Diaphragm recruitment during nonrespiratory activities

We previously found that weight lifters could generate greater inspiratory pressures and had more diaphragm mass than control subjects. We postulated that the weight-lifting activity itself provided a strength-training stimulus to the diaphragm. To evaluate the extent to which the diaphragm is recruited during strenuous nonrespiratory activities, we measured transdiaphragmatic pressure (Pdi) in six healthy subjects during biceps curls, bench press, power lift, and sit-ups. Each maneuver was performed with and without added weight (control), and with and without an abdominal binder. The weighted maneuvers were performed either during inspiration or expiration. Maximal static transdiaphragmatic pressure (Pdi(max)) was measured during a combined inspiratory and expulsive maneuver. Group mean values of Pdi increased during all activities when compared with control (57 +/- 24 versus 18 +/- 10 cm H(2)O [mean +/- SD] [p < 0.001]), as task intensity increased (98 +/- 14 versus 35 +/- 13 cm H(2)O for high- and low-intensity activities, respectively) (p < 0.001), and with abdominal binding (75 +/- 25 versus 59 +/- 25 cm H(2)O) (p < 0.05). Peak levels of Pdi attained during the activities were 126 +/- 11 cm H(2)O or 0.65 +/- 0.09 of Pdi(max). Changes in gastric pressure accounted for 85 +/- 4% of the increase in Pdi during the activities whereas it accounted for only 58 +/- 9% of the rise in Pdi during the control activities (p < 0.001). We conclude that during a range of weight-lifting activities, the diaphragm is recruited and Pdi is raised to a level that may provide a significant strength-training stimulus to the diaphragm.