Contrary to a lot of the training advice out there, you can and will gain muscle using higher reps.
Back in 2012, researchers from McMaster University got a group of guys to train their legs on the leg extension machine three times a week for 10 weeks, using one of three different set and rep configurations :
- 1 set of 10-12 reps performed to voluntary failure
- 3 sets of 10-12 reps performed to the point of fatigue
- 3 sets of 30-40 reps performed to the point of fatigue
The figure below shows the change in the size of the quadriceps, measured using magnetic resonance imaging. As you can see, high reps and light weights (30%-3) stimulated just as much muscle growth as heavy weights and low reps (80%-3).
Of course, these are the results from just one study. As I’ve explained in The Sherlock Holmes Guide to Separating Fitness Fact from Fiction, drawing conclusions about anything from the findings of one study is never a good idea.
However, it’s not a single, lone piece of information that contradicts a large amount of existing research on the subject.
In fact, there are plenty of other studies out there showing multiple benefits of high rep training.
- Light slow-speed training (55-60% of 1-RM, 3 seconds for eccentric and concentric actions) has been shown to increase both muscle thickness and maximal strength . The results are comparable to those obtained with heavy normal-speed training (80-90% of 1-RM, 1 second for concentric and eccentric actions).
- Both heavy (4 sets of 8-10 reps with 80-85% of 1-RM) and light training (4 sets of 18-20 reps with 65% of 1-RM) activate the expression of various genes involved in muscle growth .
- Eight weeks of training the arms with light weights (20 rep-max) and short (30 seconds) rest periods led to gains in size that were not significantly different to those seen with heavier weights (8 rep-max) and longer (3 minute) rest periods .
- Light training (not done to failure) also stimulates protein synthesis in connective tissue just as well as heavy training, giving it a role during injury rehabilitation to improve regeneration of connective tissue .
High Reps For Muscle Growth: For Beginners Only?
One of the main criticisms of many of these studies is the fact they use untrained beginners, who tend to grow no matter what they do.
But even in guys with several years of lifting behind them, higher reps and lighter weights still do a surprisingly good job at adding size.
In another study from McMaster University, a group of 49 men in their early twenties was assigned to one of two groups . The high rep group did 20-25 repetitions per set, while the low rep group did 8-12 repetitions per set.
The men were all in their early twenties, and had been lifting weights for an average of four years.
After 12 weeks, there was no statistically significant difference in the rate of muscle growth between the two groups.
However, that doesn’t mean the two protocols delivered identical results. The average muscle gain in the high rep group was 2.2 pounds (1 kilogram), compared with 3.5 pounds (1.6 kilograms) in the low rep group.
Had the study lasted longer, the difference in results between the two groups may have become large enough to cross the statistically significant threshold.
What’s also interesting is that both the slow and fast twitch muscle fibers grew to a similar extent in both the high and low rep groups.
The muscles in your body consist of thousands of tiny muscle fibers. These fibers are classed broadly as either fast twitch or slow twitch.
Your body recruits muscle fibers based on the force demands placed upon it. Lift a heavy weight once, and the force requirements are a lot higher. So your body taps into the fast twitch muscle fibers.
Lift a light weight once, and your muscles don’t need to produce a great deal of force. So your body does just enough to get the job done, and calls the slow twitch muscle fibers into action.
But lifting heavier weights isn’t the only way to recruit the fast twitch muscle fibers. Fatigue also plays an important role.
Carry on lifting that light weight, and eventually those slow twitch fibers are going to get tired. So your body calls on the fast twitch fibers that have previously been held in reserve.
This recruitment process explains why the slow and fast twitch muscle fibers grew at about the same rate in both groups, irrespective of the weight or number of reps.
A study set up along very similar lines, this time lasting eight weeks, led to much the same results .
Training with higher reps and lighter weights (3 sets of 25-35 reps to failure) led to gains in muscle size that were on par with heavier training (3 sets of 8-12 reps to failure), even in guys who have moved past the beginner stages of training.
However, the fact that it’s possible to build muscle using higher reps and lighter weights doesn’t necessarily mean that it’s a good idea to do so.
Remember, there were no discernible advantages to the high rep protocols. They didn’t lead to superior gains in size or strength. But each set took twice as long to complete.
Training to failure in a higher rep range is also highly unpleasant and extremely painful – a lot harder than lower reps and heavier weights.
Doing longer, more painful workouts simply to generate the same results doesn’t sound like a great idea to me.
Two Types of Muscle Growth
Some say that the type of muscle growth caused by training with higher reps and lighter weights isn’t as “good” as you get with heavier weights.
Here’s what they’re talking about.
If you could take a closer look at a slice of muscle tissue, you’d see that it’s made up of many smaller muscle fibers. Your muscles get bigger when these individual fibers become thicker, a process known as hypertrophy.
Inside each fiber are rod-like structures called myofibrils, which run parallel to one another. Myofibrils are the part of the muscle that contribute to force production.
There is also a fluid part of the muscle fiber, known as the sarcoplasm, in which the myofibrils are embedded. It’s filled with stuff – such as water, glycogen, and myoglobin – that doesn’t contribute directly to the production of muscle force.
The term myofibrillar hypertrophy refers to an increase in the volume of the myofibrils, while sarcoplasmic hypertrophy describes the expansion of the sarcoplasm.
The idea is that doing higher reps with lighter weights leads mainly to so-called “non-functional” sarcoplasmic hypertrophy, creating “puffy” muscles that tend to deflate relatively quickly.
Training with heavy weights and lower reps, on the other hand, is said to preferentially increase the rate of myofibrillar hypertrophy, leading to dense, strong, “functional” muscles.
That’s the theory, anyway. Personally, I’m not convinced.
In one of the few studies to compare the effect of high versus low repetitions on myofibrillar and sarcoplasmic protein synthesis, low load training did increase the rate of sarcoplasmic protein synthesis to a greater extent than heavier training .
But it increased the rate of myofibrillar protein synthesis too.
Interestingly enough, when it was measured 24 hours after exercise, high reps and light weights (4 sets of 24 reps) increased myofibrillar protein synthesis to a far greater extent than low reps and heavy weights (4 sets of 5 reps).
Granted, this study looked at short-term changes in protein synthesis after exercise, rather than long-term changes in muscle tissue after several months of training. We can’t assume that the former is a completely dependable way to predict the latter.
But it does paint a big question mark next to the idea that lighter weights and higher repetitions will preferentially increase sarcoplasmic rather than myofibrillar hypertrophy.
This doesn’t mean that training programs built on the sarcoplasmic versus myofibrillar hypertrophy concept don’t work. Just that the way in which they’re supposed to work is probably wrong.
The sarcoplasm exists. It can grow.
But there’s no convincing evidence to suggest that the muscle growth produced by training with lighter weights and higher repetitions comes predominantly from “non-functional” sarcoplasmic hypertrophy, while the myofibrillar component of the muscle remains the same size, or grows to a much lesser degree.
If you want to add muscle mass as fast as your genetics will allow, lifting heavy weights should still be the main focus of your training. But the addition of some high rep work to a program that already includes heavier training is a great way to get bigger and stronger.
In summary, you can build muscle with low reps. You can also build muscle with high reps. For best results, I think it’s a good idea to do both.
SEE ALSO: THE MUSCLE BUILDING CHEAT SHEET
If you're fed up spending hours in the gym with nothing to show for it, then check out The Muscle Building Cheat Sheet.
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ABOUT CHRISTIAN FINNChristian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.