Concentric vs Eccentric
As a result of the different starting positions, each exercise works the muscles through different lift phases. These phases are called concentric and eccentric.
In simple terms, the concentric phase is the lifting portion of the exercise. While eccentric is the lowering portion, also called the negative.
Since the deadlift starts from the floor, the focus is the concentric phase or lifting the weight. Followed by a controlled drop to the floor.
By comparison, the Romanian deadlift starts with a controlled eccentric phase or lowering the weight. And the concentric phase follows to raise back to the starting point.
Range of Motion
As I mentioned earlier, another significant difference between the Romanian deadlift vs deadlift is the range of motion.
The conventional deadlift works your body through the entire range of motion, from squatting to standing.
On the other hand, the Romanian deadlift focuses on the top half of the range of motion from bent over to standing.
Last, but perhaps most important, is the difference in mechanics between the two deadlift variations. In other words, how your body moves during the exercise.
With the standard deadlift, you bend at both the knees and hips. But you bend mainly at the hips with the Romanian deadlift.