40 kg is a very good bicep curl weight if you use strict technique and perform multiple reps.
The human biceps are a lot stronger than most people think, especially when you consider the fact that a curl is a relatively easy exercise to master.
With that in mind, this guide will help you to understand why a 40 kg bicep curl is a good lift for most gym-goers. You’ll also learn if it’s possible to do a 40 kg curl with dumbbells.
See How Your Bicep Curl Stacks Up:
How impressive is a 40 kg bicep curl?
A 40 kg bicep curl is a good lift that is realistically attainable for the vast majority of natural weight lifters. While 40 kilograms isn’t extremely heavy, it’s by no means light for a relatively small muscle group like the biceps.
Of course, performing barbell curls with 40 kg is more impressive if you’re doing a higher number of reps and more quality sets. Tension and volume, after all—not one rep max strength—is what really builds the biceps. 
With this in mind, it’s actually better to do fewer reps with better form than it is to do more reps with sloppy form. In other words, more reps doesn’t necessarily equal more tension on the biceps if your technique is bad.
Nevertheless, even if you can only do a few reps, a 40 kg barbell curl is still a good lift and is definitely a major milestone for bicep strength.
Is a 40 kg dumbbell curl realistic?
While a 40 kg dumbbell curl—especially for reps—is beyond the reach of most natural lifters, that’s not to say that performing 40 kg dumbbell curls is impossible.
There are, in fact, multiple pieces of video evidence that show that curling 40 kg dumbbells is possible for those with well above average bicep strength.
Of course, 40 kg hammer curls are easier than 40 kg bicep curls because when you curl with a neutral grip, your brachialis and brachioradialis muscles, which, like the biceps, are two very powerful elbow flexors, get put in a stronger force-producing position.
40 kilogram supinated bicep curls, on the other hand, are very challenging to perform indeed. After all, if you can curl 40 kg dumbbells, then your biceps are lifting more weight than most people can bench press with their chest, triceps, and shoulders.
How about a 45 kg barbell curl?
While a 45 kg barbell curl might not seem much different from a 40 kg barbell curl, it actually is.
Going from a 40 kg bicep curl to a 45 kg bicep curl is a 12.5% increase in resistance. That’s a significant amount of weight, considering that a 40 kg curl is already an impressive lift.
As such, you likely need to be curling 40 kg for 8-12 clean reps before you can even lift 45 kg for a few hard-earned repetitions.
If 45 kilograms doesn’t sound like a particularly heavy weight, just remember that a bicep curl is a pure isolation exercise.
Yes, you do have your forearms and other elbow flexors (brachialis and brachioradialis) to help out, but even when added together, these muscles still don’t have as much force output potential as your back or legs, so 45 kg is a very decent amount of weight to curl.
40 kg bicep curl case studies
See what kind of physique and strength it takes to perform both 40 kg barbell curls and 40 kg dumbbells curls.
Case study 1: Chris Weaver
Chris Weaver managed to curl 40 kg not once, not 5 times, not 10 times, but 18 times!
What you’ll notice from the video is that Chris obviously has excellent bicep development. This just goes to show that, more than anything, your curl strength is a function of your bicep size.
It’s great to do an AMRAP set now and again if you train for hypertrophy because it’s a good way to measure your volume tolerance. And training volume, after all, which is essentially a convenient way to measure muscle tension,  is one of the primary drivers of hypertrophy.
In summary, 18 reps with 40 kg is very impressive indeed, especially considering the fact that he was using a full range of motion on every rep. That’s how you build the biceps, fellas. Form is key.
Case study 2: Danijela Hodges
If you’re a bloke who can’t curl 40 kg, look away now. Danijela Hodges managed to curl 40 kg for two textbook reps (I think she could’ve done a few more).
Danijela’s form is just about the best that you’re going to see because she really controlled the eccentric phase of her reps with every ounce of effort.
Whether or not she’s intending to bulk up her biceps or merely test her strength, Danijela’s technique is a great way to stimulate biceps hypertrophy because it provides your muscles with plenty of time under tension.
Case study 3: Jason Steenkamp
If you want to see the kind of muscularity that’s required to perform a 40 kg dumbbell curl for reps, look no further than Jason Steenkamp.
At a staggering body weight of 102 kg (staggering because he’s also shredded), Jason curled the 40s for 6 reps per arm.
These weren’t 40 kg hammer curls either; they were real 40 kg bicep curls. He supinated his wrists on every rep to train his biceps to the max. You have to wonder just how much weight this guy could handle if he wasn’t as shredded!
Conclusion: Who should be doing 40 kg bicep curls?
If you’re an intermediate lifter with good biceps, then you should be able to curl 40 kilograms for around 5-8 reps, and that’s with a barbell.
A 40 kg dumbbell curl, as you just saw, is a feat of strength that only elite lifters can attain.
This is nothing to worry about because you can already build better biceps than 95% of people by curling 40 kg strictly with a barbell.
In summary, a 40 kg bicep curl is a great lift, which is only made better by performing a higher number of reps with quality form.
- Bumgardner, T. (2020, April 24). The Basics Of Training For Size Or Strength. Bodybuilding.Com. https://www.bodybuilding.com/content/the-basics-of-training-for-size-or-strength.html
- Labrada, H. (2015, April 30). Lift For Length: Build Muscle With Time Under Tension. Bodybuilding.Com. https://www.bodybuilding.com/fun/lift-for-length-build-muscle-with-time-under-tension.html