training device 12 and a target generator 14 connecting the resistive training device 12 to the target generator 14 is a pressure transfer tube 16 the resistive training device 12 includes a mouthpiece 18 a pressure monitoring port 20 an air restriction orifice 22 and a one way valve 24 during breathing exercises the trainee holds the resistive training device 12 by the mouthpiece 18 in his mouth and breathes only through the resistive training device 12 when inhaling air is brought into the resistive training device 12 through the orifice 22 because the one way valve 24 closes on exhaling air is passed through both the orifice 22 and the one way valve 24 which is then opened it has been found that varying the size of the orifice 22 may not aid in developing inspiratory muscle endurance instead by using the method of the present invention and an orifice 22 with a constant cross sectional area of 0 17 square centimeters for passage of air useful levels of inspiratory muscle work can be achieved further this cross sectional area for the orifice 22 allows trainees to breath through the resistive training device 12 without significantly changing the percentage of carbon dioxide in the blood stream irrespective of the level of inspiratory muscle work used to.