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Modelling and simulation of tissue load in the upper extremities
Published in Youlian Hong, Roger Bartlett, Routledge Handbook of Biomechanics and Human Movement Science, 2008
Fundamental shoulder mechanics: The shoulder allows placement of the hand in a vast range of orientations necessary to perform a spectrum of physical activities. The joint’s intricate morphology, including the gliding scapulothoracic interface, enables this versatility. Table 2.1 contains descriptions of the roles of the principal shoulder components. However, high postural flexibility comes at the cost of intrinsic joint stability, as is widely reported (an overview is provided in Veeger and Van der Helm, 2007). The shallowness of the glenoid fossa requires additional glenohumeral stability generation from one or more mechanisms: active muscle coordination, elastic ligament tension, labrum deformation, joint suction, adhesion/cohesion, articular version, proprioception, or negative internal joint pressure (Schiffern et al., 2002; Cole et al., 2007). Systematic consideration of the impact of these many mechanisms is arguably required in order to replicate physiological shoulder muscle activity. Beyond this concern, the mechanical indeterminacy in the shoulder must be addressed, as there are more actuators (muscles) than there are degrees of freedom (DOF), by most definitions.
Designing for Upper Torso and Arm Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
The other bone of the pectoral girdle, the scapula, is relatively triangular in shape with a prominent ridge, the spine of the scapula, palpable from the body surface (refer to Figure 4.17). Several other features are located at the upper lateral angle of the scapula: the acromion, the coracoid process, and between these two structures, the glenoid fossa. The glenoid fossa is a key structure in the glenohumeral joint, the articulation between the arm and the scapula. The scapula curves to approximate the shape of the rib cage.
Do baseball pitchers improve mechanics after biomechanical evaluations?
Published in Sports Biomechanics, 2018
Glenn S. Fleisig, Alek Z. Diffendaffer, Brett Ivey, Kyle T. Aune
Pitching injuries continue to be prevalent for all levels of baseball (Conte, Camp, & Dines, 2016; Fleisig et al., 2011). While many other sports injuries are caused by traumatic events, almost all baseball pitching injuries are non-contact with chronic pathology (Fleisig, Andrews, Dillman, & Escamilla, 1995; Fleisig, Escamilla, & Andrews, 1996; Fortenbaugh, Fleisig, & Andrews, 2009; Hurd, Kaufman, & Murthy, 2011; Hurd et al., 2012; Werner et al., 2007). Previous studies have shown that variations in mechanics produce increased joint forces and torques and increased rates of injury. Crotin and colleagues demonstrated that changing stride length affected momentum passed up the body and overall exertion, possibly influencing ball velocity and risk of arm injury (Crotin, Kozlowski, Horvath, & Ramsey, 2014; Ramsey & Crotin, 2016; Ramsey, Crotin, & White, 2014). In addition to the distance of stride, the direction of stride is also important. If the front foot landed too far to the open or closed side, shoulder force and torque may increase (Davis et al., 2009; Fortenbaugh et al., 2009). At the instant of foot contact, measurements of throwing arm position are valuable in assessing kinetic chain timing between the body and upper extremity. Insufficient shoulder external rotation at the time of foot contact may indicate poor timing, resulting in increased arm kinetics and decreased performance (Fleisig et al., 2015). Excessive shoulder external rotation at foot contact may also decrease ball velocity and performance (Escamilla, Fleisig, Barrentine, Andrews, & Moorman, 2002). During the arm acceleration and arm deceleration phases, the humeral head must stay centred in the glenoid fossa. Muscular imbalance about the shoulder or abduction significantly below or above 90° can lead to impingement or labral injury (Fleisig, Escamilla, & Barrentine, 1998). Deviation from 90° of abduction has also been associated with decreased ball velocity (Matsuo, Fleisig, Zheng, & Andrews, 2006; Stodden, Fleisig, McLean, & Andrews, 2005). The kinetic chain sequence allows a pitcher to transfer and build energy up the body from the lower extremities to the upper extremity, through the trunk. Specifically, the maximum angular velocity of the upper trunk should occur shortly after maximum angular velocity of the pelvis. Improper timing between foot contact, pelvis rotation, and upper trunk rotation has been associated with decreased ball velocity, increased kinetics and increased risk of shoulder injury (Douoguih, Dolce, & Lincoln, 2015; Stodden, Fleisig, McLean, Lyman, & Andrews, 2001; Urbin, Fleisig, Abebe, & Andrews, 2013). Another component of the kinetic chain is the front knee extension through ball release, decelerating the lead hip’s forward motion and enabling pelvis rotation and trunk forward flexion (Stodden et al., 2005).