[Purpose] Breathing exercises are frequently prescribed to reduce pulmonary complications after abdominal and thoracic surgery. Appropriate instructions ensuring the integrity of the self-exercise are important. This study compared the effects of two instructions, focusing on non-specific breathing (NB) and diaphragmatic breathing (DB) patterns, respectively, on the ventilatory efficiency and work of breathing. [Subjects and Methods] The participants were healthy men (n=15) and women (n=15). Ventilatory parameters, heart rate, and autonomic nervous system activity were measured during natural and deep breathing phases performed under the two instructions (NB and DB), with the deep breathing phase following the natural breathing phase. [Results] For both men and women, ventilatory efficiency was increased during deep breathing relative to natural breathing, regardless of the instructions. In women, the increment in ventilatory efficiency during deep breathing was greater under NB compared to that under DB. The work of breathing decreased during deep breathing in women under both instructions, but did not change in men under DB. [Conclusion] Under NB instruction, deep breathing elicits similar or greater effects on ventilatory efficiency compared to that under DB instruction.
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