The Effect of Arm Angle in the Supine Grip in the Deadlift

by Mia Inman, PhD, SSC | December 05, 2023

Efficient pulling mechanics in the deadlift are constrained by three factors: 1) the bar must be placed directly over the mid-foot, and maintain that position during the lift, 2) the body-barbell system must be in balance over the mid-foot, and 3) the efficiency with which the lats pull back on the humerus. These three factors dictate the standard pulling position in the setup of the deadlift, in which the hips are high, the shins are against the bar, and the shoulders are slightly ahead of the bar. This forward shoulder position results in a ~7-10 degree deviation in the angle of the arm segment from a vertical, or plumb, line.

At this slight angle, the forces along the arm segment are mostly tension. However, some moment down the arm exists, caused by gravity that tries to pull the bar forward and the arm into a vertical alignment. The bar must be held against the legs during the pull to prevent the bar from swinging forward, which would introduce an unnecessary moment arm between the bar and the mid-foot and prevent a sufficiently heavy deadlift from being pulled from the floor.

You might think to pull your shoulders back, so that they are directly over the bar, with no moment around the shoulder joint. However, with almost all of your body mass behind the bar, you would be out of balance, with your weight on your heels. You may counter this by dropping the hips, but this would push your shins forward, and the bar forward of the mid-foot, violating the criteria for an efficient deadlift. Thankfully, your body knows mechanics far better than you do, and will automatically shift your hips back up and your shoulders forward, to put you in an optimum position to pull a heavy weight from the floor.

So, we are stuck with this "shoulders ahead of the bar" position for efficient pulling mechanics, and the resultant gravitational moment force around the shoulder joint and down the arms. To keep the bar against the legs, and maintain efficient pulling mechanics, we use the lats to provide a counterforce to the moment around the shoulder. The lats, which distally insert on the intertubercular (bicipital) groove near the head of the humerus, pull back on the arm (the wrench) very close to the shoulder joint (the bolt), whereas gravity acting on the bar is pulling at the far end of the arm (the wrench). The lats are, therefore, at a significant mechanical disadvantage. The lats need to be very strong and pull at a very efficient angle of attack on the humerus, in order to win the battle for control of the arm segment, and keep the bar against the legs and over the mid-foot.

There is an internal moment arm between the head of the humerus in the glenoid fossa and the distal insertion of the lats, which multiples the contractile force of the lats. Critically, in the standard pulling position described above, when using a double-overhand grip, the lats pull on the humerus at ~90 degrees. This angle of attack maximizes the internal moment arm, and consequently the counterforce provided by the lats, enabling the position of the bar to be maintained against the legs.

This is all well and good, but difficulties may arise when the weight gets sufficiently heavy that you have trouble holding onto the bar with a double-overhand grip. You may instead choose to use an alternate grip, where one hand is supinated while the other is prone. As has been discussed in another article, the bar on the supine side can drift forward away from the shins as the bar comes off the floor due to a number of factors, one of which is the change in arm angle due to the position of the hand behind the bar.

When you move your hand from a prone position (palm on the front side of the bar) to a supine position (palm on the back side of the bar), this changes the angle of the arm. As can been seen in Figure 1, when Elliot moved his hand from a prone to a supine grip, this changed his arm angle by ~3 degrees.  

This seemingly subtle shift to a more horizontal arm angle has two implications with regard to your ability to maintain the bar against your shins on the supine side.

The first is that the more horizontal arm angle decreases the angle of attack of the lats on the humerus. This reduces the internal moment arm between the distal insertion of the lats and the shoulder joint, diminishing the pulling efficiency of the lats against the humerus. While this may only be a few degrees of change (this will vary with the thickness of both the bar and the distal end of the palm), the gravitational moment force around the shoulder joint imposed by very heavy weights may be too much for your lats to provide a sufficient counterforce, and the bar may swing forward of your legs on the supine side.

This lack of pulling efficiency from the lats is compounded by the second effect from changing the arm angle. As the arm becomes more horizontal (less vertical), the forces down the arm segment have less tension and more moment. More moment means more rotational force around the shoulder joint, that has to be countered by the (now less efficient) lats.

The external moment arm, which introduces moment at the shoulder joint and down the arm, is presumed to be the horizontal distance between the shoulder joint and the bar. This moment arm should, therefore, be the same for both the prone and the supine grip, since the position of the bar relative to the shoulder joint is the same for both grips.

However, as noted above, due to the more horizontal arm angle on the supine side, there must be more moment around the shoulder joint. Therefore, the moment arm between the shoulder joint and the end of the arm segment on the supine side must have increased. To understand how the moment arm can increase by simply changing the grip, while the relative positions of the shoulder joint and bar remain the same, we have to think about the moment arm(s) between the shoulder and the bar in a slightly different way.

Force is transmitted from the shoulder joint, down the rigid arm, through the palm to the fingers on the underside of the bar. Rather than thinking of this being a single segment, we can consider instead it as two segments. The first is from the shoulder joint to the end of the rigid arm segment where it contacts the bar, at the distal end of the palm. The second is from the distal end of the palm to the proximal phalanges of the fingers underneath the bar, supporting the load (the distal and middle phalanges help to maintain the position of the bar directly over the proximal phalanges).

Therefore, two external moment arms have to be considered when looking at the effect of a supine grip on the ability to keep the bar against the shins:

1. M.A.arm is the external moment arm from the head of the humerus in the glenoid fossa to the distal end of the palm. This moment arm multiplies the gravitational moment force trying to pull the arm to a vertical position. As can be seen Figure 1, there is a significant difference in M.A.arm between the prone and supine grips. At heavy weights, the larger M.A.arm on the supine side will significantly increase the moment at the shoulder, resulting in an increased tendency for the bar to drift forward of the legs and mid-foot.

2. M.A.fingers is the external moment arm from the point of force application of the bar (sitting on the proximal phalanges of the fingers) to the distal end of the palm behind the bar. The fingers are under a combination of moment and tension, and this moment arm multiplies the force of the load on the bar to try and open up the fingers and loosen the grip. If you have a thicker palm and/or use a thicker bar, this moment arm will increase, making it more difficult for you to maintain your grip on the bar.

There are advantages and disadvantages to an alternate grip. You are better able maintain your grip on the bar with an alternate grip because as the bar rotates out and down from the supine fingers it rotates into and up the prone fingers, thus canceling the rotation. But the fact that the palm is behind the bar on the supine side means that some moment force exists on that side of the pull that will have to be countered if the bar is not to drift forward from the supine side. Realizing that this happens and why allows the lifter to plan for the event.