We recruited four study groups, each with five subjects. All subjects underwent normal spirometry. Subjects breathed through a snugly fit facemask, and a one-way valve separated inspiratory and expiratory airflow. Airflow, frequency, and volume were measured continuously. Each session consisted of 90 min. For the first 30 min, the subjects breathed with no inspiratory load present. In the last 60 min, the load varied according to group assignment: group 1, no inspiratory load; group 2, low inspiratory load (1.3 cm H2O/L/s); or group 3, medium inspiratory load (3.4 cm H2O/L/s); or group 4, heavy inspiratory load (14.1 cm H2O/L/s). Trials were repeated on 3 consecutive days for the first three groups and for 4 days for the fourth group. Borg scores were obtained at the beginning and the end of the first 30 min, and at the beginning of loaded breathing and every 30 min thereafter. Anxiety was measured using the State-Trait Anxiety Inventory.