I think we can all agree lifting heavy things is awesome. Unlike other big lifts, deadlifts require minimal mobility in order to be successful. Your ankles don't flex much, your knees stay at or above 90, and your back stays relatively straight. However, your hips are near full flexion at the bottom of the movement.
Being a hip dominant exercise, most of the stress of the deadlift should be in your hip muscles. Your hips are made up of your pelvis and femur, therefore, whatever connects them should be your "prime movers."
If we look one joint away from your hips (your back and your knee) we have your "stabilizers." What connects your pelvis to your back and femurs to your tibias are considered stabilizers because they do not "lift" the weight, instead they maintain a position of your body as the prime movers do the heavy lifting. In other words, your back keeps your spine straight while your hamstrings pull you upright.
People will often jump up in arms and say that deadlifts are a back exercise. They'll say by moving from a flexed forward position to an upright position, your back has to be a prime mover. That is not correct. When you begin a movement in a back extended position (such as the deadlift), it is not the job of the back extensors to move weight. It is the job of the back extensors to maintain extension while the weight tries to produce back flexion. More back extension should not be your primary strategy for making yourself upright during the deadlift. Extending a flexed joint, such as the hips during a deadlift, is the prime motion. Therefore hip extensors are prime movers.
"Back extension should not be your primary strategy for making yourself upright during the deadlift"
Your quadriceps, hamstrings and glutes are the prime movers for the deadlift. In the initial pull, where your hips are maximally flexed and your knees are bent between 85-45 degrees, your hamstrings stabilize your shin while your quads extend your knees. This phase is often characteristic of a strong, whole-leg contraction and some serious leg shaking. As you clear your knees and enter the second pull, your hamstrings begin to take on a greater hip extension role to bring you back to upright. Finally, the last few degrees of hip extension are driven by your glutes to help you achieve a fully upright stance.
If you want to get rid of your back pain after deadlifting, first you need to check your technique. There are plenty of youtube videos to take a look at for deadlift technique. If you want someone to review your technique, send me a video at this email and I'll do so for free (firstname.lastname@example.org). For those who feel their technique is pretty solid but they cannot keep their back from dominating the movement or they never feel their backside legs working, we need to dive deeper into the hips.
Are you aware that your hips internally rotate when you bend forward?
Here's what I mean.
In this picture we have hip internal rotation as measured in the seated position. Typically we want 45 degrees of this motion. In regards to deadlift performance we want more than 40 degrees of internal rotation at the hip because as the pelvis flexes over the top of the femur (aka rotates forward like when you bend down to touch your toes) the femur moves backward into the socket. That's right, as your pelvis rotates forward over the top of your legs, the top of your leg bone slides back into the socket. If you can't picture this motion, watch this video. Essentially, if you sit on a high surface and cannot do with your leg what the guy above is doing, you cannot control your femur in your socket. You can't control your femur in your socket because your active motion is less than your passive motion (strength problem) OR your socket doesn't even allow for the motion to occur (mobility problem).
First, establish full hip extension on both legs, then each leg individually. If the issue is predominant on one side you do not want all of your interventions to be symmetrical bilateral stance or you will compensate right through and nothing will change.
First train your hips how to properly sit on top of your legs. If you don't start from a fully upright position, you won't be able to flex forward all the way into a fully flexed position.
Second, ensure you have appropriate abdominal capacity to pull the ribs down and back (if your ribs are flared then your pelvis will anteriorly tilt and your posterior capsule musculature will tighten, closing the posterior capsule down).
Your core needs to work if you want to be able to rotate through your hips. To deadlift properly your rib cage and pelvis should be stacked. Your back shouldn't be hyperextended, opening the front of your belly and your back shouldn't be rounded out either.
Third, clear out restrictions from the calves and low back, as these will also hold the pelvis in a position that limits internal rotation and forward flexion.
Fourth, train internal rotation. This means adductors and anterior gluteus medius muscles. These are often ignored and rarely touched on in a typical training program. Maybe that's why you're hurt!
Fifth, deadlift correctly.
To clarify, your back SHOULD NOT hurt after deadlifting. It may hurt because you're lacking any of the concepts above. If you want to know what you're missing, get evaluated by a competent Performance Physical Therapist like the team at Human Function and Performance.
Questions? Email them to email@example.com or visit our website humanfunctionandperformance.com for free resources, access to exclusive workshops, and the rest of the blog that puts together how a human body should operate.