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Thoracic Outlet Syndrome in Throwers

TOS in overhead athletes

When boiled down to its core, rotational movements of throwing, striking, and even change of direction are very similar. Biomechanically, there is a transfer of force from one side of the body to the other. The phases of throwing are the wind-up to cocking phase, the drive phase, and the follow through. Each of these phases involve opposite motions on each side of the body.

Problems can arise through an area of the body called the thoracic outlet when muscles around the neck and upper ribcage get tight and compress on nerves or blood vessels. Thoracic Outlet Syndrome can cause numbness and tingling down the affected arm, weakness of the arm and hand, or at its very worst, blood clots.

When an overhead athlete has tingling in their throwing arm, Thoracic Outlet Syndrome always has to be considered as a cause and must be looked at because of its prevalence in these athletes.

Biomechanics of Throwing 101

During the cocking phase, the non-throwing side is compressed while the throwing side is more expansive. In a right-handed athlete, this involves the right arm going into external rotation (ER), flexion, and abduction while the left arm does the opposite. For right handed, throwers, opening up the right side of the chest to do this movement is difficult because of soft tissue limitations through the right chest wall and rotation of the trunk.

During the drive phase, the non-throwing arm will begin to supinate, ER, and flex while the throwing arm pronates, IRs, and extends. This creates a torque through the ribcage, shoulder, and hand, compressing throwing side of the body maximally at the release point of the ball.

When right handed throwers follow-through, their left hip has to internally rotate in order to accept their weight and decelerate their right arm. This process is required to produce maximal power in any rotational movement. Baseball pitching, volleyball hitting, throwing a straight in boxing, and getting around an offensive lineman all require a powerful rotation that involves transferring power from trail leg to the trail arm, then decelerating the body with the lead leg and arm.

TOS Overview and Throwing

Thoracic Outlet Syndrome is characterized of compression of nerves and blood vessels that pass through the space between the first rib and collarbone. Fascial restriction and compression can happen because of muscular tension through the front of the neck with overworked scalene and subclavius muscles.

Normal human asymmetry leads to a stiffening of the right upper chest and ribcage area with poor ability to expand the lung here. If we look at the cocking phase of overhead movement, we can see that the upper chest must open in order for the right hand to go behind the head and prepare for the movement. When the right chest can’t open, the muscles of the right neck will turn on in order to aid in the rotation of these ribs and preparation for movement. This can lead to elevation of the first rib and will close down the space of the thoracic outlet.

Relationship of Upper Rib Elevation and the Serratus Anterior

Due to the scalenes attachments on the ribcage, these muscles will elevate the first 3-4 ribs and start to rotate the spine toward that direction. When this occurs on the right side as it often does, this is known as Superior T4 syndrome (PRI) and is a form of pathological or compensatory airflow. The serratus anterior muscle is a huge player in it’s role shoulder stability due the attachment on the inside of the shoulderblade; however, what’s often overlooked is its attachment on the ribcage.

If we look at the pull of the fibers, it will depress the first four ribs and elevate the lower four. This is the exact opposite of the orientation of the ribs in superior T4 airflow, therefore, we can conclude that if the neck muscles are pulling the upper four ribs into elevation and the lower ribs are still in a depressed state, then the serratus anterior muscle will be in a lengthened state in which it cannot fire in an optimal manner from the attachments on the ribcage. Due to the attachments on the shoulder blade, a lengthened serratus anterior would lead to scapular winging and poor protraction (shoulder going forward) and upward rotation.

Relationship of the Serratus Anterior and Weight Acceptance

The follow through phase of the movement involves weight acceptance of the left leg. The main muscles required for this are the left glute med and adductor working together to create an opening of the back of the left pelvis and closing down of the left ribs. These movements cause a deceleration of the throwing arm through its connection to the stance leg.

Let’s assume that in a right handed thrower (or attacker or boxer), they have upper rib elevation (superior T4 syndrome) with an overactive neck and underactive serratus anterior on the right side. If the right serratus anterior is lengthened, then from a neurological perspective, the upper body is unable to decelerate properly. Therefore, we can assume that without proper right serratus anterior function, the body will have to find a way to accept its weight (or decelerate) without using the adductor or glue med. This can lead to excessive stress placed on the lead leg, lower back, or throwing arm.


Thoracic Outlet Syndrome is a common diagnosis in overhead athletes because of the demand of ribcage rotation, chest wall flexibility, and high amounts of force involved in rotational movements in sport. When the body cannot optimally produce and then decelerate these forces, compensation occurs, and it often happens in the area of the thoracic outlet. Accurate assessment of all three phases is a must when working with any overhead athletes.

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