Biceps curls are most commonly performed with weights, be it with dumbbells or barbells.
However, what if you saw an individual biceps curling without any weight?
What if I told you that this can build muscle?
I’m not just talking about a small degree of muscle growth either, rather potentially a similar amount to biceps curling with weight.
Sounds crazy right?
But let’s examine a study by Counts et al. that inspired this article.
5 men and 8 women, all previously untrained, had one arm assigned to a no-load condition and their other arm assigned to a high load condition.
Both arms were trained three times per week (on non-consecutive days) for 6 weeks.
With the arm that was assigned to the no-load condition, they performed a biceps curl with no actual weight, but they aimed to squeeze and maximally contract the biceps throughout the curling movement. They did this for 4 sets of 20 repetitions with 30 seconds of rest between sets.
Electrodes were placed on the biceps to give feedback of its activation, thereby encouraging participants to further maximally contract the muscle throughout the range of motion.
With the opposite arm assigned to the high load condition, they performed a dumbbell biceps curl with 70% of their one-repetition maximum. They did this for 4 sets of 8-12 repetitions with 90 seconds of rest between sets.
Thickness of the biceps was measured at three regions, roughly 50, 60, and 70% of the upper arm length.
What the researchers found was that at all three regions of the biceps, growth was similar between the no-load condition and high-load condition.
In other words, biceps curls with no load, but trying to squeeze and maximally activate the biceps throughout the curling motion resulted in similar gains to regular dumbbell curls.
These results are extremely interesting, before we speculate why this occurred, let’s first address some limitations.
Firstly, some may suggest that the results of this study could be explained by the cross-education effect.
For those unaware, this is where training only one side of your body, can increase the strength and size of the opposite untrained side of your body, we have a whole article dedicated to this at House of Hypertrophy.
Therefore, some may suggest the muscle growth for the no-load arm was due to the cross-education effect obtained from training their other arm with high loads.
However, muscle growth seems to be extremely little with the cross-education effect.
For instance, this study by Hubal et al. had 243 men and 342 women train only one of their bicep with unilateral preacher and concentration curls.
The trained bicep increased in cross-sectional area by an average of 18.9%. However, the untrained bicep only increased in cross-sectional area by an average of 0.2%.
Therefore, it’s highly unlikely the cross-education effect confounds the results of this study.
Moreover, as noted by Counts et al., it seems the cross-education effect is minimal or nonexistent when both sides of the body are trained with different protocols, as was done in the study.
Another potential limitation is the use of different rest interval durations. Recall the no-load arm performed 4 sets of 20 repetitions with 30 seconds of rest between sets, while the high load arm performed 4 sets of 8-12 repetitions with 90 seconds of rest between sets.
Some may suggest that the use of shorter rest intervals with the no-load arm is better for building muscle.
This is a possibility, however, this claim itself is not completely supported by the research. We have a whole article dedicated to the research on rest intervals for muscle growth.
As we noted, with isolation exercises (which is what a biceps curl is) research is conflicting on whether short or long rest intervals are better. Opposingly, with compound exercises, longer rest intervals appear to be better.
Therefore, all in all, it’s hard to say if the use of different rest intervals in this study meaningfully impacted the results.
A final and notable limitation is that this study was conducted on individuals with no previous training experience. Therefore, we can’t be certain if the results of this study can be applied to trained individuals.
Why Might No Load Biceps Curls Build Muscle?
Let us now explore the potential reason for the study’s results.
I should note that if the following reasoning is true, then the findings of this study may indeed apply to trained individuals.
Currently, mechanical tension is the best-categorized stimulus for muscle growth.
Mechanical tension is simply equal to the force generated by a muscle.
Active tension is one important component of mechanical tension. Passive tension is the other, but for this article, we can ignore passive tension.
Active tension is the force generated by the contractile units of a muscle.
To understand this, we first need to understand the basics of a muscle’s structure.
Muscles are organized in hierarchical layers. Within a whole muscle are fascicles, within fascicles are muscle fibers, and within muscle fibers are myofibrils.
Myofibrils consist of an array of sarcomeres, and sarcomeres are the contractile units of a muscle. In other words, they are what produce a muscle’s force.
More precisely, when something called the myosin head, extends from the myosin filament and pulls on something called the actin filament towards the M-line, the sarcomere shortens and generates force.
Something called mechanosensors detects this force and goes on to initiate a signaling cascade that results in muscle growth.
Zooming out, we can see that high levels of active tension is a result of two components: the number of muscle fibers recruited and the amount of force generated by these recruited muscle fibers.
A high number of muscle fibers recruited means more sarcomeres are generating force, while a higher amount of force generated by these recruited muscle fibers means the sarcomeres are generating a high amount of force.
When training conventionally with weights, as you get closer and closer to failure (the point at which you cannot perform any more repetitions with a given weight), the number of muscle fibers recruited, as well as the force generated by some recruited muscle fibers increases.
Therefore, getting close to failure with a given weight creates high levels of active tension. As a side note, this is likely why both heavy and light loads can produce similar muscle growth, as discussed in other articles at House of Hypertrophy.
Now, here’s the main point, you can likely achieve high levels of active tension without any weight.
By simply moving a muscle through a range of motion while simultaneously trying to maximally contract and squeeze the muscle, you are forcing the recruitment of many muscle fibers as well as high force production by many muscle fibers. Put differently, you are self-inducing high levels of active tension.
Perhaps this explains why no-load bicep curls may be as effective as normal bicep curls with weights.
This brings up a fascinating question: are weights (or any other kind of external resistance) even needed to achieve optimal muscle growth?
If performing exercises where you simply maximally contract and squeeze a muscle throughout a range of motion provides a sufficient muscle-building stimulus, perhaps external resistances are not needed.
Of course, it’s essential to recognize the thoughts above are based on a single study. This is anything but definitive and overwhelming evidence.
Hopefully, we get more research in the future exploring this further, so we can truly gain a greater understanding of how effective this may be, especially in trained individuals.
Finally, it’s worth mentioning that maximally contracting and squeezing a muscle through a range of motion is far from easy. Remember, you’re trying to produce as much force with the muscle as possible.
In the Counts et al. study, it seems much of the subjects found that with a few of the sets, no-load training was harder and more uncomfortable than training with the dumbbell.
I highly recommend anyone to try out no-load training at least once, I think you’ll notice how challenging it can be. Additionally, you may even notice quite a decent pump.
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