Much dispute exists regarding breathing patterns during exercise. It is held by some that inhaling on the descent and exhaling on the ascent is a respectable way to lower the peak blood pressure during the repetition and thus reduce the possibility of cerebrovascular accidents occurring during exercise. Such counsel exposes a misunderstanding of the mechanisms involved, overestimates the prospect of an exercise-related cerebrovascular injury (an astoundingly scarce event), and undervalues the probability of an orthopaedic injury, a much more common event. The Valsalva manoeuvre is the accurate term for holding the breath against a shut glottis while pressure is applied by the abdominal and thoracic musculature. When you inhale, your diaphragm contracts and the size of your thoracic cavity increases. As air moves into your now bigger lungs, pressure balances between the outside and the inside. When you make an effort to hold your breath and tense your trunk muscles, you generate a pressure gradient between the inside and the outside. This pressure increases noticeably with the intensity of the squeeze. Since your thoracic and abdominal cavities are alienated by solely your diaphragm, abdominal pressure increases as well. The spinal vertebrae are being maintained in the proper anatomical position by your back muscles. This proper position is strengthened by static pressure diffused to the spine across the fundamentally non-compressible innards of the abdominal cavity. The collective efforts of increased lung (intra-thoracic) compression, intra-abdominal pressure fashioned by abdominal muscle contraction, and spinal erector contraction increases spinal stability during loading. The Valsalva manoeuvre increases the capacity to yield this pressure and stability. Exhalation during heavy labours thwarts the development of adequate pressure to stabilise the spine and therefore invites a painful injury that may linger for quite some time.
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