Effect of upper body posture on forced inspiration and expiration.

The upper body posture naturally adopted by long distance runners was quantified, and its effects on ventilation were assessed in 14 subjects. Maximum voluntary ventilation (MVV) and flow-volume loop maneuvers were performed in three seated positions: 1) natural running posture (RUN), with back angled forward 11 degrees, neck flexed, and head extended 35 degrees forward of the spinal column; 2) back vertical with head and neck as above (NEF); and 3) head and back vertical (VERT). MVV was significantly higher in RUN compared with both NEF and VERT, as were peak inspiratory pressure (PImax) from functional residual capacity, peak expiratory flow (PEF), and peak inspiratory flow (PIF). Expiratory flow at 50% of vital capacity was significantly higher in RUN and NEF than in VERT, consistent with reported increases in flow due to tracheal stiffening. The increased PIF and PImax in RUN indicate increased inspiratory muscle tension and/or improved transduction of tension into a more negative pleural pressure. Magnetometer tracings of rib cage dimensions demonstrated greater anteroposterior stability during maximal inspiratory efforts in RUN compared with VERT. The improved inspiratory function seen in RUN may be due to more effective diaphragmatic and/or accessory muscle function. These findings demonstrate that the position naturally adopted by long distance runners favors ventilation.