Inspiratory muscle function following abdominal weight exercises in healthy subjects

Three indexes of inspiratory muscle function were evaluated in 20 healthy young adults before and after a six-week program of diaphragmatic breathing exercises. Thrice weekly, each subject performed 30 maximal voluntary diaphragmatic contractions in the supine position with a moderately heavy weight (range: 7-23 kg, or 15.4-50.7 lb) placed on the anterior abdominal wall to resist diaphragmatic descent. This protocol failed to improve 1) inspiratory capacity, 2) peak inspiratory flow rate, and 3) maximal pressures generated by the inspiratory muscles under static conditions. These finding indicated that this commonly used isotonic exercise regimen does not increase the maximal shortening, velocity of shortening, or strength of the diaphragm in healthy subjects. On the other hand, most subjects increased the maximal weight they found tolerable, performed the exercise more rapidly, and reported that their initial discomfort either waned or disappeared by the end of the program. These latter observations suggest that the exercise program might have improved inspiratory muscle endurance.