The trap bar deadlift and the regular Olympic bar version may look identical to the untrained eye but they’re not.
When using the trap bar for deadlifting you are performing a combination of a squat and a deadlift. When you are in the ‘trap’ you are still pulling the weight, but you have the luxury to have your back much straighter and in consequence your legs are more involved in the movement. On the other hand when you do regular straight bar deadlifts your starting position and groove is different because the bar is always in front of you no matter what.
Trap bar deadlifts allow you to sort of squat your deadlift. You can get away with having your hips a little lower. In contrast the regular deadlift requires you to have your hips higher since otherwise you will be in an inefficient pulling position.
If you try a regular deadlift with your hips low, you will be weaker and the movement will feel weird.
What about the targeted muscles?
The trap deadlift works your quadriceps a little more than the regular deadlift which could be a good thing, if you can’t squat. At the same time the Olympic bar deadlift targets the back musculature and the posterior chain (glutes + hamstrings) more. All of that is due to the different bio-mechanics of the lifts.
Which is better?
None. When it comes to exercise selection you should always evaluate the situation prior to labeling an exercise as good or bad. If you perform a regular deadlift, you get more back development. But what if your back is troublesome and you feel better doing trap bar?
You could also combine the two versions and alternate. You may do trap bar deadlifts as accessory movement to the deadlift.
An additional bonus of doing trap bar deadlifts is that there’s no contact between your lower leg and the bar which means less shin bleeding.
Interesting fact: One of the best deadlifters ever, Bob Peoples (above image), used the trap bar deadlift as a supplementary lift.
Related article: Does Olympic Weightlifting Really Build Muscle?
Which is easier on the lower back?
It’s hard to tell and depends on the individual. Some say the trap bar is the better since you are more upright. However, there’s no contact between you and the bar at the top of the movement and your lower back will have to work harder to stabilize the weight. For some this is not an issue but you never know.