Are there different muscular adaptations between barbell and dumbbell use?

Question

Most exercises can be performed with similar weight and form using either a barbell or a pair of dumbells. I have heard that as people begin to lift heavier weights it becomes more difficult to increase the weight of dumbbells when compared to barbells.

Similarly, my gym's dumbells only go as high as 30kg, and I've noticed that while I can barbell bench press 60kg for 5 reps quite easily, I can't do the same when trying to press a 30kg dumbbell in each hand (even with help getting the dumbbells into position).

• Why is it more difficult to perform a lift with dumbbells than it is with with an equivilent weighted barbell?
• Is it because different muscles get used when being using dumbbells, even though its the same basic movement?
• If there are differences, are there any advantages to barbells over dumbbells or vice versa?

Answer 1

Pro Dumbbell

1. Allows for a more natural movement.
2. You can do more movements. Could not do flies with a bar...
3. A seasoned lifter does not need a spotter.
4. Work your fixator/balancing muscles more.
5. Force you to use each side equally. Can really help if you have a muscle imbalance.
6. Can help stress smaller muscle groups.
7. Stretches muscles better (with correct form) promoting more tendon strength.
8. Always working out your fingers, hands, wrist, and forearms.
9. Simulates athletic movements better, especially in the upper body.

Pro Barbell

1. Allows for better progression. Easy to add 2.5 lb weights to each side. We actually have 1.5 pound collars used for progression lifts at the school gym.
2. Helps focus on larger muscle groups. If you squatted with dumbbells there would be a lot of additional muscle groups supporting the weight being held.
3. Easier to use when you get to heavier weights. Loading 150lb dumbbells on your chest to do inclines is a chore. I think getting these on my chest was half the battle. Very easy to load a bar up and sit down.
4. Allows you to do more weight. If you squat 600lbs good luck finding the dumbbells you need.
5. There are certain lifts that are hard to do efficiently with dumbbells. Think cleans, snatches, good mornings, skull crushers (I hate the dummbbell version)...
6. Very expensive and takes a lot of space to do a dumbbell only solution.
7. If you do any competitions - they don't use dumbbells.
8. Dumbbells are always working out your fingers, hands, wrist, and forearms.

In almost any example your dumbbell movement (x2) will not equal your barbell movement because it puts a lot of stress on fixator muscles. I have found that your dumbbell max for the same movement is roughly 75-90% of your barbell movement. I give a range because it is very easy for some lifters who don't routinely use dumbbells to not have the range of motion or balancing muscles in place to get near 90%. Only if you are putting in the same intensity or if you have more of a dumbbell plan can you hit that 90% mark.

To give you a real world example: Grab dumbbells so that you have about 70% of your max. Lay on a bench and hold them straight out like you are top of your bench progression. See how long you can hold it there and why you fail. Then go over and do the same thing with a bar. Even at 70% of my max I can hold the bar a long long long time - where boredom might cause failure.

Answer 2

From Starting Strength:

The dumbbell version of the exercise [...] involves a greater amount of instability [...]. This is especially true if the weights used are sufficiently heavy to challenge your ability to finish the set. Most trainees use dumbbell bench presses as a light assistance movement, and never appreciate how hard they are or how useful they can be at heavy weights.

[...] the lifter has to take the dumbbells out of the rack or off the floor, get into position on the flat bench, do the set, and then get off the bench with them after finishing it.

Because dumbbells are not tied together between the hands as a barbell is, dumbbell bench presses require more active, conscious control, are harder to do, and therefore less commonly done.

The problem with dumbbell bench presses is that the equipment provides its own limitations in a progressively increasing program. Most dumbbell racks are not graduated in fine-enough increments due to the expense of having twice as many dumbbells as most gyms have the money or space for. Plate loaded dumbbell handles that would permit such loading are not widely available, or of sufficient quality that they are safe at heavy weights, or capable of being handles without a lot of help from two spotters.

And with heavy weights, getting on and off the bench becomes such a large part of the task of completing the set that the logistics are a giant pain in the ass.

[...] as good an exercise as the dumbbell bench may be, you will be bench pressing with a barbell, as the weight of history and precedent demands.

In my experience, the limiting factor at heavy dumbbell weights is the constant firing of smaller muscle groups needed to stabilize the heavy dumbbells.

Generally, improvements in these small stabilizers don't transfer into sports as much as improvement in the larger muscles. I stick with the barbell, so that I can continue strengthening the largest muscle groups in a linear progression for a long period of time without being impeded by my weaker stabilizing muscles.

The smaller muscles are still getting worked, just not as much, and I'm not letting them be the bottleneck, because that's not where the biggest return on investment is going to come from for me.