The Bio-mechanics of Throwing

 In Upper Limb

Physio Kunal Bhatt discusses with us the bio-mechanics of throwing and the movements involved.

Throwing is a whole body activity that commences with drive from the large leg muscles and rotation of the hips, and progresses through segmental rotation of trunk and shoulder girdle. It continues with a “Whip-like” transfer of momentum through elbow extension and through the small muscles of the forearm and hand.

Throwing movements are often classified as overarm, side arm or under arm but here we are going to concentrate more on overarm throwing. OverArm throwing motion is often regarded as one of the basic motion along with walking, running and jumping.  In sports, throwing is to the upper limb what gait is to the lower limb.

Throwing movements are often classified as overarm, side arm or under arm. #performbetter @pogophysio Click To Tweet

What is Over-Arm Throwing?

Overarm throws are characterised by external rotation of the humerus in preparation phase and its internal rotation in action phase. This movement is one of the fastest joint rotations in the human body.

It is an activity seen in many sports in some form, and there are similarities between all types of throw and with shots in racquet sports.

Overhand throwing does not necessarily means the position of the throwing arm for e.g. in cricket bowling the arm is swung through an overhead position but this motion is not called “overhand throwing” while in baseball there are pitchers with “overhand”,  “three-quarter”, “side-hand” and “under hand” styles. they look initially different to each other but with the close attention to the angles of upper limb joint motion, all are similar with differences in their trunk angles.

The bowler’s in cricket and pitcher’s in softball has strict regulations for actions. However, fielders who have no restriction on their motion prefer to throw a ball with an overhand motion because we can throw faster and more accurately with overhand throwing.

Importance of Bio-mechanics

To understand how to manage the different pathology that arises in the shoulder of the overhead athlete, it is first imperative to understand the biomechanical forces that act on the athlete׳s shoulder with varying shoulder motions.

We will take baseball pitcher as an example because it is a classic example of the shoulder forces experienced by an athlete that performs an overhead throw. It also serves as a basis for understanding shoulder biomechanics in these players. Cricketers, javelin throwers, swimmers, and other athletes also experience similar significant forces about the shoulder.

Phases of Throwing:

  • Preparation / Wind Up
  • Cocking
  • Acceleration
  • Deceleration/follow through

(1) Preparation/wind up: Wind-up establishes the rhythm of the pitch/throw.

During wind-up the body rotates so that the hip and shoulders are perpendicular to the target. During wind up phase the major forces arise in the lower half of the body and muscles of the shoulder are relatively inactive.

  • Minimal force on shoulder during wind-up phase, rotator cuff muscles are inactive during this first phase.

(2) Cocking: The Cocking movement positions the body to enable all body segments to contribute to ball propulsion. It can be further divided into two sub-phases:

  • early cocking phase
  • late cocking phase

The wind up and cocking phase together constitutes 80% of the duration (approx 1500 milliseconds).

Early cocking Phase:

In the early cocking phase, the arm is placed into the abducted, externally rotated position. In addition, the arm rotates behind the body axis about 15 degrees. This phase ends at the “top” of the motion just before the beginning of forward arm and body motion. Early in this phase, the deltoid is active as it abducts the arm, followed by activity in the rotator cuff musculature to cock the arm into a more externally rotated position.

With the maximal external rotation, the shoulder is “loaded”, with the anterior capsule coiled tightly in the apprehension position, storing elastic energy. The internal rotators are stretched. At this stage, anterior joint forces are maximal and can exceed 350 N.

Late cocking Phase:

The late cocking phase begins as the lead leg contacts the ground and ends when the arm reaches maximal external rotation of nearly 180 degrees. During this phase, the scapula retracts in order to provide a stable glenoid surface for the humeral head to compress against. The upper arm is maintained in 90 to 100 degrees of abduction, and the elbow moves even with the plane of the torso. As the humerus progresses into external rotation, the humeral head translates posteriorly on the glenoid owing to increasing tightness in the anterior structures. The external rotators (infraspinatus and teres minor) are active early in this phase, as are the supraspinatus and deltoid. The subscapularis is active toward the end of this phase as the internal rotation of the arm begins. During this phase, the rotator cuff musculature generates a compression force of 650 N.

(3) Acceleration:

The Acceleration phase is extremely explosive. It consist of the rapid release of two forces – the stored elastic force of the tightly bound fibrous tissue of the capsule, and forceful internal rotation from the internal rotators (subscapularis, pectorals major, latissimus dorsi, teres major) . This generates excessive forces at the glenohumeral articulation and thus the cuff musculature remains highly active to keep the humeral head relocated in the glenoid.

The acceleration phase concludes with ball release, which occurs at approximately ear level.

Acceleration phase lasts approximately 50 milliseconds which is 2% of overall time.

(4) Deceleration/follow through:

In the deceleration/ follow through phase very high forces pull forward on the glenohumeral joint following ball release, which places large stresses on posterior shoulder structures. The arm continues to extend at the elbow and internally rotate at the shoulder. The rotator cuff (external rotators) decelerates the rapid internal rotation of the shoulder, as does eccentric contraction of the scapular stabilizers and posterior deltoid fibres.

The trunk is flexed eccentrically and the lead leg is extended pushing into the ground eccentrically to absorb energy.

This phase places large stresses on the elbow flexors as well as the posterior shoulder structures. This phase lasts approximately 350 milliseconds and constitutes approximately 18% of the total time.

Kunal Bhatt

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