Biomechanical terms

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Bio-mechanical terms

This wiki segment is derived from the article "Defining the game through biomechanics" by Joe Slowinski December 2011

Joe's website is

References White, N. (2003). Measurement of Joint Motion: A Guide to Goniometry (4th edition) Philadelphia: F.A. Davis Company.

Forearm Supination/Pronation

The neutral position for the forearm is the thumbs up position. When the hand and forearm face the ceiling, the forearm is rotated to approximately 90 degrees of supination. Conversely, when the forearm faces down, it is in approximately 90 degrees of pronation. According to both the American Medical Association (AMA) and the American Academy of Orthopaedic Surgeons (AAOS), the normal range of motion (ROM) for both forearm supination and pronation is 80 degrees.

Wrist Flexion/Extension

The neutral (0 degree) position of the wrist is the fingers straight and the hand aligned with the forearm. Flexion at the wrist involves movement of the palm of the hand toward the palm side of the forearm. In colloquial bowling speak, this has historically been referred to as cupping the ball. Wrist extension is moving the fingers and palm away from the palm side of the forearm. Extension is often referred to as breaking the wrist. The normal ROM for wrist flexion is 60 degrees (AMA) to 70 degrees (AAOS). According to the AMA, the normal ROM for extension is 60 degrees whereas the AAOS reports it as 70 degrees.

Wrist Ulnar Deviation/Radial Deviation

Ulnar deviation is moving the wrist medially, toward the body. It is named for the ulna bone, a long bone on the inside (when the forearm is supinated) of the forearm. This is also known informally in bowling circles as cocking. Both the AMA and the AAOS rate the normal ROM for ulnar deviation as 30 degrees. Radial deviation moves the wrist laterally, away from the body. The radius bone is located on the thumb side of the forearm and is also a long bone in the forearm. The normal ROM according to both the AMA and the AAOS is 20 degrees.

Elbow Flexion/Extension

Elbow flexion is moving the forearm toward the upper arm and body. Extension refers to the movement away from the upper arm and body. In the set up of most bowlers, the forearm is supinated and flexed at ninety degrees or higher of elbow flexion. The AAOS states that the normal ROM is 150 degrees with 140 for the AMA. The neutral or zero position is the arm fully extended.

Trunk Lateral Flexion

Lateral flexion is leaning or bending the trunk to the side. For bowling, in the modern game, in order to establish an improved line of sight and space for the swing slot, lateral flexion is a critical element of an efficient game. The neutral or zero position would be standing straight. The normal ROM for the lower (lumbar) and middle (thoracic) spine is 30 to 35 degrees. In the October 2010 Slowinski at-large, I discussed the body position in which trunk lateral flexion helps create space for the swing slot as well as enhancing torso rotation.

Shoulder Extension/Flexion

In bowling terms, shoulder flexion (forward) and extension (backswing) are an important component of the physical game. The neutral position of shoulder extension or flexion is at the side, adjacent to the leg. With the arm in front of the body, the shoulder is flexed slightly. Flexion is forward movement with a normal ROM of 150 (AMA) or 180 (AAOS). The normal ROM of extension is 50 (AMA) or 60 (AAOS) degrees. Pay special attention to the normal ROM in regard to shoulder extension. The height of the swing can only be achieved by trunk flexion.

Shoulder Adduction/Abduction

Abduction is to move the upper arm away from the body. Adduction is to move the upper arm toward your body.

Trunk Flexion

The normal ROM for the lower (lumbar) and middle (thoracic) spine is 80 (AAOS) and 60 (AMA) degrees.

Trunk Rotation Some bowlers rotate the torso which places the ball-side hip and shoulder behind the balance arm side hip and shoulder.

Knee Flexion

Bending at the knee is knee flexion. The normal ROM is 135 (AMA) or 150 (AAOS).