest increases in bone density. A key determining factor in osteoporosis prevention and other health markers.
Doing some work in this rep range from time to time (in any given year) is really the only way to dramatically improve strength.
Although there are other considerations like eccentric strength, which is ideally trained in this rep range.
Anything under 3-4 increases the number of sets a person would have to use to achieve similar hypertrophy results to more moderate rep ranges. Meaning it’s generally less efficient in that role.
Moderate Intensity Lifting
This rep range will generally fall somewhere between 5-15 repetitions. More likely I’d say 6-12 reps. Yes, there is some overlap, there are no clean breaks.
This is the most efficient rep range for a hypertrophy goal, which is why it gets labelled as such.
Anything above 8 reps is generally accepted/acknowledged towards building more Sarcoplasmic Hypertrophy.
Adding to the confusion that anything under about 8 reps is ‘strength’ training. That would imply that anything over 8 reps does very little for strength.
That’s largely true but this is a good all around rep range for a lot of people. That 6-8 rep range especially for large compound movements and maybe 8-10 or 8-12 is really good for a lot of other accessory or isolation movements.
The most practical range for muscle growth objectives but deviating from this rep range periodically (for low or high intensity lifting) has benefits.
Low Intensity Lifting
Something in the neighbourhood of 12-15+ reps develops mitochondria and fatigue resistance of a muscle, particularly skewed to Type I, predominantly aerobic fibers.
However it appears that type IIa oxidative fibers can be stimulated with this rep range and hypertrophy can certain occur.
It likely takes more total reps to reach a fatigued state with light weights and achieve a base volume of stimulating repetitions. If you care about hypertrophy (which also means ‘tone’).
Meaning high reps for hypertrophy are less efficient overall for muscle growth. You have to do a lot of reps to stimulate the big motor units.
It can be done but it’s best to use this rep range for fatigue tolerance.
All that being said, a moderate rep range 6-12 is probably the sweet spot for most people, most of the time.
However, I think it’s a mistake to stay here exclusively within a yearly overview.
Some strength work (≤6 reps) has benefits not as strongly achieved with the moderate rep range.
Likewise, some endurance work( ≥12 reps) has benefits not as strongly achieved in a moderate rep range.
I think both are also more appropriate for more intermediate to advanced lifters.
That means something like:
- 1-2 months moderate rep range
- 1 month of high intensity rep range
- 1-2 months of moderate rep range
- 1 month of low intensity rep range
Or once you have a decent base of training you can put that variety within the training month:
- ~2 days a week moderate rep range
- 1 day of high intensity rep range
- ~2 days a week of moderate rep range
- 1 day a week of low intensity rep range
If you have more specific goals, then skew more to strength or endurance if you want. Most of your accessory isolation work, will likely stay in that 6-12 rep range, because it’s most appropriate for those types of lifts.
Otherwise, lift a wide variety of rep ranges from high to medium to low intensity at various times in your program for maximum results in pretty much any pursuit.
Plus it’s a good way to keep yourself engaged and interested in your program.
Also published on Medium.