The deadlift from a biomechanical point of view

Keep the bar close to your body is a frequently mentioned deadlift tip. In this week’s post, you will find out if there lies any truth in this statement. I will analyze the deadlift for you from a biomechanical point of view. By the end of this post, you will be able to better understand the rationale behind this tip.

Important background information 

The human body has to deal with different forces while performing the deadlift. First of all, you will have to overcome the forces created by the barbell. Then, there is also the downward force created by the HAT: head, arms, and trunk. You will have to contract your lower back (erector spinae), glutes en hamstrings to prevent falling over and thus match/overcome these two forces. The focus in this post will be on the lower back musculature.

Biomechanical analysis 

Keeping the barbell close to your body in a deadlift is a simple way to lift more weight. This can be explained by a changing moment as a result of a differing lifting technique. A moment is a turning effect produced by a force. 

Imagine a seesaw with 10kg on the right side and 5 kg on the left. If the distance of the weight to the pivoting point is on both sides the same, the 5kg will be lifted off the ground. The closer the 10kg is moved to the pivot point, the slower the 5kg will rise. At some point, the seesaw will be completely balanced. In such a situation, the turning effect, which is the product of the weight and moment arm, is the same on both sides.

As you can see, the moment M depends on the force and moment arm, where the moment arm is the shortest distance between the pivoting point and the line of force acting on that pivot point. This results in the following formula: M = F (force) * r (length of moment arm). Two conclusions can be drawn from this formula:

  1. The greater the force, the greater the turning effect (a.k.a. the moment).
  2. The greater the moment arm, the greater the turning effect.

When you perform a deadlift, the same principles apply as described in the previous example. The joint axis (pivot point) is located in the spine (between vertebrae lumbale 5 en sacrum 1). As illustrated in the image, the forces of the barbell, head, arms and trunk work on one side of the joint. The lower back muscles will apply force on the other side of the joint axis. The moment arm of the lower back muscles is fixed and surmounts to approximately 6 cm 1. However, the moment arm of the barbell and HAT can be tweaked by adjusting your technique and posture.

To get a stronger deadlift you should keep the bar as close to your body as possible. The moment created by the barbell will decrease as a result of this small but critical tweak. The lower back muscles, which are located on the other side of the joint axis, will have to produce a smaller moment as a direct result of this change in technique. As the moment arm of the lower back muscles is fixed, the erector spinae is ‘allowed’ to produce less force compared to a situation where the moment arm of the barbell is greater. In essence, you will be able to lift the same weight with less effort.

More specifically, by keeping the bar close to your body, you can lift more weight (while the moment is still the same). However, the lower back will have to produce the same amount of force in both situations, meaning that the mechanical stress on the muscle is the same in both situations. A muscle only recognizes the mechanical stress(which is the same) and doesn’t see how many plates you are lifting. The question then remains: why you would like to add more weight to the barbell? My answer to this is twofold:

  1. Consistency: keeping the bar close to your body will result in consistent execution of the exercise. Your body functions as a benchmark. This will help you to perform very similar reps. This is especially important if you want to apply progressive overload to your muscles. The benchmark helps you to perform every rep roughly the same. This will help you better determine your total workload which you can then slowly increase every workout.
  2. Powerlifting: lifting as much weight is a goal in itself in powerlifting. Keeping the bar close to your body will help powerlifters achieve this goal. 

So from now on, focus on keeping the bar as close to your body as possible. It will help you to perform reps more consistently as well as lift more weight in total (which is a nice benefit for the ego-lifters between us :)). Please share this article if you learned something and enjoyed reading it!

 

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