Applied anatomy and kinesiology; the mechanism of muscular movement . muscles, as we have seen, to hold up the upper chest andkeep it expanded. The drooping of head and neck that we have inkyphosis deprives these muscles of their solid points of origin andallows the sternum and ribs to sink. The exaggeration of thethoracic curve also depresses the upper ribs. All this flattens theupper chest, lessens the range of the normal movements of quietbreathing and leaves some parts of the lungs unused. The heart,stomach, liver and other organs are crowded and their functions 256 THE UPRIGHT POSITION hi
Applied anatomy and kinesiology; the mechanism of muscular movement . muscles, as we have seen, to hold up the upper chest andkeep it expanded. The drooping of head and neck that we have inkyphosis deprives these muscles of their solid points of origin andallows the sternum and ribs to sink. The exaggeration of thethoracic curve also depresses the upper ribs. All this flattens theupper chest, lessens the range of the normal movements of quietbreathing and leaves some parts of the lungs unused. The heart,stomach, liver and other organs are crowded and their functions 256 THE UPRIGHT POSITION hindered. General vitality is lowered and the tendency to lungdiseases markedly increased. The cause of kyphosis is a failure of the extensor muscles of theupper spine to hold the head and neck up in erect position. Theposture may become habitual through muscular or nervous weak-ness or as the result of occupation. Many occupations give riseto the fault but of all occupations reading probably is responsiblefor most cases. Since reading is rapidly becoming a universal. Fig. —Bad posture due to reading with the book held too low.(Photo by American Posture League.) habit among civihzed people, its causing kjphosis is a seriousmenace to racial vigor. How and why does it have this bad effecton posture ? VMien one sits erect and reads from a page at the height of theeyes he is not very likely to acquire round shoulders, although thefixed position of the head leads in time to fatigue of the neckmuscles and this in turn to a drooping posture; but if the head isheld in good position the tendency to fatigue is not marked unless DEFECTS OF POSTURE 257 the muscles are especially weak. The drooped position is broughtabout quickly because the effort to hold the arras and book up towhere the book ought to be very soon becomes uncomfortable andwe let the book drop, and then we have to take a position of roundshoulders to see the page (Fig. 153). What is quite as important,chairs do not fi
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