So in my last post, I explained how training too heavy can impact range of motion (ROM) and rep ranges. Basically, if you can't do more than one rep, or you can do 6 reps but they're all partials--you are training way too heavy! But training too heavy also impacts form, and form is possibly even more important to pay attention to, especially in those areas where people are tempted by setting personal records for themselves, i.e. Olympic lifts such as deadlifts, cleans, etc. Ever wonder why you never see people doing PR's on biceps curls? You're probably thinking "It would be pointless to do that on biceps curls." Well, it's just as pointless to do it with any other exercise also--the logic is the same in either case. Deadlifts are a great strengthener for hips, lower back, core, and legs--but they must be performed for reps and they must be performed perfectly!
Deadlifts are an exercise that can make or break your workout. Some people like to include them on leg day, some do them in a workout all by themselves, but most of us use them for augmenting our back training. Because of the intense amount of strain being placed on the lower back, it is crucial that your back stay straight and flat, and that you do not use your lower lumbar region as a lever--conventional deadlifts do not involve rotation at the hip, a la Romanian deadlifts, good mornings, or hip hyperextensions. Unlike most other muscles in the body, the spinal erectors are not designed for flexion or extension--they are only designed to hold a static, stabilizing position. No matter how strong and thick your lower back gets, this will not change.
To set up properly for conventional deadlifts, assume a neutral stance with feet at a comfortable width (this will vary by individual but generally shoulder width is a good place to start). Your hands should be set up on the bar just outside your legs--I do not recommend using a staggered grip, i.e. one hand over, one hand under. There are a lot of powerlifters out there with one detached biceps tendon or forearm extensor from using this method--I know some of them personally. Just like you would never perform bent-over rows with a staggered grip, you do not want to be stressing each side differently during deadlifts either. Additionally, the wider your grip, the farther you must travel in order to rest the weight on the floor, so don't set up too wide.
Now you want to squat down so that your shoulders are the highest point--drop your hips completely! This is not something that can be varied, your hips must stay low for safety and functionality! Allowing the hips to come up first changes the movement significantly, resulting in dangerous lower back strain and forcing the quadriceps and hamstrings to do all the work--not the intention of conventional deads! Once properly set, you should pretty much look like you are in the bottom of a deep squat.
From this squatting position, you want to explode upwards through the shoulders, keeping the chest up and hips down. Keep the pressure generally in the middle of your feet--rolling onto the toes changes the movement as well and further tempts your hips into coming up first. As your legs extend and move out of the way, you should be able to further straighten your upper back and rotate the shoulders back even more, resulting in a nearly completely upright stance. It is absolutely essential that your hips stay low during the concentric and eccentric phases--I simply cannot stress this enough. Return the weight to the floor using the same path--lowering the weight ultra-slowly is not recommended, neither is tossing the weight back to the floor--I believe a controlled drop somewhere in the middle is ideal for strength, safety, and adaptive response. Each repetition should be thought of, and performed, as if it were a separate, distinct movement. Ideally you want to allow the bar to come to rest before lifting again--it's called a deadlift for a reason.
See how on some of my reps with 225, my hips come up a tiny bit first, rather than staying low as I drive through the shoulders? Even though it's pretty minor, and I successfully completed six reps, the form breaking down on my last set necessarily limits my progression--that is, I would never consider trying for 275 until I could do that same set, but perfectly. Now, I could probably throw 315 on there and eke out one single rep--but why? I would gain no strength adaptations from a set like that, and bragging rights are pointless when 1) people already know you're strong and 2) you don't care what people think anyways.