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Syncope: Physiology, Pathophysiology and Aeromedical Implications
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
David A. Low, Christopher J. Mathias
Autonomic (neurally) mediated syncope is regarded as the most common cause of intermittent and usually extremely short-lived autonomic cardiovascular dysfunction. Another cause of intermittent autonomic dysfunction, mainly associated with postural change and exercise, which only recently has been recognized, is the postural tachycardia syndrome (PoTS) (Schondorf and Low, 1993). This syndrome is characterized by a substantial rise in heart rate (> 30 beats.min-1) and orthostatic intolerance symptoms attributed to cerebral hypoperfusion and sympathetic over-activation (palpitations, tremulousness and sweating) but without orthostatic hypotension (Figure 13.6b) (Mathias, 2009). In our experience, syncope also occurs in a third of such patients investigated, although symptoms in the presyncopal phase, especially palpitations, enable them to take preventive action. It predominantly affects women below the age of 50 years and may be preceded by a viral illness. Fatigue occurs in some, and prolonged physical inactivity (for example, deconditioning) and hyperventilation may be contributory. The most common associated disorder, in our experience, is the joint hypermobility syndrome (Ehlers–Danlos III).
Upper extremity injuries
Published in Youlian Hong, Roger Bartlett, Routledge Handbook of Biomechanics and Human Movement Science, 2008
Ronald F. Zernicke, William C. Whiting, Sarah L. Manske
Specific aspects of the swimming stroke can affect susceptibility to injury. For example, using a straight arm during recovery and/or insufficient body roll can lead to shoulder impingement. Body roll allows the shoulder to function in a more neutral position relative to the coronal plane, which improves efficiency and requires less force to achieve the same forward propulsion. In addition, elite swimmers have greater shoulder laxity (i.e., hypermobility) than recreational swimmers (Zemek and Magee, 1996), which can effectively increase ROM but lead to joint instability. The increased flexibility that this laxity creates at the glenohumeral joint increases the swimmer’s ability to generate power throughout the full pull-through phase (Troup, 1999). Use of hand paddles as a training tool increases the resistance provided by water, and thus increases the force production on internal rotation, which can further reduce joint stability (Weldon and Richardson, 2001).
Effects of body position and centre of gravity on tolerance of seated postures
Published in Rani Lueder, Kageyu Noro, Hard Facts about Soft Machines:, 2020
S. Reinecke, G. Weisman, M. H. Pope
Subjects reported pain in the low and middle back for much of the testing time, suggesting that posture tolerance time may be a function of the muscles. Biering-Sorensen’s (1984) prospective study on low back pain in men revealed that the two most important risk factors for first time occurrence of low back trouble were poor isometric endurance of the back muscles and hypermobility of the lumbar spine in flexion. He suggested that good back muscle endurance should, to some extent, protect one against low back trouble. He further pointed out that back muscles, since they maintain the erect posture of the spine throughout the day, must require a certain isometric endurance – a degree of endurance probably also essential to many manual handling tasks.
A comparative finite element analysis of artificial intervertebral disc replacement and pedicle screw fixation of the lumbar spine
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Jayanta Kumar Biswas, Anindya Malas, Sourav Majumdar, Masud Rana
The low coefficient of friction between UHMWPE and metal endplate of ball-socket type TDR could not produce enough resistance to stabilize the segment. It has been reported in surgical simulation that the intervertebral disc and the anterior longitudinal ligament of the segment have been fully surgically excised, and postural stability has been lost. As a result, the mobility of the segment may increase as compared to the intact spine segment. It can be said that the removal of the ligaments and insertion of the ball-socket type articulating implant increases flexibility in the implanted segment. This increment in flexibility which is also known as hypermobility may generate unusually high strains on the ligaments and muscles.