You know how it is.
Low reps mostly build strength. High reps mostly build endurance. Six to fifteen reps, that’s where it’s at for building muscle, everyone will tell you.
But you can’t help wondering.
Why are weight lifters so big then? Why are some of the biggest guys in the gym always busting out using high reps? Why are they bigger then you?
Do you just need to be patient, or could it be, that really, you’ve been doing it wrong all along?
Muscles Work According the Size Principle
Your muscles consist out of lots of muscle fibers. These muscle fibers come in different sizes, from small to big.
Small muscle fibers cannot produce much force but have great stamina. In contrast, big muscle fibers produce a lot of force but fatigue fast.
These muscle fibers can contract to contract the muscle they are part of. The more muscle fibers contract, the stronger the contraction of the muscle.
So when you lift a low weight, you only need to use a few small muscle fibers.
But when the muscle needs to produce more force, more and bigger muscle fibers are needed. Thus, lifting a heavy weight recruits many more muscle fibers than lifting a small weight.
And the more muscle fibers you use, the bigger the training stimulus is.
But does lifting a heavy weight always use more muscle fibers than a low weight?
Weight Versus Reps
There is a drawback to lifting heavy weight compared to low weight though.
You cannot lift a heavy weight as many times as you would a lower weight.
So why is this, and why does it matter?
When you lift a heavy weight, all your muscle fibers are contracting to produce force. But after a few reps, the big muscle fibers are fatigued and cannot contract anymore. As a result, you cannot contract your muscle hard enough anymore to lift the weight. This is what is called failure; the point where you cannot perform another rep.
So what happens when you lift a lighter weight?
Initially you’ll only need to use a few small muscle fibers. But as you continue to bust our reps, these muscle fibers start to fatigue. This forces the other (bigger) muscle fibers will take over. These will eventually fatigue as well, and this is when you’ll reach failure, albeit at a much greater rep count.
Thus, as long as you train until failure, you activate and fatigue all your muscle fibers and give a maximal growth stimulus to your muscle. Whether you do this with a heavy weight for low reps or with a low weight for high reps, should not matter in theory…
Burd and his collegeas from the McMaster University performed a study to measure the effect of high reps and low reps compared on muscle growth.
First, the subjects where tested for the maximal weight they could lift one time. This is called their 1 repetition max (1RM). This 1RM was subsequently used to determine the weights to be used in the study.
Three different training protocols were tested:
- 90% of 1RM to failure (90FAIL)
- 30% of 1RM to failure (30FAIL)
- 30% of 1RM work matched with 90FAIL (30WM)
So the first protocol uses a heavy weight for low reps (90FAIL) and one protocol that uses a low weight for high reps (30FAIL). In the third protocol, also a low weight was used, but the set was ended when the subjects performed the same amount of work (number of reps times the weight ) was reached as in 90FAIL.
Muscular Failure Triggers Early Peak in Muscle Growth
Burd found that that 90FAIL and 30FAIL protocols resulted in similar increases in myofibrillar FSR (a marker for muscle growth) four hours after the training. However, the 30WM protocol had a smaller increase.
So the two groups that lifted until failure had the same growth response and this response was greater than in the group that did not lift until failure.
This shows that lifting until failure is essential to maximally stimulate the muscle growth response in the early hours after training.
In addition, it doesn’t matter how failure is reached. This can be done by a height weight for a few reps, or by a lower reps for more reps.
Amount of Work Determines Duration of Muscle Growth
Burd also measured what happened 24 hours after the protocols.
Interestingly, twenty four hours after the training, 30FAIL had the greatest rate of muscle growth. 90FAIL and 30WM both had lower rates that were similair to each other.
These responses parallel the amount of work performed in each protocol.
90FAIL and 30WM were designed to perform the same amount of work, and their rate of muscle growth was similair 24 hours after the exercise.
30FAIL was the protocol with the greatest amount of work, and resulted in the greates rate of muscle growth the day after.
This shows that the amount of work is an important in determining the duration of the growth response.
Muscular Recruitment and Total Work are the Muscle Growth Triggers
So what does this study teach us?
It shows us that there are two important muscle growth signals.
The first growth signal is muscular recruitment, how much of your muscle fibers are used in a set. This is maximized by lifting until failure.
Now I’m not telling you to lift every set until failure, which a lot of people find mentally exhausting (aka overtraining), but realize that you should lift at least until reps become difficult to perform. Otherwise, you’ll miss out on the early peak in muscle growth after your training.
The other muscle growth signal is total work. If your total amount of work in the gym is higher, your growth response will be longer.
Simply perform a lot of reps to boost your amount of work!
The main take away of this study is a tweetable!
Although there is some research that suggests you should change rep ranges every training session, don’t sweat it to much and just make sure you lift close to failure and perform a high total amount of work.
Now Here’s What I Want You To Do
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Now I pass it to you…
Are you planning to add high reps sets to your routine?
What is your experience with high reps ranges?