Related Experiment Video

Updated: Apr 5, 2026

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

Published on: March 12, 2021

Configuration of the Shoulder Complex During the Arm-Cocking Phase in Baseball Pitching

Shoji Konda¹, Toshimasa Yanai², Shinji Sakurai³

¹Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan skonda@caos.med.osaka-u.ac.jp.

The American Journal of Sports Medicine

|August 13, 2015

Abstract

Background:

The role of the scapula during high-velocity baseball pitching has been described without 3-dimensional kinematic data. It has been speculated that the scapula functions to align the humerus with the spine of the scapula on both the transverse and scapular planes at the end of the arm-cocking phase.

Hypothesis:

Two hypotheses were formulated: (1) the scapulothoracic protraction angle correlates with the humerothoracic horizontal adduction angle among participants, and (2) the scapulohumeral rhythm of the humerothoracic elevation is not the same as the normal ratio (2:1) observed widely in controlled abductions.

Study Design:

Descriptive laboratory study.

Methods:

A total of 20 Japanese professional baseball pitchers were asked to pitch 3 fastballs as they would normally during pitching practice. The 3-dimensional kinematic data of the thorax, scapulae, humeri, and pelvis were recorded using an electromagnetic tracking device operating at 240 Hz. Humerothoracic, scapulothoracic, and glenohumeral joint configurations were determined at the instant of stride-foot contact (SFC) and the end of the arm-cocking phase (MER).

Results:

The mean (±SD) glenohumeral horizontal adduction (-6° ± 7°) and elevation (85° ± 10°) angles at the MER indicated that the humerus was positioned almost parallel to the spine of the scapula. The mean scapulothoracic protraction angle (15° ± 10°) was significantly correlated with the humerothoracic horizontal adduction angle (10° ± 11°) at the MER (r = 0.76, P < .001) but not at the SFC (r = 0.13, P = .58). The scapulohumeral rhythm (4.2 [±1.9]:1) expressed as the ratio of the glenohumeral elevation angle to the scapulothoracic upward rotation angle at the MER was significantly greater than the normal ratio (2:1) (P < .01).

Conclusion:

The results supported the hypotheses, providing evidence to corroborate the widely accepted concept that the scapula functions to align the humerus with the spine of the scapula so as to limit the glenohumeral joint configuration within the "safe zone" at the MER.

Clinical Relevance:

Disruption of coordination, such as abnormal patterns including "SICK" scapula (scapular malposition, inferior medial border prominence, coracoid pain, and dyskinesis) and scapular dyskinesis, may result in an abnormal configuration of the glenohumeral joint at the MER.

Keywords:

biomechanics glenohumeral joint kinematics scapula scapular plane

More Related Videos

Reverse Total Shoulder Arthroplasty

Reverse Total Shoulder Arthroplasty

Published on: July 5, 2011

Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact

Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact

Published on: February 10, 2015

Related Concept Videos

Muscles of the Shoulder

Muscles of the Shoulder

The muscles surrounding the shoulder girdle, including the clavicle and scapula, primarily stabilize the scapula. This stable base allows other muscles to move the humerus effectively. Scapular movements often mirror those of the humerus and extend its range of motion. For instance, raising the arm above the head would not be feasible without simultaneous upward rotation of the scapula.
Anterior Thoracic Muscles
The anterior thoracic muscles include the serratus anterior, subclavius, and...

Bones of the Upper Limb: Humerus

Bones of the Upper Limb: Humerus

The upper limb consists of the arm, forearm, wrist, and hand bones. The humerus is the single bone of the upper arm region. Proximally, it has a large, spherical, smooth head that articulates with the glenoid cavity of the scapula to form the glenohumeral or shoulder joint. The margin of the head is the anatomical neck, a residual epiphyseal plate. Laterally it extends to form bony projections called the greater tubercle and the lesser tubercle. Next to the tubercles is the surgical neck, a...

Muscles that Move the Arm

Muscles that Move the Arm

Nine muscles are involved in arm movements. Two of these, the pectoralis major and latissimus dorsi, originate from the axial skeleton and are called axial muscles. The other seven originate from the scapula and are called the scapular muscles.
The pectoralis major has two origins. Its clavicular head originates on the medial half of the clavicle. In contrast, the sternocostal head originates on the costal cartilages of ribs 1-6, the sternum, and the aponeurosis of the external oblique of the...

Muscle Coordination and Action

Muscle Coordination and Action

Muscle coordination is a complex and finely tuned process essential for smooth and purposeful movements like flexion, extension, adduction, abduction, and rotation. The human body orchestrates the actions of various muscles working in concert, each with a specific role. Four functional types describe how muscles work together: agonist, antagonist, synergist, and fixator.
Agonists
Agonist muscles, often called prime movers, are the primary muscles responsible for producing a specific movement....

Muscles that Move the Forearm

Muscles that Move the Forearm

The muscles that move the forearms can be divided into four groups: forearm flexors, forearm extensors, forearm pronators, and forearm supinators. The flexors and extensors act on the elbow joint, while the pronators and supinators act on the radioulnar joints.
Forearm Flexors
The biceps brachii, brachialis, and brachioradialis are forearm flexors. The biceps brachii is made up of two heads. Its long head originates at the supraglenoid tubercle of the scapula, whereas that of the short head is...

Bones of the Upper Limb: Radius

Bones of the Upper Limb: Radius

The radius is longer of the two bones that make up the human antebrachium or forearm. At the proximal end, the radius articulates with the capitulum of the humerus and the radial notch of the ulna to form the elbow joint. At the distal end, the radius articulates with the ulna via the ulnar notch, forming the distal radioulnar joint. Distally, the radius also attaches to the carpal wrist bones (scaphoid and lunate) to form the radiocarpal joint.
The radius has a nail-shaped head, and a...

Articles linked to this work by shared authors, journal, and citation graph.

Biomechanical comparison between toe and edge jumps in figure skating: focusing on toe-loop and loop in female skaters.

Sports biomechanics·2026

A pragmatic single-group evaluation of a self-determination theory-informed health literacy course for exercise behavior readiness among Japanese university students.

Frontiers in sports and active living·2026

Dynamic balance status and ankle mobility in adolescent basketball players with a history of multiple lateral ankle sprains.

Clinical biomechanics (Bristol, Avon)·2026

Biomechanical insights into increasing jump distance in ski jumping: a review classified by hill size.

Frontiers in sports and active living·2026

Weakening of the Active Muscle Restraint Against Valgus Loading During Repeated Baseball Pitching: Direct Evidence of Fatigue in Dynamic Valgus Stabilizers of the Elbow Joint in Collegiate Baseball Pitchers.

The American journal of sports medicine·2026

The extrapolated body center of mass predicts subsequent foot placement choice during dynamic single-leg landings.

Journal of biomechanics·2026

See all related articles