Traditionally, the conventional, straight bar deadlift has always been a key exercise in strength and conditioning programs. However, many strength coaches are now programming the hex bar deadlift variation instead.
While it is tempting to consider the two deadlift variations as being interchangeable, the research indicates that there are important differences between them, which need to be taken into consideration when programming.
Here is a summary of the differences, and the practical implications.
When we watch lifters perform a hex bar deadlift, we can see that their body position differs from when they use a straight bar, particularly at the point of lift-off from the ground.
When this was assessed by researchers, one study reported that the trunk, hip and ankle angles at lift-off were not actually significantly different between deadlift variations, but knee flexion was greater (the knee was more bent) with a hex bar than with a straight bar (79 vs. 73 degrees). Another study reported no differences between variations at any joint.
This greater knee flexion makes the hex bar deadlift look more like a squat than the straight bar deadlift.
While there were no significant differences in the other joint angles, hex bar deadlift does often seem to involve a more upright trunk position than the straight bar deadlift, even though the height of the barbell from the ground is the same. Indeed, the study above reported that trunk angle tended to be slightly greater (the torso was more upright) with the hex bar than with the straight bar (58 vs. 55 degrees).
This makes sense, since the greater knee flexion (the knee is more bent) in the hex bar deadlift variation brings the hips closer to the ground, tilting the trunk more upright, and making the exercise look more like a squat.
Weight on the bar
Anecdotally, many people find that they can lift a heavier weight when using the hex bar to deadlift, compared to the straight bar, even when the height of the barbell is the same distance from the ground.
While the literature is not completely consistent on this point, it does provide some support.
The first study tested a group of powerlifters, and found that they could lift a heavier load with the hex bar (265 ± 41 vs. 245 ± 39kg). In contrast, the second study in recreationally-trained subjects did not find any differences in 1RM with a hex bar and a straight bar (181 ± 27 vs. 181 ± 28kg). However, the third study in strength-trained subjects reported a heavier load for the hex bar deadlift variation (194 ± 20 vs. 183 ± 22kg).
Even so, it seems likely that the hex bar does allow heavier weights to be lifted, because the design of the barbell allows the lifter to position its center of mass closer to their joints throughout the lift, which reduces the leverage of the barbell on the joint centers and therefore the muscle forces that are required for any given weight.
Practically speaking, when training for maximum strength, this means that the hex bar may require a greater supporting role of the upper body and grip than the straight bar, since a heavier weight will need to be supported to use the same relative load, and thereby achieve the same adaptations.
Speaking of leverages, one study measured the external moment arm lengths of the barbell at each joint (lumbosacral, hip, knee and ankle). The external moment arm length is the horizontal distance between the barbell center of mass, and the joint center.
When we lift a weight, the muscle force produced is used to create a joint moment, or turning force. This moment must equal the external moment produced by the barbell. The external moment is equal to the weight of the barbell, multiplied by the external moment arm length.
In other words, when the barbell is a long way (horizontally) from our joint, we experience the weight as being very heavy. But when the barbell is close to our body, it feels much lighter. This is why dumbbell lateral raises feel very easy at the start of the movement, but are nearly impossible to keep in the air at the end.
The study found that the lumbosacral, hip, and ankle external moment arm lengths were not significantly different between the hex bar and straight bar deadlift variations. However, they were generally longer in the straight bar than in the hex bar at the spine (21.0 vs. 14.4cm), hip (21.4 vs. 14.5cm), and ankle (16.5 vs. 11.9cm), which helps explain why the hex bar allows heavier weights to be lifted.
In contrast, the knee external moment arm length differed substantially between deadlift variations, being +8.4cm in the straight bar deadlift and -1.9cm in the hex bar deadlift.
The positive value with a straight bar, and the negative value with the hex bar indicates that, at the point of the measurement, the barbell was trying to extend the knee in the straight bar deadlift, but flex the knee in the hex bar deadlift. This implies that the straight bar deadlift will require the hamstrings to be working harder than the quadriceps, while the hex bar will require the quadriceps to be working harder than the hamstrings.
Prime mover muscle groups
Based on the leverages, we might expect the hex bar to involve greater knee moments and higher quadriceps activation, but smaller spine and hip moments and lower erector spinae and hamstrings activation.
Indeed, this is what has been found in the literature.
This study found lower peak moments at the lumbar spine, hip, and ankle in the hex bar deadlift, but an increased peak moment at the knee. And this study reported significantly greater muscle activation in the vastus lateralis, but less muscle activation in the biceps femoris and the erector spinae for the hex bar variation compared to the straight bar variation.
This indicates that the hex bar deadlift is more quad-dominant than the straight bar deadlift, and may not be as effective as the straight bar deadlift variation for training the hip extensors. Equally, it is quite likely to involve less loading on the low back.
External force, bar speed, and power
Three studies (one, two, three) have now shown that the hex bar deadlift involves greater force, bar speed, and peak power outputs compared to the conventional straight bar deadlift. However, one study has reported no differences in force between deadlift variations.
This discrepancy underscores the general trend, which is that the differences in bar speed (and therefore power) are greater between deadlift variations than the difference in force. The substantially faster bar speed may occur for several reasons.
Firstly, the greater knee flexion at the point of lift-off may mean that the joints move through a greater range of motion during the lift, which allows faster speeds to be developed.
Secondly, the shape of the hexagonal barbell allows the center of mass of the barbell to travel more vertically, and less horizontally. Indeed, research has shown that when using the hex bar, the horizontal displacement of the barbell away from the body is 75% less than with a straight barbell.
These features may help the hex bar deadlift develop lower body power more effectively than the straight bar deadlift.
What is the takeaway?
Although they are both deadlift variations, the hex bar and straight bar deadlifts differ from one another in several important ways.
The hex bar may allow a heavier load to be lifted, because the external moment arm lengths at the hip, knee, and ankle are all shorter than with a straight bar. This means that more weight can be used for the same lower body and trunk net joint moments. But, it may also require the upper body to play a greater supporting role for a similar lower body training effect, which could be a disadvantage in some cases.
In comparison with the straight bar, the hex bar involves smaller hip and spine net joint moments, but greater knee net joint moments, as well as less hamstrings and erector spinae muscle activation and more quadriceps muscle activation. This makes the hex bar deadlift more quad-dominant, which is why some people regard it as being a hybrid between a deadlift and a squat. So if you are replacing the straight bar deadlift with the hex bar variation, you might want some extra hamstrings work, such as with the Nordic curl.
Finally, the hex-bar involves marginally greater forces, but a substantially faster bar speed, and therefore greater power outputs than the straight bar deadlift. This may arise from a combination of factors, including a larger knee range of motion, and a more vertical bar path, and may make the hex bar more suitable for athletes, who often require high-velocity strength.